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-rw-r--r--src/libstore/Makefile.am11
-rw-r--r--src/libstore/build.cc498
-rw-r--r--src/libstore/derivations.hh4
-rw-r--r--src/libstore/gc.cc88
-rw-r--r--src/libstore/globals.cc2
-rw-r--r--src/libstore/local-store.cc1063
-rw-r--r--src/libstore/local-store.hh104
-rw-r--r--src/libstore/misc.cc8
-rw-r--r--src/libstore/remote-store.cc42
-rw-r--r--src/libstore/remote-store.hh6
-rw-r--r--src/libstore/schema.sql43
-rw-r--r--src/libstore/store-api.cc13
-rw-r--r--src/libstore/store-api.hh35
-rw-r--r--src/libstore/worker-protocol.hh4
14 files changed, 1127 insertions, 794 deletions
diff --git a/src/libstore/Makefile.am b/src/libstore/Makefile.am
index 9accc3005fc3..e19256b925ea 100644
--- a/src/libstore/Makefile.am
+++ b/src/libstore/Makefile.am
@@ -10,7 +10,14 @@ pkginclude_HEADERS = \
   globals.hh references.hh pathlocks.hh \
   worker-protocol.hh
 
-libstore_la_LIBADD = ../libutil/libutil.la ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
+libstore_la_LIBADD = ../libutil/libutil.la ../boost/format/libformat.la ${aterm_lib} ${sqlite_lib}
+
+EXTRA_DIST = schema.sql
 
 AM_CXXFLAGS = -Wall \
- -I$(srcdir)/.. -I$(srcdir)/../libutil
+ ${sqlite_include} -I$(srcdir)/.. -I$(srcdir)/../libutil
+
+local-store.lo: schema.sql.hh
+
+%.sql.hh: %.sql
+	../bin2c/bin2c schema < $< > $@ || (rm $@ && exit 1)
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index ef2f7adf3194..210486fbc205 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -64,6 +64,7 @@ static const uid_t rootUserId = 0;
 
 /* Forward definition. */
 class Worker;
+class HookInstance;
 
 
 /* A pointer to a goal. */
@@ -215,6 +216,8 @@ public:
 
     LocalStore & store;
 
+    boost::shared_ptr<HookInstance> hook;
+    
     Worker(LocalStore & store);
     ~Worker();
 
@@ -615,6 +618,107 @@ void deletePathWrapped(const Path & path)
 //////////////////////////////////////////////////////////////////////
 
 
+struct HookInstance
+{
+    /* Pipes for talking to the build hook. */
+    Pipe toHook;
+
+    /* Pipe for the hook's standard output/error. */
+    Pipe fromHook;
+
+    /* Pipe for the builder's standard output/error. */
+    Pipe builderOut;
+    
+    /* The process ID of the hook. */
+    Pid pid;
+
+    HookInstance();
+
+    ~HookInstance();
+};
+
+
+HookInstance::HookInstance()
+{
+    debug("starting build hook");
+    
+    Path buildHook = absPath(getEnv("NIX_BUILD_HOOK"));
+    
+    /* Create a pipe to get the output of the child. */
+    fromHook.create();
+    
+    /* Create the communication pipes. */
+    toHook.create();
+
+    /* Create a pipe to get the output of the builder. */
+    builderOut.create();
+
+    /* Fork the hook. */
+    pid = fork();
+    switch (pid) {
+        
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0:
+        try { /* child */
+
+            commonChildInit(fromHook);
+
+            if (chdir("/") == -1) throw SysError("changing into `/");
+            
+            /* Dup the communication pipes. */
+            toHook.writeSide.close();
+            if (dup2(toHook.readSide, STDIN_FILENO) == -1)
+                throw SysError("dupping to-hook read side");
+
+            /* Use fd 4 for the builder's stdout/stderr. */
+            builderOut.readSide.close();
+            if (dup2(builderOut.writeSide, 4) == -1)
+                throw SysError("dupping builder's stdout/stderr");
+            
+            execl(buildHook.c_str(), buildHook.c_str(), thisSystem.c_str(),
+                (format("%1%") % maxSilentTime).str().c_str(),
+                (format("%1%") % printBuildTrace).str().c_str(),
+                NULL);
+            
+            throw SysError(format("executing `%1%'") % buildHook);
+            
+        } catch (std::exception & e) {
+            std::cerr << format("build hook error: %1%") % e.what() << std::endl;
+        }
+        quickExit(1);
+    }
+    
+    /* parent */
+    pid.setSeparatePG(true);
+    pid.setKillSignal(SIGTERM);
+    fromHook.writeSide.close();
+    toHook.readSide.close();
+}
+
+
+HookInstance::~HookInstance()
+{
+    try {
+        /* Cleanly shut down the hook by closing its stdin if it's not
+           already building.  Otherwise pid's destructor will kill
+           it. */
+        if (pid != -1 && toHook.writeSide != -1) {
+            toHook.writeSide.close();
+            pid.wait(true);
+        }
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+typedef enum {rpAccept, rpDecline, rpPostpone} HookReply;
+
 class DerivationGoal : public Goal
 {
 private:
@@ -649,14 +753,11 @@ private:
     AutoCloseFD fdLogFile;
 
     /* Pipe for the builder's standard output/error. */
-    Pipe logPipe;
-
-    /* Whether we're building using a build hook. */
-    bool usingBuildHook;
-
-    /* Pipes for talking to the build hook (if any). */
-    Pipe toHook;
+    Pipe builderOut;
 
+    /* The build hook. */
+    boost::shared_ptr<HookInstance> hook;
+    
     /* Whether we're currently doing a chroot build. */
     bool useChroot;
     
@@ -694,12 +795,8 @@ private:
     void buildDone();
 
     /* Is the build hook willing to perform the build? */
-    typedef enum {rpAccept, rpDecline, rpPostpone} HookReply;
     HookReply tryBuildHook();
 
-    /* Synchronously wait for a build hook to finish. */
-    void terminateBuildHook(bool kill = false);
-
     /* Start building a derivation. */
     void startBuilder();
 
@@ -711,10 +808,6 @@ private:
     /* Open a log file and a pipe to it. */
     Path openLogFile();
 
-    /* Common initialisation to be performed in child processes (i.e.,
-       both in builders and in build hooks). */
-    void initChild();
-    
     /* Delete the temporary directory, if we have one. */
     void deleteTmpDir(bool force);
 
@@ -742,6 +835,7 @@ DerivationGoal::DerivationGoal(const Path & drvPath, Worker & worker)
     trace("created");
 }
 
+
 DerivationGoal::~DerivationGoal()
 {
     /* Careful: we should never ever throw an exception from a
@@ -754,6 +848,7 @@ DerivationGoal::~DerivationGoal()
     }
 }
 
+
 void DerivationGoal::killChild()
 {
     if (pid != -1) {
@@ -778,6 +873,8 @@ void DerivationGoal::killChild()
         
         assert(pid == -1);
     }
+
+    hook.reset();
 }
 
 
@@ -887,7 +984,10 @@ void DerivationGoal::outputsSubstituted()
     foreach (PathSet::iterator, i, drv.inputSrcs)
         addWaitee(worker.makeSubstitutionGoal(*i));
 
-    state = &DerivationGoal::inputsRealised;
+    if (waitees.empty()) /* to prevent hang (no wake-up event) */
+        inputsRealised();
+    else
+        state = &DerivationGoal::inputsRealised;
 }
 
 
@@ -961,6 +1061,16 @@ PathSet outputPaths(const DerivationOutputs & outputs)
 }
 
 
+static bool canBuildLocally(const string & platform)
+{
+    return platform == thisSystem 
+#ifdef CAN_DO_LINUX32_BUILDS
+        || (platform == "i686-linux" && thisSystem == "x86_64-linux")
+#endif
+        ;
+}
+
+
 void DerivationGoal::tryToBuild()
 {
     trace("trying to build");
@@ -1028,28 +1138,36 @@ void DerivationGoal::tryToBuild()
     foreach (DerivationOutputs::iterator, i, drv.outputs)
         if (pathFailed(i->second.path)) return;
 
+    /* Don't do a remote build if the derivation has the attribute
+       `preferLocalBuild' set. */
+    bool preferLocalBuild =
+        drv.env["preferLocalBuild"] == "1" && canBuildLocally(drv.platform);
+
     /* Is the build hook willing to accept this job? */
-    usingBuildHook = true;
-    switch (tryBuildHook()) {
-        case rpAccept:
-            /* Yes, it has started doing so.  Wait until we get EOF
-               from the hook. */
-            state = &DerivationGoal::buildDone;
-            return;
-        case rpPostpone:
-            /* Not now; wait until at least one child finishes. */
-            worker.waitForAWhile(shared_from_this());
-            outputLocks.unlock();
-            return;
-        case rpDecline:
-            /* We should do it ourselves. */
-            break;
+    if (!preferLocalBuild) {
+        switch (tryBuildHook()) {
+            case rpAccept:
+                /* Yes, it has started doing so.  Wait until we get
+                   EOF from the hook. */
+                state = &DerivationGoal::buildDone;
+                return;
+            case rpPostpone:
+                /* Not now; wait until at least one child finishes or
+                   the wake-up timeout expires. */
+                worker.waitForAWhile(shared_from_this());
+                outputLocks.unlock();
+                return;
+            case rpDecline:
+                /* We should do it ourselves. */
+                break;
+        }
     }
-
-    usingBuildHook = false;
-
-    /* Make sure that we are allowed to start a build. */
-    if (worker.getNrLocalBuilds() >= maxBuildJobs) {
+    
+    /* Make sure that we are allowed to start a build.  If this
+       derivation prefers to be done locally, do it even if
+       maxBuildJobs is 0. */
+    unsigned int curBuilds = worker.getNrLocalBuilds();
+    if (curBuilds >= maxBuildJobs && !(preferLocalBuild && curBuilds == 0)) {
         worker.waitForBuildSlot(shared_from_this());
         outputLocks.unlock();
         return;
@@ -1085,18 +1203,29 @@ void DerivationGoal::buildDone()
        to have terminated.  In fact, the builder could also have
        simply have closed its end of the pipe --- just don't do that
        :-) */
-    /* !!! this could block! security problem! solution: kill the
-       child */
-    pid_t savedPid = pid;
-    int status = pid.wait(true);
+    int status;
+    pid_t savedPid;
+    if (hook) {
+        savedPid = hook->pid;
+        status = hook->pid.wait(true);
+    } else {
+        /* !!! this could block! security problem! solution: kill the
+           child */
+        savedPid = pid;
+        status = pid.wait(true);
+    }
 
     debug(format("builder process for `%1%' finished") % drvPath);
 
     /* So the child is gone now. */
     worker.childTerminated(savedPid);
-
+    
     /* Close the read side of the logger pipe. */
-    logPipe.readSide.close();
+    if (hook) {
+        hook->builderOut.readSide.close();
+        hook->fromHook.readSide.close();
+    }
+    else builderOut.readSide.close();
 
     /* Close the log file. */
     fdLogFile.close();
@@ -1169,11 +1298,11 @@ void DerivationGoal::buildDone()
         /* When using a build hook, the hook will return a remote
            build failure using exit code 100.  Anything else is a hook
            problem. */
-        bool hookError = usingBuildHook &&
+        bool hookError = hook &&
             (!WIFEXITED(status) || WEXITSTATUS(status) != 100);
         
         if (printBuildTrace) {
-            if (usingBuildHook && hookError)
+            if (hook && hookError)
                 printMsg(lvlError, format("@ hook-failed %1% %2% %3% %4%")
                     % drvPath % drv.outputs["out"].path % status % e.msg());
             else
@@ -1208,162 +1337,85 @@ void DerivationGoal::buildDone()
 }
 
 
-DerivationGoal::HookReply DerivationGoal::tryBuildHook()
+HookReply DerivationGoal::tryBuildHook()
 {
-    if (!useBuildHook) return rpDecline;
-    Path buildHook = getEnv("NIX_BUILD_HOOK");
-    if (buildHook == "") return rpDecline;
-    buildHook = absPath(buildHook);
-
-    /* Create a directory where we will store files used for
-       communication between us and the build hook. */
-    tmpDir = createTempDir();
-    
-    /* Create the log file and pipe. */
-    Path logFile = openLogFile();
-
-    /* Create the communication pipes. */
-    toHook.create();
-
-    /* Fork the hook. */
-    pid = fork();
-    switch (pid) {
-        
-    case -1:
-        throw SysError("unable to fork");
-
-    case 0:
-        try { /* child */
-
-            initChild();
+    if (!useBuildHook || getEnv("NIX_BUILD_HOOK") == "") return rpDecline;
 
-            string s;
-            foreach (DerivationOutputs::const_iterator, i, drv.outputs)
-                s += i->second.path + " ";
-            if (setenv("NIX_HELD_LOCKS", s.c_str(), 1))
-                throw SysError("setting an environment variable");
+    if (!worker.hook)
+        worker.hook = boost::shared_ptr<HookInstance>(new HookInstance);
 
-            execl(buildHook.c_str(), buildHook.c_str(),
-                (worker.getNrLocalBuilds() < maxBuildJobs ? (string) "1" : "0").c_str(),
-                thisSystem.c_str(),
-                drv.platform.c_str(),
-                drvPath.c_str(),
-                (format("%1%") % maxSilentTime).str().c_str(),
-                NULL);
-            
-            throw SysError(format("executing `%1%'") % buildHook);
-            
-        } catch (std::exception & e) {
-            std::cerr << format("build hook error: %1%") % e.what() << std::endl;
-        }
-        quickExit(1);
-    }
-    
-    /* parent */
-    pid.setSeparatePG(true);
-    pid.setKillSignal(SIGTERM);
-    logPipe.writeSide.close();
-    worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), false, false);
+    /* Tell the hook about system features (beyond the system type)
+       required from the build machine.  (The hook could parse the
+       drv file itself, but this is easier.) */
+    Strings features = tokenizeString(drv.env["requiredSystemFeatures"]);
+    foreach (Strings::iterator, i, features) checkStoreName(*i); /* !!! abuse */
 
-    toHook.readSide.close();
+    /* Send the request to the hook. */
+    writeLine(worker.hook->toHook.writeSide, (format("%1% %2% %3% %4%")
+        % (worker.getNrLocalBuilds() < maxBuildJobs ? "1" : "0")
+        % drv.platform % drvPath % concatStringsSep(",", features)).str());
 
     /* Read the first line of input, which should be a word indicating
        whether the hook wishes to perform the build. */
     string reply;
-    try {
-        while (true) {
-            string s = readLine(logPipe.readSide);
-            if (string(s, 0, 2) == "# ") {
-                reply = string(s, 2);
-                break;
-            }
-            handleChildOutput(logPipe.readSide, s + "\n");
+    while (true) {
+        string s = readLine(worker.hook->fromHook.readSide);
+        if (string(s, 0, 2) == "# ") {
+            reply = string(s, 2);
+            break;
         }
-    } catch (Error & e) {
-        terminateBuildHook(true);
-        throw;
+        s += "\n";
+        writeToStderr((unsigned char *) s.c_str(), s.size());
     }
 
     debug(format("hook reply is `%1%'") % reply);
 
-    if (reply == "decline" || reply == "postpone") {
-        /* Clean up the child.  !!! hacky / should verify */
-        terminateBuildHook();
+    if (reply == "decline" || reply == "postpone")
         return reply == "decline" ? rpDecline : rpPostpone;
-    }
+    else if (reply != "accept")
+        throw Error(format("bad hook reply `%1%'") % reply);
 
-    else if (reply == "accept") {
+    printMsg(lvlTalkative, format("using hook to build path(s) %1%")
+        % showPaths(outputPaths(drv.outputs)));
 
-        printMsg(lvlInfo, format("using hook to build path(s) %1%")
-            % showPaths(outputPaths(drv.outputs)));
-        
-        /* Write the information that the hook needs to perform the
-           build, i.e., the set of input paths, the set of output
-           paths, and the references (pointer graph) in the input
-           paths. */
+    hook = worker.hook;
+    worker.hook.reset();
         
-        Path inputListFN = tmpDir + "/inputs";
-        Path outputListFN = tmpDir + "/outputs";
-        Path referencesFN = tmpDir + "/references";
-
-        /* The `inputs' file lists all inputs that have to be copied
-           to the remote system.  This unfortunately has to contain
-           the entire derivation closure to ensure that the validity
-           invariant holds on the remote system.  (I.e., it's
-           unfortunate that we have to list it since the remote system
-           *probably* already has it.) */
-        PathSet allInputs;
-        allInputs.insert(inputPaths.begin(), inputPaths.end());
-        computeFSClosure(drvPath, allInputs);
+    /* Tell the hook all the inputs that have to be copied to the
+       remote system.  This unfortunately has to contain the entire
+       derivation closure to ensure that the validity invariant holds
+       on the remote system.  (I.e., it's unfortunate that we have to
+       list it since the remote system *probably* already has it.) */
+    PathSet allInputs;
+    allInputs.insert(inputPaths.begin(), inputPaths.end());
+    computeFSClosure(drvPath, allInputs);
         
-        string s;
-        foreach (PathSet::iterator, i, allInputs) s += *i + "\n";
+    string s;
+    foreach (PathSet::iterator, i, allInputs) s += *i + " ";
+    writeLine(hook->toHook.writeSide, s);
         
-        writeFile(inputListFN, s);
-
-        /* The `outputs' file lists all outputs that have to be copied
-           from the remote system. */
-        s = "";
-        foreach (DerivationOutputs::iterator, i, drv.outputs)
-            s += i->second.path + "\n";
-        writeFile(outputListFN, s);
-
-        /* The `references' file has exactly the format accepted by
-           `nix-store --register-validity'. */
-        writeFile(referencesFN,
-            makeValidityRegistration(allInputs, true, false));
+    /* Tell the hooks the outputs that have to be copied back from the
+       remote system. */
+    s = "";
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        s += i->second.path + " ";
+    writeLine(hook->toHook.writeSide, s);
+    
+    hook->toHook.writeSide.close();
 
-        /* Tell the hook to proceed. */
-        writeLine(toHook.writeSide, "okay");
-        toHook.writeSide.close();
+    /* Create the log file and pipe. */
+    Path logFile = openLogFile();
 
-        if (printBuildTrace)
-            printMsg(lvlError, format("@ build-started %1% %2% %3% %4%")
-                % drvPath % drv.outputs["out"].path % drv.platform % logFile);
+    set<int> fds;
+    fds.insert(hook->fromHook.readSide);
+    fds.insert(hook->builderOut.readSide);
+    worker.childStarted(shared_from_this(), hook->pid, fds, false, false);
+    
+    if (printBuildTrace)
+        printMsg(lvlError, format("@ build-started %1% %2% %3% %4%")
+            % drvPath % drv.outputs["out"].path % drv.platform % logFile);
         
-        return rpAccept;
-    }
-
-    else throw Error(format("bad hook reply `%1%'") % reply);
-}
-
-
-void DerivationGoal::terminateBuildHook(bool kill)
-{
-    debug("terminating build hook");
-    pid_t savedPid = pid;
-    if (kill)
-        pid.kill();
-    else
-        pid.wait(true);
-    /* `false' means don't wake up waiting goals, since we want to
-       keep this build slot ourselves. */
-    worker.childTerminated(savedPid, false);
-    toHook.writeSide.close();
-    fdLogFile.close();
-    logPipe.readSide.close();
-    deleteTmpDir(true); /* get rid of the hook's temporary directory */
+    return rpAccept;    
 }
 
 
@@ -1380,11 +1432,7 @@ void DerivationGoal::startBuilder()
         format("building path(s) %1%") % showPaths(outputPaths(drv.outputs)))
     
     /* Right platform? */
-    if (drv.platform != thisSystem 
-#ifdef CAN_DO_LINUX32_BUILDS
-        && !(drv.platform == "i686-linux" && thisSystem == "x86_64-linux")
-#endif
-        )
+    if (!canBuildLocally(drv.platform))
         throw Error(
             format("a `%1%' is required to build `%3%', but I am a `%2%'")
             % drv.platform % thisSystem % drvPath);
@@ -1549,6 +1597,9 @@ void DerivationGoal::startBuilder()
 
     if (fixedOutput) useChroot = false;
 
+    /* Hack to allow derivations to disable chroot builds. */
+    if (drv.env["__noChroot"] == "1") useChroot = false;
+
     if (useChroot) {
 #if CHROOT_ENABLED
         /* Create a temporary directory in which we set up the chroot
@@ -1572,7 +1623,7 @@ void DerivationGoal::startBuilder()
 
         /* Create a /etc/passwd with entries for the build user and the
            nobody account.  The latter is kind of a hack to support
-           Samba-in-QEMU.  */
+           Samba-in-QEMU. */
         createDirs(chrootRootDir + "/etc");
 
         writeFile(chrootRootDir + "/etc/passwd",
@@ -1580,13 +1631,13 @@ void DerivationGoal::startBuilder()
                 "nixbld:x:%1%:%2%:Nix build user:/:/noshell\n"
                 "nobody:x:65534:65534:Nobody:/:/noshell\n")
                 % (buildUser.enabled() ? buildUser.getUID() : getuid())
-	        % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
+                % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
 
 	/* Declare the build user's group so that programs get a consistent
-	   view of the system (e.g., "id -gn").  */
-	writeFile(chrootRootDir + "/etc/group",
-		  (format("nixbld:!:%1%:\n")
-		   % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
+	   view of the system (e.g., "id -gn"). */
+        writeFile(chrootRootDir + "/etc/group",
+            (format("nixbld:!:%1%:\n")
+                % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
 
         /* Bind-mount a user-configurable set of directories from the
            host file system.  The `/dev/pts' directory must be mounted
@@ -1645,9 +1696,12 @@ void DerivationGoal::startBuilder()
     printMsg(lvlChatty, format("executing builder `%1%'") %
         drv.builder);
 
-    /* Create the log file and pipe. */
+    /* Create the log file. */
     Path logFile = openLogFile();
     
+    /* Create a pipe to get the output of the builder. */
+    builderOut.create();
+
     /* Fork a child to build the package.  Note that while we
        currently use forks to run and wait for the children, it
        shouldn't be hard to use threads for this on systems where
@@ -1688,18 +1742,23 @@ void DerivationGoal::startBuilder()
                         throw SysError(format("bind mount from `%1%' to `%2%' failed") % source % target);
                 }
                     
-                /* Do the chroot().  initChild() will do a chdir() to
-                   the temporary build directory to make sure the
-                   current directory is in the chroot.  (Actually the
-                   order doesn't matter, since due to the bind mount
-                   tmpDir and tmpRootDit/tmpDir are the same
-                   directories.) */
+                /* Do the chroot().  Below we do a chdir() to the
+                   temporary build directory to make sure the current
+                   directory is in the chroot.  (Actually the order
+                   doesn't matter, since due to the bind mount tmpDir
+                   and tmpRootDit/tmpDir are the same directories.) */
                 if (chroot(chrootRootDir.c_str()) == -1)
                     throw SysError(format("cannot change root directory to `%1%'") % chrootRootDir);
             }
 #endif
             
-            initChild();
+            commonChildInit(builderOut);
+    
+            if (chdir(tmpDir.c_str()) == -1)
+                throw SysError(format("changing into `%1%'") % tmpDir);
+
+            /* Close all other file descriptors. */
+            closeMostFDs(set<int>());
 
 #ifdef CAN_DO_LINUX32_BUILDS
             if (drv.platform == "i686-linux" && thisSystem == "x86_64-linux") {
@@ -1720,10 +1779,10 @@ void DerivationGoal::startBuilder()
             
             /* If we are running in `build-users' mode, then switch to
                the user we allocated above.  Make sure that we drop
-               all root privileges.  Note that initChild() above has
-               closed all file descriptors except std*, so that's
-               safe.  Also note that setuid() when run as root sets
-               the real, effective and saved UIDs. */
+               all root privileges.  Note that above we have closed
+               all file descriptors except std*, so that's safe.  Also
+               note that setuid() when run as root sets the real,
+               effective and saved UIDs. */
             if (buildUser.enabled()) {
                 printMsg(lvlChatty, format("switching to user `%1%'") % buildUser.getUser());
 
@@ -1777,9 +1836,9 @@ void DerivationGoal::startBuilder()
     
     /* parent */
     pid.setSeparatePG(true);
-    logPipe.writeSide.close();
+    builderOut.writeSide.close();
     worker.childStarted(shared_from_this(), pid,
-        singleton<set<int> >(logPipe.readSide), true, true);
+        singleton<set<int> >(builderOut.readSide), true, true);
 
     if (printBuildTrace) {
         printMsg(lvlError, format("@ build-started %1% %2% %3% %4%")
@@ -1816,7 +1875,7 @@ void DerivationGoal::computeClosure()
     /* When using a build hook, the build hook can register the output
        as valid (by doing `nix-store --import').  If so we don't have
        to do anything here. */
-    if (usingBuildHook) {
+    if (hook) {
         bool allValid = true;
         foreach (DerivationOutputs::iterator, i, drv.outputs)
             if (!worker.store.isValidPath(i->second.path)) allValid = false;
@@ -1944,32 +2003,10 @@ Path DerivationGoal::openLogFile()
     if (fdLogFile == -1)
         throw SysError(format("creating log file `%1%'") % logFileName);
 
-    /* Create a pipe to get the output of the child. */
-    logPipe.create();
-
     return logFileName;
 }
 
 
-void DerivationGoal::initChild()
-{
-    commonChildInit(logPipe);
-    
-    if (chdir(tmpDir.c_str()) == -1)
-        throw SysError(format("changing into `%1%'") % tmpDir);
-
-    /* When running a hook, dup the communication pipes. */
-    if (usingBuildHook) {
-        toHook.writeSide.close();
-        if (dup2(toHook.readSide, STDIN_FILENO) == -1)
-            throw SysError("dupping to-hook read side");
-    }
-
-    /* Close all other file descriptors. */
-    closeMostFDs(set<int>());
-}
-
-
 void DerivationGoal::deleteTmpDir(bool force)
 {
     if (tmpDir != "") {
@@ -1989,19 +2026,22 @@ void DerivationGoal::deleteTmpDir(bool force)
 
 void DerivationGoal::handleChildOutput(int fd, const string & data)
 {
-    if (fd == logPipe.readSide) {
+    if ((hook && fd == hook->builderOut.readSide) ||
+        (!hook && fd == builderOut.readSide))
+    {
         if (verbosity >= buildVerbosity)
             writeToStderr((unsigned char *) data.c_str(), data.size());
         writeFull(fdLogFile, (unsigned char *) data.c_str(), data.size());
     }
 
-    else abort();
+    if (hook && fd == hook->fromHook.readSide)
+        writeToStderr((unsigned char *) data.c_str(), data.size());
 }
 
 
 void DerivationGoal::handleEOF(int fd)
 {
-    if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
+    worker.wakeUp(shared_from_this());
 }
 
 
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 95e49d42c9ea..c14be48afb8e 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -1,10 +1,10 @@
 #ifndef __DERIVATIONS_H
 #define __DERIVATIONS_H
 
-#include "hash.hh"
-
 #include <map>
 
+#include "types.hh"
+
 
 namespace nix {
 
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index f58f691c99dd..b8395bfc4352 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -1,6 +1,5 @@
 #include "globals.hh"
 #include "misc.hh"
-#include "pathlocks.hh"
 #include "local-store.hh"
 
 #include <boost/shared_ptr.hpp>
@@ -31,7 +30,7 @@ static const int defaultGcLevel = 1000;
    read.  To be precise: when they try to create a new temporary root
    file, they will block until the garbage collector has finished /
    yielded the GC lock. */
-static int openGCLock(LockType lockType)
+int LocalStore::openGCLock(LockType lockType)
 {
     Path fnGCLock = (format("%1%/%2%")
         % nixStateDir % gcLockName).str();
@@ -127,7 +126,7 @@ Path addPermRoot(const Path & _storePath, const Path & _gcRoot,
        Instead of reading all the roots, it would be more efficient to
        check if the root is in a directory in or linked from the
        gcroots directory. */
-    if (queryBoolSetting("gc-check-reachability", true)) {
+    if (queryBoolSetting("gc-check-reachability", false)) {
         Roots roots = store->findRoots();
         if (roots.find(gcRoot) == roots.end())
             printMsg(lvlError, 
@@ -136,7 +135,7 @@ Path addPermRoot(const Path & _storePath, const Path & _gcRoot,
                     "therefore, `%2%' might be removed by the garbage collector")
                 % gcRoot % storePath);
     }
-        
+
     /* Grab the global GC root, causing us to block while a GC is in
        progress.  This prevents the set of permanent roots from
        increasing while a GC is in progress. */
@@ -416,18 +415,13 @@ struct LocalStore::GCState
     PathSet busy;
     bool gcKeepOutputs;
     bool gcKeepDerivations;
-
-    bool drvsIndexed;
-    typedef std::multimap<string, Path> DrvsByName;
-    DrvsByName drvsByName; // derivation paths hashed by name attribute
-
-    GCState(GCResults & results_) : results(results_), drvsIndexed(false)
+    GCState(GCResults & results_) : results(results_)
     {
     }
 };
 
 
-static bool doDelete(GCOptions::GCAction action)
+static bool shouldDelete(GCOptions::GCAction action)
 {
     return action == GCOptions::gcDeleteDead
         || action == GCOptions::gcDeleteSpecific;
@@ -441,45 +435,11 @@ bool LocalStore::isActiveTempFile(const GCState & state,
         && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
 }
 
-
-/* Return all the derivations in the Nix store that have `path' as an
-   output.  This function assumes that derivations have the same name
-   as their outputs. */
-PathSet LocalStore::findDerivers(GCState & state, const Path & path)
-{
-    PathSet derivers;
-
-    Path deriver = queryDeriver(path);
-    if (deriver != "") derivers.insert(deriver);
-
-    if (!state.drvsIndexed) {
-        Paths entries = readDirectory(nixStore);
-        foreach (Paths::iterator, i, entries)
-            if (isDerivation(*i))
-                state.drvsByName.insert(std::pair<string, Path>(
-                        getNameOfStorePath(*i), nixStore + "/" + *i));
-        state.drvsIndexed = true;
-    }
-    
-    string name = getNameOfStorePath(path);
-
-    // Urgh, I should have used Haskell...
-    std::pair<GCState::DrvsByName::iterator, GCState::DrvsByName::iterator> range =
-        state.drvsByName.equal_range(name);
-
-    for (GCState::DrvsByName::iterator i = range.first; i != range.second; ++i)
-        if (isValidPath(i->second)) {
-            Derivation drv = derivationFromPath(i->second);
-            foreach (DerivationOutputs::iterator, j, drv.outputs)
-                if (j->second.path == path) derivers.insert(i->second);
-        }
-
-    return derivers;
-}
-
     
 bool LocalStore::tryToDelete(GCState & state, const Path & path)
 {
+    checkInterrupt();
+    
     if (!pathExists(path)) return true;
     if (state.deleted.find(path) != state.deleted.end()) return true;
     if (state.live.find(path) != state.live.end()) return false;
@@ -508,10 +468,10 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
            then don't delete the derivation if any of the outputs are
            live. */
         if (state.gcKeepDerivations && isDerivation(path)) {
-            Derivation drv = derivationFromPath(path);
-            foreach (DerivationOutputs::iterator, i, drv.outputs)
-                if (!tryToDelete(state, i->second.path)) {
-                    printMsg(lvlDebug, format("cannot delete derivation `%1%' because its output is alive") % path);
+            PathSet outputs = queryDerivationOutputs(path);
+            foreach (PathSet::iterator, i, outputs)
+                if (!tryToDelete(state, *i)) {
+                    printMsg(lvlDebug, format("cannot delete derivation `%1%' because its output `%2%' is alive") % path % *i);
                     goto isLive;
                 }
         }
@@ -522,18 +482,9 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
         if (!pathExists(path)) return true;
 
         /* If gc-keep-outputs is set, then don't delete this path if
-           its deriver is not garbage.  !!! Nix does not reliably
-           store derivers, so we have to look at all derivations to
-           determine which of them derive `path'.  Since this makes
-           the garbage collector very slow to start on large Nix
-           stores, here we just look for all derivations that have the
-           same name as `path' (where the name is the part of the
-           filename after the hash, i.e. the `name' attribute of the
-           derivation).  This is somewhat hacky: currently, the
-           deriver of a path always has the same name as the output,
-           but this might change in the future. */
+           there are derivers of this path that are not garbage. */
         if (state.gcKeepOutputs) {
-            PathSet derivers = findDerivers(state, path);
+            PathSet derivers = queryValidDerivers(path);
             foreach (PathSet::iterator, deriver, derivers) {
                 /* Break an infinite recursion if gc-keep-derivations
                    and gc-keep-outputs are both set by tentatively
@@ -567,7 +518,7 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
     }
 
     /* The path is garbage, so delete it. */
-    if (doDelete(state.options.action)) {
+    if (shouldDelete(state.options.action)) {
         printMsg(lvlInfo, format("deleting `%1%'") % path);
 
         unsigned long long bytesFreed, blocksFreed;
@@ -613,6 +564,15 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     
     state.gcKeepOutputs = queryBoolSetting("gc-keep-outputs", false);
     state.gcKeepDerivations = queryBoolSetting("gc-keep-derivations", true);
+
+    /* Using `--ignore-liveness' with `--delete' can have unintended
+       consequences if `gc-keep-outputs' or `gc-keep-derivations' are
+       true (the garbage collector will recurse into deleting the
+       outputs or derivers, respectively).  So disable them. */
+    if (options.action == GCOptions::gcDeleteSpecific && options.ignoreLiveness) {
+        state.gcKeepOutputs = false;
+        state.gcKeepDerivations = false;
+    }
     
     /* Acquire the global GC root.  This prevents
        a) New roots from being added.
@@ -667,7 +627,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
         vector<Path> entries_(entries.begin(), entries.end());
         random_shuffle(entries_.begin(), entries_.end());
 
-        if (doDelete(state.options.action))
+        if (shouldDelete(state.options.action))
             printMsg(lvlError, format("deleting garbage..."));
         else
             printMsg(lvlError, format("determining live/dead paths..."));
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 75d2f69c2b72..7069d104aae4 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -20,7 +20,7 @@ string nixBinDir = "/UNINIT";
 bool keepFailed = false;
 bool keepGoing = false;
 bool tryFallback = false;
-Verbosity buildVerbosity = lvlInfo;
+Verbosity buildVerbosity = lvlError;
 unsigned int maxBuildJobs = 1;
 unsigned int buildCores = 1;
 bool readOnlyMode = false;
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index f430492fd407..c0c75e34d502 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -4,6 +4,7 @@
 #include "archive.hh"
 #include "pathlocks.hh"
 #include "worker-protocol.hh"
+#include "derivations.hh"
     
 #include <iostream>
 #include <algorithm>
@@ -16,10 +17,137 @@
 #include <errno.h>
 #include <stdio.h>
 
+#include <sqlite3.h>
+
 
 namespace nix {
 
     
+class SQLiteError : public Error
+{
+public:
+    SQLiteError(sqlite3 * db, const format & f)
+        : Error(format("%1%: %2%") % f.str() % sqlite3_errmsg(db))
+    {
+    }
+};
+
+
+SQLite::~SQLite()
+{
+    try {
+        if (db && sqlite3_close(db) != SQLITE_OK)
+            throw SQLiteError(db, "closing database");
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void SQLiteStmt::create(sqlite3 * db, const string & s)
+{
+    checkInterrupt();
+    assert(!stmt);
+    if (sqlite3_prepare_v2(db, s.c_str(), -1, &stmt, 0) != SQLITE_OK)
+        throw SQLiteError(db, "creating statement");
+    this->db = db;
+}
+
+
+void SQLiteStmt::reset()
+{
+    assert(stmt);
+    if (sqlite3_reset(stmt) != SQLITE_OK)
+        throw SQLiteError(db, "resetting statement");
+    curArg = 1;
+}
+
+
+SQLiteStmt::~SQLiteStmt()
+{
+    try {
+        if (stmt && sqlite3_finalize(stmt) != SQLITE_OK)
+            throw SQLiteError(db, "finalizing statement");
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void SQLiteStmt::bind(const string & value)
+{
+    if (sqlite3_bind_text(stmt, curArg++, value.c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+        throw SQLiteError(db, "binding argument");
+}
+
+
+void SQLiteStmt::bind(int value)
+{
+    if (sqlite3_bind_int(stmt, curArg++, value) != SQLITE_OK)
+        throw SQLiteError(db, "binding argument");
+}
+
+
+void SQLiteStmt::bind()
+{
+    if (sqlite3_bind_null(stmt, curArg++) != SQLITE_OK)
+        throw SQLiteError(db, "binding argument");
+}
+
+
+/* Helper class to ensure that prepared statements are reset when
+   leaving the scope that uses them.  Unfinished prepared statements
+   prevent transactions from being aborted, and can cause locks to be
+   kept when they should be released. */
+struct SQLiteStmtUse
+{
+    SQLiteStmt & stmt;
+    SQLiteStmtUse(SQLiteStmt & stmt) : stmt(stmt)
+    {
+        stmt.reset();
+    }
+    ~SQLiteStmtUse()
+    {
+        try {
+            stmt.reset();
+        } catch (...) {
+            ignoreException();
+        }
+    }
+};
+
+
+struct SQLiteTxn 
+{
+    bool active;
+    sqlite3 * db;
+    
+    SQLiteTxn(sqlite3 * db) : active(false) {
+        this->db = db;
+        if (sqlite3_exec(db, "begin;", 0, 0, 0) != SQLITE_OK)
+            throw SQLiteError(db, "starting transaction");
+        active = true;
+    }
+
+    void commit() 
+    {
+        if (sqlite3_exec(db, "commit;", 0, 0, 0) != SQLITE_OK)
+            throw SQLiteError(db, "committing transaction");
+        active = false;
+    }
+    
+    ~SQLiteTxn() 
+    {
+        try {
+            if (active && sqlite3_exec(db, "rollback;", 0, 0, 0) != SQLITE_OK)
+                throw SQLiteError(db, "aborting transaction");
+        } catch (...) {
+            ignoreException();
+        }
+    }
+};
+
+
 void checkStoreNotSymlink()
 {
     if (getEnv("NIX_IGNORE_SYMLINK_STORE") == "1") return;
@@ -44,13 +172,13 @@ LocalStore::LocalStore()
     
     schemaPath = nixDBPath + "/schema";
     
-    if (readOnlyMode) return;
+    if (readOnlyMode) {
+        openDB(false);
+        return;
+    }
 
     /* Create missing state directories if they don't already exist. */
     createDirs(nixStore);
-    createDirs(nixDBPath + "/info");
-    createDirs(nixDBPath + "/referrer");
-    createDirs(nixDBPath + "/failed");
     Path profilesDir = nixStateDir + "/profiles";
     createDirs(nixStateDir + "/profiles");
     createDirs(nixStateDir + "/temproots");
@@ -63,12 +191,15 @@ LocalStore::LocalStore()
   
     checkStoreNotSymlink();
 
+    /* Acquire the big fat lock in shared mode to make sure that no
+       schema upgrade is in progress. */
     try {
         Path globalLockPath = nixDBPath + "/big-lock";
         globalLock = openLockFile(globalLockPath.c_str(), true);
     } catch (SysError & e) {
         if (e.errNo != EACCES) throw;
         readOnlyMode = true;
+        openDB(false);
         return;
     }
     
@@ -76,33 +207,55 @@ LocalStore::LocalStore()
         printMsg(lvlError, "waiting for the big Nix store lock...");
         lockFile(globalLock, ltRead, true);
     }
-    
+
+    /* Check the current database schema and if necessary do an
+       upgrade.  */
     int curSchema = getSchema();
     if (curSchema > nixSchemaVersion)
         throw Error(format("current Nix store schema is version %1%, but I only support %2%")
             % curSchema % nixSchemaVersion);
-    if (curSchema == 0) { /* new store */
-        curSchema = nixSchemaVersion; 
+    
+    else if (curSchema == 0) { /* new store */
+        curSchema = nixSchemaVersion;
+        openDB(true);
         writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
     }
-    if (curSchema == 1) throw Error("your Nix store is no longer supported");
-    if (curSchema < nixSchemaVersion) upgradeStore12();
+    
+    else if (curSchema < nixSchemaVersion) {
+        if (curSchema < 5)
+            throw Error(
+                "Your Nix store has a database in Berkeley DB format,\n"
+                "which is no longer supported. To convert to the new format,\n"
+                "please upgrade Nix to version 0.12 first.");
+        
+        if (!lockFile(globalLock, ltWrite, false)) {
+            printMsg(lvlError, "waiting for exclusive access to the Nix store...");
+            lockFile(globalLock, ltWrite, true);
+        }
+
+        /* Get the schema version again, because another process may
+           have performed the upgrade already. */
+        curSchema = getSchema();
+
+        if (curSchema < 6) upgradeStore6();
+
+        writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
 
-    doFsync = queryBoolSetting("fsync-metadata", false);
+        lockFile(globalLock, ltRead, true);
+    }
+    
+    else openDB(false);
 }
 
 
 LocalStore::~LocalStore()
 {
     try {
-        flushDelayedUpdates();
-
         foreach (RunningSubstituters::iterator, i, runningSubstituters) {
             i->second.to.close();
             i->second.from.close();
             i->second.pid.wait(true);
         }
-                
     } catch (...) {
         ignoreException();
     }
@@ -121,6 +274,89 @@ int LocalStore::getSchema()
 }
 
 
+void LocalStore::openDB(bool create)
+{
+    /* Open the Nix database. */
+    if (sqlite3_open_v2((nixDBPath + "/db.sqlite").c_str(), &db.db,
+            SQLITE_OPEN_READWRITE | (create ? SQLITE_OPEN_CREATE : 0), 0) != SQLITE_OK)
+        throw Error("cannot open SQLite database");
+
+    if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
+        throw SQLiteError(db, "setting timeout");
+
+    if (sqlite3_exec(db, "pragma foreign_keys = 1;", 0, 0, 0) != SQLITE_OK)
+        throw SQLiteError(db, "enabling foreign keys");
+
+    /* !!! check whether sqlite has been built with foreign key
+       support */
+    
+    /* Whether SQLite should fsync().  "Normal" synchronous mode
+       should be safe enough.  If the user asks for it, don't sync at
+       all.  This can cause database corruption if the system
+       crashes. */
+    string syncMode = queryBoolSetting("fsync-metadata", true) ? "normal" : "off";
+    if (sqlite3_exec(db, ("pragma synchronous = " + syncMode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
+        throw SQLiteError(db, "setting synchronous mode");
+
+    /* Set the SQLite journal mode.  WAL mode is fastest, but doesn't
+       seem entirely stable at the moment (Oct. 2010).  Thus, use
+       truncate mode by default. */
+    string mode = queryBoolSetting("use-sqlite-wal", false) ? "wal" : "truncate";
+    string prevMode;
+    {
+        SQLiteStmt stmt;
+        stmt.create(db, "pragma main.journal_mode;");
+        if (sqlite3_step(stmt) != SQLITE_ROW)
+            throw SQLiteError(db, "querying journal mode");
+        prevMode = string((const char *) sqlite3_column_text(stmt, 0));
+    }
+    if (prevMode != mode &&
+        sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
+        throw SQLiteError(db, "setting journal mode");
+
+    /* Increase the auto-checkpoint interval to 8192 pages.  This
+       seems enough to ensure that instantiating the NixOS system
+       derivation is done in a single fsync(). */
+    if (sqlite3_exec(db, "pragma wal_autocheckpoint = 8192;", 0, 0, 0) != SQLITE_OK)
+        throw SQLiteError(db, "setting autocheckpoint interval");
+    
+    /* Initialise the database schema, if necessary. */
+    if (create) {
+#include "schema.sql.hh"
+        if (sqlite3_exec(db, (const char *) schema, 0, 0, 0) != SQLITE_OK)
+            throw SQLiteError(db, "initialising database schema");
+    }
+
+    /* Prepare SQL statements. */
+    stmtRegisterValidPath.create(db,
+        "insert into ValidPaths (path, hash, registrationTime, deriver) values (?, ?, ?, ?);");
+    stmtAddReference.create(db,
+        "insert or replace into Refs (referrer, reference) values (?, ?);");
+    stmtQueryPathInfo.create(db,
+        "select id, hash, registrationTime, deriver from ValidPaths where path = ?;");
+    stmtQueryReferences.create(db,
+        "select path from Refs join ValidPaths on reference = id where referrer = ?;");
+    stmtQueryReferrers.create(db,
+        "select path from Refs join ValidPaths on referrer = id where reference = (select id from ValidPaths where path = ?);");
+    stmtInvalidatePath.create(db,
+        "delete from ValidPaths where path = ?;");
+    stmtRegisterFailedPath.create(db,
+        "insert into FailedPaths (path, time) values (?, ?);");
+    stmtHasPathFailed.create(db,
+        "select time from FailedPaths where path = ?;");
+    stmtQueryFailedPaths.create(db,
+        "select path from FailedPaths;");
+    stmtClearFailedPath.create(db,
+        "delete from FailedPaths where ?1 = '*' or path = ?1;");
+    stmtAddDerivationOutput.create(db,
+        "insert or replace into DerivationOutputs (drv, id, path) values (?, ?, ?);");
+    stmtQueryValidDerivers.create(db,
+        "select v.id, v.path from DerivationOutputs d join ValidPaths v on d.drv = v.id where d.path = ?;");
+    stmtQueryDerivationOutputs.create(db,
+        "select id, path from DerivationOutputs where drv = ?;");
+}
+
+
 void canonicalisePathMetaData(const Path & path, bool recurse)
 {
     checkInterrupt();
@@ -195,181 +431,133 @@ void canonicalisePathMetaData(const Path & path)
 }
 
 
-static Path infoFileFor(const Path & path)
-{
-    string baseName = baseNameOf(path);
-    return (format("%1%/info/%2%") % nixDBPath % baseName).str();
-}
-
-
-static Path referrersFileFor(const Path & path)
+void LocalStore::registerValidPath(const Path & path,
+    const Hash & hash, const PathSet & references,
+    const Path & deriver)
 {
-    string baseName = baseNameOf(path);
-    return (format("%1%/referrer/%2%") % nixDBPath % baseName).str();
+    ValidPathInfo info;
+    info.path = path;
+    info.hash = hash;
+    info.references = references;
+    info.deriver = deriver;
+    registerValidPath(info);
 }
 
 
-static Path failedFileFor(const Path & path)
+unsigned long long LocalStore::addValidPath(const ValidPathInfo & info)
 {
-    string baseName = baseNameOf(path);
-    return (format("%1%/failed/%2%") % nixDBPath % baseName).str();
-}
-
+    SQLiteStmtUse use(stmtRegisterValidPath);
+    stmtRegisterValidPath.bind(info.path);
+    stmtRegisterValidPath.bind("sha256:" + printHash(info.hash));
+    stmtRegisterValidPath.bind(info.registrationTime);
+    if (info.deriver != "")
+        stmtRegisterValidPath.bind(info.deriver);
+    else
+        stmtRegisterValidPath.bind(); // null
+    if (sqlite3_step(stmtRegisterValidPath) != SQLITE_DONE)
+        throw SQLiteError(db, format("registering valid path `%1%' in database") % info.path);
+    unsigned long long id = sqlite3_last_insert_rowid(db);
+
+    /* If this is a derivation, then store the derivation outputs in
+       the database.  This is useful for the garbage collector: it can
+       efficiently query whether a path is an output of some
+       derivation. */
+    if (isDerivation(info.path)) {
+        Derivation drv = parseDerivation(readFile(info.path));
+        foreach (DerivationOutputs::iterator, i, drv.outputs) {
+            SQLiteStmtUse use(stmtAddDerivationOutput);
+            stmtAddDerivationOutput.bind(id);
+            stmtAddDerivationOutput.bind(i->first);
+            stmtAddDerivationOutput.bind(i->second.path);
+            if (sqlite3_step(stmtAddDerivationOutput) != SQLITE_DONE)
+                throw SQLiteError(db, format("adding derivation output for `%1%' in database") % info.path);
+        }
+    }
 
-static Path tmpFileForAtomicUpdate(const Path & path)
-{
-    return (format("%1%/.%2%.%3%") % dirOf(path) % getpid() % baseNameOf(path)).str();
+    return id;
 }
 
 
-void LocalStore::appendReferrer(const Path & from, const Path & to, bool lock)
+void LocalStore::addReference(unsigned long long referrer, unsigned long long reference)
 {
-    Path referrersFile = referrersFileFor(from);
-    
-    PathLocks referrersLock;
-    if (lock) {
-        referrersLock.lockPaths(singleton<PathSet, Path>(referrersFile));
-        referrersLock.setDeletion(true);
-    }
-
-    AutoCloseFD fd = open(referrersFile.c_str(), O_WRONLY | O_APPEND | O_CREAT, 0666);
-    if (fd == -1) throw SysError(format("opening file `%1%'") % referrersFile);
-    
-    string s = " " + to;
-    writeFull(fd, (const unsigned char *) s.c_str(), s.size());
-
-    if (doFsync) fsync(fd);
+    SQLiteStmtUse use(stmtAddReference);
+    stmtAddReference.bind(referrer);
+    stmtAddReference.bind(reference);
+    if (sqlite3_step(stmtAddReference) != SQLITE_DONE)
+        throw SQLiteError(db, "adding reference to database");
 }
 
 
-/* Atomically update the referrers file.  If `purge' is true, the set
-   of referrers is set to `referrers'.  Otherwise, the current set of
-   referrers is purged of invalid paths. */
-void LocalStore::rewriteReferrers(const Path & path, bool purge, PathSet referrers)
+void LocalStore::registerValidPath(const ValidPathInfo & info)
 {
-    Path referrersFile = referrersFileFor(path);
-    
-    PathLocks referrersLock(singleton<PathSet, Path>(referrersFile));
-    referrersLock.setDeletion(true);
-
-    if (purge)
-        /* queryReferrers() purges invalid paths, so that's all we
-           need. */
-        queryReferrers(path, referrers);
-
-    Path tmpFile = tmpFileForAtomicUpdate(referrersFile);
-    
-    AutoCloseFD fd = open(tmpFile.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
-    if (fd == -1) throw SysError(format("opening file `%1%'") % referrersFile);
-    
-    string s;
-    foreach (PathSet::const_iterator, i, referrers) {
-        s += " "; s += *i;
-    }
+    assert(info.hash.type == htSHA256);
+    ValidPathInfo info2(info);
+    if (info2.registrationTime == 0) info2.registrationTime = time(0);
     
-    writeFull(fd, (const unsigned char *) s.c_str(), s.size());
-
-    if (doFsync) fsync(fd);
+    SQLiteTxn txn(db);
     
-    fd.close(); /* for Windows; can't rename open file */
+    unsigned long long id = addValidPath(info2);
 
-    if (rename(tmpFile.c_str(), referrersFile.c_str()) == -1)
-        throw SysError(format("cannot rename `%1%' to `%2%'") % tmpFile % referrersFile);
+    foreach (PathSet::const_iterator, i, info2.references)
+        addReference(id, queryValidPathId(*i));
+        
+    txn.commit();
 }
 
 
-void LocalStore::flushDelayedUpdates()
+void LocalStore::registerFailedPath(const Path & path)
 {
-    foreach (PathSet::iterator, i, delayedUpdates) {
-        rewriteReferrers(*i, true, PathSet());
-    }
-    delayedUpdates.clear();
+    if (hasPathFailed(path)) return;
+    SQLiteStmtUse use(stmtRegisterFailedPath);
+    stmtRegisterFailedPath.bind(path);
+    stmtRegisterFailedPath.bind(time(0));
+    if (sqlite3_step(stmtRegisterFailedPath) != SQLITE_DONE)
+        throw SQLiteError(db, format("registering failed path `%1%'") % path);
 }
 
 
-void LocalStore::registerValidPath(const Path & path,
-    const Hash & hash, const PathSet & references,
-    const Path & deriver)
+bool LocalStore::hasPathFailed(const Path & path)
 {
-    ValidPathInfo info;
-    info.path = path;
-    info.hash = hash;
-    info.references = references;
-    info.deriver = deriver;
-    registerValidPath(info);
+    SQLiteStmtUse use(stmtHasPathFailed);
+    stmtHasPathFailed.bind(path);
+    int res = sqlite3_step(stmtHasPathFailed);
+    if (res != SQLITE_DONE && res != SQLITE_ROW)
+        throw SQLiteError(db, "querying whether path failed");
+    return res == SQLITE_ROW;
 }
 
 
-void LocalStore::registerValidPath(const ValidPathInfo & info, bool ignoreValidity)
+PathSet LocalStore::queryFailedPaths()
 {
-    Path infoFile = infoFileFor(info.path);
-
-    ValidPathInfo oldInfo;
-    if (pathExists(infoFile)) oldInfo = queryPathInfo(info.path);
-
-    /* Note that it's possible for infoFile to already exist. */
-
-    /* Acquire a lock on each referrer file.  This prevents those
-       paths from being invalidated.  (It would be a violation of the
-       store invariants if we registered info.path as valid while some
-       of its references are invalid.)  NB: there can be no deadlock
-       here since we're acquiring the locks in sorted order. */
-    PathSet lockNames;
-    foreach (PathSet::const_iterator, i, info.references)
-        if (*i != info.path) lockNames.insert(referrersFileFor(*i));
-    PathLocks referrerLocks(lockNames);
-    referrerLocks.setDeletion(true);
-        
-    string refs;
-    foreach (PathSet::const_iterator, i, info.references) {
-        if (!refs.empty()) refs += " ";
-        refs += *i;
-
-        if (!ignoreValidity && *i != info.path && !isValidPath(*i))
-            throw Error(format("cannot register `%1%' as valid, because its reference `%2%' isn't valid")
-                % info.path % *i);
-
-        /* Update the referrer mapping for *i.  This must be done
-           before the info file is written to maintain the invariant
-           that if `path' is a valid path, then all its references
-           have referrer mappings back to `path'.  A " " is prefixed
-           to separate it from the previous entry.  It's not suffixed
-           to deal with interrupted partial writes to this file. */
-        if (oldInfo.references.find(*i) == oldInfo.references.end())
-            appendReferrer(*i, info.path, false);
+    SQLiteStmtUse use(stmtQueryFailedPaths);
+
+    PathSet res;
+    int r;
+    while ((r = sqlite3_step(stmtQueryFailedPaths)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryFailedPaths, 0);
+        assert(s);
+        res.insert(s);
     }
 
-    assert(info.hash.type == htSHA256);
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, "error querying failed paths");
 
-    string s = (format(
-        "Hash: sha256:%1%\n"
-        "References: %2%\n"
-        "Deriver: %3%\n"
-        "Registered-At: %4%\n")
-        % printHash(info.hash) % refs % info.deriver %
-        (oldInfo.registrationTime ? oldInfo.registrationTime : time(0))).str();
-
-    /* Atomically rewrite the info file. */
-    Path tmpFile = tmpFileForAtomicUpdate(infoFile);
-    writeFile(tmpFile, s, doFsync);
-    if (rename(tmpFile.c_str(), infoFile.c_str()) == -1)
-        throw SysError(format("cannot rename `%1%' to `%2%'") % tmpFile % infoFile);
-
-    pathInfoCache[info.path] = info;
+    return res;
 }
 
 
-void LocalStore::registerFailedPath(const Path & path)
+void LocalStore::clearFailedPaths(const PathSet & paths)
 {
-    /* Write an empty file in the .../failed directory to denote the
-       failure of the builder for `path'. */
-    writeFile(failedFileFor(path), "");
-}
+    SQLiteTxn txn(db);
 
+    foreach (PathSet::const_iterator, i, paths) {
+        SQLiteStmtUse use(stmtClearFailedPath);
+        stmtClearFailedPath.bind(*i);
+        if (sqlite3_step(stmtClearFailedPath) != SQLITE_DONE)
+            throw SQLiteError(db, format("clearing failed path `%1%' in database") % *i);
+    }
 
-bool LocalStore::hasPathFailed(const Path & path)
-{
-    return pathExists(failedFileFor(path));
+    txn.commit();
 }
 
 
@@ -387,91 +575,91 @@ Hash parseHashField(const Path & path, const string & s)
 }
 
 
-ValidPathInfo LocalStore::queryPathInfo(const Path & path, bool ignoreErrors)
+ValidPathInfo LocalStore::queryPathInfo(const Path & path)
 {
-    ValidPathInfo res;
-    res.path = path;
+    ValidPathInfo info;
+    info.path = path;
 
     assertStorePath(path);
 
-    if (!isValidPath(path))
-        throw Error(format("path `%1%' is not valid") % path);
+    /* Get the path info. */
+    SQLiteStmtUse use1(stmtQueryPathInfo);
 
-    std::map<Path, ValidPathInfo>::iterator lookup = pathInfoCache.find(path);
-    if (lookup != pathInfoCache.end()) return lookup->second;
+    stmtQueryPathInfo.bind(path);
     
-    /* Read the info file. */
-    Path infoFile = infoFileFor(path);
-    if (!pathExists(infoFile))
-        throw Error(format("path `%1%' is not valid") % path);
-    string info = readFile(infoFile);
+    int r = sqlite3_step(stmtQueryPathInfo);
+    if (r == SQLITE_DONE) throw Error(format("path `%1%' is not valid") % path);
+    if (r != SQLITE_ROW) throw SQLiteError(db, "querying path in database");
 
-    /* Parse it. */
-    Strings lines = tokenizeString(info, "\n");
+    info.id = sqlite3_column_int(stmtQueryPathInfo, 0);
 
-    foreach (Strings::iterator, i, lines) {
-        string::size_type p = i->find(':');
-        if (p == string::npos) {
-            if (!ignoreErrors)
-                throw Error(format("corrupt line in `%1%': %2%") % infoFile % *i);
-            continue; /* bad line */
-        }
-        string name(*i, 0, p);
-        string value(*i, p + 2);
-        if (name == "References") {
-            Strings refs = tokenizeString(value, " ");
-            res.references = PathSet(refs.begin(), refs.end());
-        } else if (name == "Deriver") {
-            res.deriver = value;
-        } else if (name == "Hash") {
-            try {
-                res.hash = parseHashField(path, value);
-            } catch (Error & e) {
-                if (!ignoreErrors) throw;
-                printMsg(lvlError, format("cannot parse hash field in `%1%': %2%") % infoFile % e.msg());
-            }
-        } else if (name == "Registered-At") {
-            int n = 0;
-            string2Int(value, n);
-            res.registrationTime = n;
-        }
+    const char * s = (const char *) sqlite3_column_text(stmtQueryPathInfo, 1);
+    assert(s);
+    info.hash = parseHashField(path, s);
+    
+    info.registrationTime = sqlite3_column_int(stmtQueryPathInfo, 2);
+
+    s = (const char *) sqlite3_column_text(stmtQueryPathInfo, 3);
+    if (s) info.deriver = s;
+
+    /* Get the references. */
+    SQLiteStmtUse use2(stmtQueryReferences);
+
+    stmtQueryReferences.bind(info.id);
+
+    while ((r = sqlite3_step(stmtQueryReferences)) == SQLITE_ROW) {
+        s = (const char *) sqlite3_column_text(stmtQueryReferences, 0);
+        assert(s);
+        info.references.insert(s);
     }
 
-    return pathInfoCache[path] = res;
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, format("error getting references of `%1%'") % path);
+
+    return info;
 }
 
 
-bool LocalStore::isValidPath(const Path & path)
+unsigned long long LocalStore::queryValidPathId(const Path & path)
 {
-    /* Files in the info directory starting with a `.' are temporary
-       files. */
-    if (baseNameOf(path).at(0) == '.') return false;
+    SQLiteStmtUse use(stmtQueryPathInfo);
+    stmtQueryPathInfo.bind(path);
+    int res = sqlite3_step(stmtQueryPathInfo);
+    if (res == SQLITE_ROW) return sqlite3_column_int(stmtQueryPathInfo, 0);
+    if (res == SQLITE_DONE) throw Error(format("path `%1%' is not valid") % path);
+    throw SQLiteError(db, "querying path in database");
+}
 
-    /* A path is valid if its info file exists and has a non-zero
-       size.  (The non-zero size restriction is to be robust to
-       certain kinds of filesystem corruption, particularly with
-       ext4.) */
-    Path infoFile = infoFileFor(path);
 
-    struct stat st;
-    if (lstat(infoFile.c_str(), &st)) {
-        if (errno == ENOENT) return false;
-        throw SysError(format("getting status of `%1%'") % infoFile);
-    }
-
-    if (st.st_size == 0) return false;
-    
-    return true;
+bool LocalStore::isValidPath(const Path & path)
+{
+    SQLiteStmtUse use(stmtQueryPathInfo);
+    stmtQueryPathInfo.bind(path);
+    int res = sqlite3_step(stmtQueryPathInfo);
+    if (res != SQLITE_DONE && res != SQLITE_ROW)
+        throw SQLiteError(db, "querying path in database");
+    return res == SQLITE_ROW;
 }
 
 
 PathSet LocalStore::queryValidPaths()
 {
-    PathSet paths;
-    Strings entries = readDirectory(nixDBPath + "/info");
-    foreach (Strings::iterator, i, entries)
-        if (i->at(0) != '.') paths.insert(nixStore + "/" + *i);
-    return paths;
+    SQLiteStmt stmt;
+    stmt.create(db, "select path from ValidPaths");
+    
+    PathSet res;
+    
+    int r;
+    while ((r = sqlite3_step(stmt)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmt, 0);
+        assert(s);
+        res.insert(s);
+    }
+
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, "error getting valid paths");
+
+    return res;
 }
 
 
@@ -483,45 +671,73 @@ void LocalStore::queryReferences(const Path & path,
 }
 
 
-bool LocalStore::queryReferrersInternal(const Path & path, PathSet & referrers)
+void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
 {
-    bool allValid = true;
-    
-    if (!isValidPath(path))
-        throw Error(format("path `%1%' is not valid") % path);
+    assertStorePath(path);
 
-    /* No locking is necessary here: updates are only done by
-       appending or by atomically replacing the file.  When appending,
-       there is a possibility that we see a partial entry, but it will
-       just be filtered out below (the partially written path will not
-       be valid, so it will be ignored). */
+    SQLiteStmtUse use(stmtQueryReferrers);
 
-    Path referrersFile = referrersFileFor(path);
-    if (!pathExists(referrersFile)) return true;
-    
-    AutoCloseFD fd = open(referrersFile.c_str(), O_RDONLY);
-    if (fd == -1) throw SysError(format("opening file `%1%'") % referrersFile);
+    stmtQueryReferrers.bind(path);
+
+    int r;
+    while ((r = sqlite3_step(stmtQueryReferrers)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryReferrers, 0);
+        assert(s);
+        referrers.insert(s);
+    }
 
-    Paths refs = tokenizeString(readFile(fd), " ");
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, format("error getting references of `%1%'") % path);
+}
 
-    foreach (Paths::iterator, i, refs)
-        /* Referrers can be invalid (see registerValidPath() for the
-           invariant), so we only return one if it is valid. */
-        if (isStorePath(*i) && isValidPath(*i)) referrers.insert(*i); else allValid = false;
 
-    return allValid;
+Path LocalStore::queryDeriver(const Path & path)
+{
+    return queryPathInfo(path).deriver;
 }
 
 
-void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
+PathSet LocalStore::queryValidDerivers(const Path & path)
 {
-    queryReferrersInternal(path, referrers);
+    assertStorePath(path);
+
+    SQLiteStmtUse use(stmtQueryValidDerivers);
+    stmtQueryValidDerivers.bind(path);
+
+    PathSet derivers;
+    int r;
+    while ((r = sqlite3_step(stmtQueryValidDerivers)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryValidDerivers, 1);
+        assert(s);
+        derivers.insert(s);
+    }
+    
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, format("error getting valid derivers of `%1%'") % path);
+    
+    return derivers;
 }
 
 
-Path LocalStore::queryDeriver(const Path & path)
+PathSet LocalStore::queryDerivationOutputs(const Path & path)
 {
-    return queryPathInfo(path).deriver;
+    SQLiteTxn txn(db);
+    
+    SQLiteStmtUse use(stmtQueryDerivationOutputs);
+    stmtQueryDerivationOutputs.bind(queryValidPathId(path));
+    
+    PathSet outputs;
+    int r;
+    while ((r = sqlite3_step(stmtQueryDerivationOutputs)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryDerivationOutputs, 1);
+        assert(s);
+        outputs.insert(s);
+    }
+    
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, format("error getting outputs of `%1%'") % path);
+
+    return outputs;
 }
 
 
@@ -635,39 +851,22 @@ Hash LocalStore::queryPathHash(const Path & path)
 }
 
 
-static void dfsVisit(std::map<Path, ValidPathInfo> & infos,
-    const Path & path, PathSet & visited, Paths & sorted)
-{
-    if (visited.find(path) != visited.end()) return;
-    visited.insert(path);
-
-    ValidPathInfo & info(infos[path]);
-    
-    foreach (PathSet::iterator, i, info.references)
-        if (infos.find(*i) != infos.end())
-            dfsVisit(infos, *i, visited, sorted);
-
-    sorted.push_back(path);
-}
-
-
 void LocalStore::registerValidPaths(const ValidPathInfos & infos)
 {
-    std::map<Path, ValidPathInfo> infosMap;
+    SQLiteTxn txn(db);
     
-    /* Sort the paths topologically under the references relation, so
-       that if path A is referenced by B, then A is registered before
-       B. */
-    foreach (ValidPathInfos::const_iterator, i, infos)
-        infosMap[i->path] = *i;
-
-    PathSet visited;
-    Paths sorted;
     foreach (ValidPathInfos::const_iterator, i, infos)
-        dfsVisit(infosMap, i->path, visited, sorted);
+        /* !!! Maybe the registration info should be updated if the
+           path is already valid. */
+        if (!isValidPath(i->path)) addValidPath(*i);
+
+    foreach (ValidPathInfos::const_iterator, i, infos) {
+        unsigned long long referrer = queryValidPathId(i->path);
+        foreach (PathSet::iterator, j, i->references)
+            addReference(referrer, queryValidPathId(*j));
+    }
 
-    foreach (Paths::iterator, i, sorted)
-        registerValidPath(infosMap[*i]);
+    txn.commit();
 }
 
 
@@ -677,43 +876,15 @@ void LocalStore::invalidatePath(const Path & path)
 {
     debug(format("invalidating path `%1%'") % path);
 
-    ValidPathInfo info;
+    SQLiteStmtUse use(stmtInvalidatePath);
 
-    if (pathExists(infoFileFor(path))) {
-        info = queryPathInfo(path);
+    stmtInvalidatePath.bind(path);
 
-        /* Remove the info file. */
-        Path p = infoFileFor(path);
-        if (unlink(p.c_str()) == -1)
-            throw SysError(format("unlinking `%1%'") % p);
-    }
+    if (sqlite3_step(stmtInvalidatePath) != SQLITE_DONE)
+        throw SQLiteError(db, format("invalidating path `%1%' in database") % path);
 
-    /* Remove the referrers file for `path'. */
-    Path p = referrersFileFor(path);
-    if (pathExists(p) && unlink(p.c_str()) == -1)
-        throw SysError(format("unlinking `%1%'") % p);
-
-    /* Clear `path' from the info cache. */
-    pathInfoCache.erase(path);
-    delayedUpdates.erase(path);
-
-    /* Cause the referrer files for each path referenced by this one
-       to be updated.  This has to happen after removing the info file
-       to preserve the invariant (see registerValidPath()).
-
-       The referrer files are updated lazily in flushDelayedUpdates()
-       to prevent quadratic performance in the garbage collector
-       (i.e., when N referrers to some path X are deleted, we have to
-       rewrite the referrers file for X N times, causing O(N^2) I/O).
-
-       What happens if we die before the referrer file can be updated?
-       That's not a problem, because stale (invalid) entries in the
-       referrer file are ignored by queryReferrers().  Thus a referrer
-       file is allowed to have stale entries; removing them is just an
-       optimisation.  verifyStore() gets rid of them eventually.
-    */
-    foreach (PathSet::iterator, i, info.references)
-        if (*i != path) delayedUpdates.insert(*i);
+    /* Note that the foreign key constraints on the Refs table take
+       care of deleting the references entries for `path'. */
 }
 
 
@@ -815,16 +986,19 @@ struct HashAndWriteSink : Sink
 {
     Sink & writeSink;
     HashSink hashSink;
-    bool hashing;
     HashAndWriteSink(Sink & writeSink) : writeSink(writeSink), hashSink(htSHA256)
     {
-        hashing = true;
     }
     virtual void operator ()
         (const unsigned char * data, unsigned int len)
     {
         writeSink(data, len);
-        if (hashing) hashSink(data, len);
+        hashSink(data, len);
+    }
+    Hash currentHash()
+    {
+        HashSink hashSinkClone(hashSink);
+        return hashSinkClone.finish();
     }
 };
 
@@ -855,6 +1029,15 @@ void LocalStore::exportPath(const Path & path, bool sign,
     
     dumpPath(path, hashAndWriteSink);
 
+    /* Refuse to export paths that have changed.  This prevents
+       filesystem corruption from spreading to other machines.
+       Don't complain if the stored hash is zero (unknown). */
+    Hash hash = hashAndWriteSink.currentHash();
+    Hash storedHash = queryPathHash(path);
+    if (hash != storedHash && storedHash != Hash(storedHash.type))
+        throw Error(format("hash of path `%1%' has changed from `%2%' to `%3%'!") % path
+            % printHash(storedHash) % printHash(hash));
+
     writeInt(EXPORT_MAGIC, hashAndWriteSink);
 
     writeString(path, hashAndWriteSink);
@@ -867,14 +1050,11 @@ void LocalStore::exportPath(const Path & path, bool sign,
     writeString(deriver, hashAndWriteSink);
 
     if (sign) {
-        Hash hash = hashAndWriteSink.hashSink.finish();
-        hashAndWriteSink.hashing = false;
-
+        Hash hash = hashAndWriteSink.currentHash();
+ 
         writeInt(1, hashAndWriteSink);
         
         Path tmpDir = createTempDir();
-        PathLocks tmpDirLock(singleton<PathSet, Path>(tmpDir));
-        tmpDirLock.setDeletion(true);
         AutoDelete delTmp(tmpDir);
         Path hashFile = tmpDir + "/hash";
         writeFile(hashFile, printHash(hash));
@@ -916,6 +1096,22 @@ struct HashAndReadSource : Source
 };
 
 
+/* Create a temporary directory in the store that won't be
+   garbage-collected. */
+Path LocalStore::createTempDirInStore()
+{
+    Path tmpDir;
+    do {
+        /* There is a slight possibility that `tmpDir' gets deleted by
+           the GC between createTempDir() and addTempRoot(), so repeat
+           until `tmpDir' exists. */
+        tmpDir = createTempDir(nixStore);
+        addTempRoot(tmpDir);
+    } while (!pathExists(tmpDir));
+    return tmpDir;
+}
+
+
 Path LocalStore::importPath(bool requireSignature, Source & source)
 {
     HashAndReadSource hashAndReadSource(source);
@@ -923,10 +1119,8 @@ Path LocalStore::importPath(bool requireSignature, Source & source)
     /* We don't yet know what store path this archive contains (the
        store path follows the archive data proper), and besides, we
        don't know yet whether the signature is valid. */
-    Path tmpDir = createTempDir(nixStore);
-    PathLocks tmpDirLock(singleton<PathSet, Path>(tmpDir));
-    tmpDirLock.setDeletion(true);
-    AutoDelete delTmp(tmpDir); /* !!! could be GC'ed! */
+    Path tmpDir = createTempDirInStore();
+    AutoDelete delTmp(tmpDir);
     Path unpacked = tmpDir + "/unpacked";
 
     restorePath(unpacked, hashAndReadSource);
@@ -1025,12 +1219,9 @@ void LocalStore::deleteFromStore(const Path & path, unsigned long long & bytesFr
 
     assertStorePath(path);
 
+    SQLiteTxn txn(db);
+
     if (isValidPath(path)) {
-        /* Acquire a lock on the referrers file to prevent new
-           referrers to this path from appearing while we're deleting
-           it. */
-        PathLocks referrersLock(singleton<PathSet, Path>(referrersFileFor(path)));
-        referrersLock.setDeletion(true);
         PathSet referrers; queryReferrers(path, referrers);
         referrers.erase(path); /* ignore self-references */
         if (!referrers.empty())
@@ -1040,80 +1231,38 @@ void LocalStore::deleteFromStore(const Path & path, unsigned long long & bytesFr
     }
 
     deletePathWrapped(path, bytesFreed, blocksFreed);
+
+    txn.commit();
 }
 
 
 void LocalStore::verifyStore(bool checkContents)
 {
-    /* Check whether all valid paths actually exist. */
-    printMsg(lvlInfo, "checking path existence");
+    printMsg(lvlError, format("reading the Nix store..."));
 
-    PathSet validPaths2 = queryValidPaths(), validPaths;
+    /* Acquire the global GC lock to prevent a garbage collection. */
+    AutoCloseFD fdGCLock = openGCLock(ltWrite);
     
-    foreach (PathSet::iterator, i, validPaths2) {
-        checkInterrupt();
-        if (!isStorePath(*i)) {
-            printMsg(lvlError, format("path `%1%' is not in the Nix store") % *i);
-            invalidatePath(*i);
-        } else if (!pathExists(*i)) {
-            printMsg(lvlError, format("path `%1%' disappeared") % *i);
-            invalidatePath(*i);
-        } else {
-            Path infoFile = infoFileFor(*i);
-            struct stat st;
-            if (lstat(infoFile.c_str(), &st))
-                throw SysError(format("getting status of `%1%'") % infoFile);
-            if (st.st_size == 0) {
-                printMsg(lvlError, format("removing corrupt info file `%1%'") % infoFile);
-                if (unlink(infoFile.c_str()) == -1)
-                    throw SysError(format("unlinking `%1%'") % infoFile);
-            }
-            else validPaths.insert(*i);
-        }
-    }
+    Paths entries = readDirectory(nixStore);
+    PathSet store(entries.begin(), entries.end());
 
+    /* Check whether all valid paths actually exist. */
+    printMsg(lvlInfo, "checking path existence...");
 
-    /* Check the store path meta-information. */
-    printMsg(lvlInfo, "checking path meta-information");
+    PathSet validPaths2 = queryValidPaths(), validPaths, done;
 
-    std::map<Path, PathSet> referrersCache;
-    
-    foreach (PathSet::iterator, i, validPaths) {
-        bool update = false;
-        ValidPathInfo info = queryPathInfo(*i, true);
-
-        /* Check the references: each reference should be valid, and
-           it should have a matching referrer. */
-        foreach (PathSet::iterator, j, info.references) {
-            if (validPaths.find(*j) == validPaths.end()) {
-                printMsg(lvlError, format("incomplete closure: `%1%' needs missing `%2%'")
-                    % *i % *j);
-                /* nothing we can do about it... */
-            } else {
-                if (referrersCache.find(*j) == referrersCache.end())
-                    queryReferrers(*j, referrersCache[*j]);
-                if (referrersCache[*j].find(*i) == referrersCache[*j].end()) {
-                    printMsg(lvlError, format("adding missing referrer mapping from `%1%' to `%2%'")
-                        % *j % *i);
-                    appendReferrer(*j, *i, true);
-                }
-            }
-        }
+    foreach (PathSet::iterator, i, validPaths2)
+        verifyPath(*i, store, done, validPaths);
 
-        /* Check the deriver.  (Note that the deriver doesn't have to
-           be a valid path.) */
-        if (!info.deriver.empty() && !isStorePath(info.deriver)) {
-            info.deriver = "";
-            update = true;
-        }
+    /* Optionally, check the content hashes (slow). */
+    if (checkContents) {
+        printMsg(lvlInfo, "checking hashes...");
 
-        /* Check the content hash (optionally - slow). */
-        if (info.hash.hashSize == 0) {
-            printMsg(lvlError, format("re-hashing `%1%'") % *i);
-            info.hash = hashPath(htSHA256, *i);
-            update = true;
-        } else if (checkContents) {
-            debug(format("checking contents of `%1%'") % *i);
+        foreach (PathSet::iterator, i, validPaths) {
+            ValidPathInfo info = queryPathInfo(*i);
+
+            /* Check the content hash (optionally - slow). */
+            printMsg(lvlTalkative, format("checking contents of `%1%'") % *i);
             Hash current = hashPath(info.hash.type, *i);
             if (current != info.hash) {
                 printMsg(lvlError, format("path `%1%' was modified! "
@@ -1121,67 +1270,129 @@ void LocalStore::verifyStore(bool checkContents)
                     % *i % printHash(info.hash) % printHash(current));
             }
         }
-
-        if (update) registerValidPath(info);
     }
+}
+
 
-    referrersCache.clear();
+void LocalStore::verifyPath(const Path & path, const PathSet & store,
+    PathSet & done, PathSet & validPaths)
+{
+    checkInterrupt();
     
+    if (done.find(path) != done.end()) return;
+    done.insert(path);
+
+    if (!isStorePath(path)) {
+        printMsg(lvlError, format("path `%1%' is not in the Nix store") % path);
+        invalidatePath(path);
+        return;
+    }
 
-    /* Check the referrers. */
-    printMsg(lvlInfo, "checking referrers");
+    if (store.find(baseNameOf(path)) == store.end()) {
+        /* Check any referrers first.  If we can invalidate them
+           first, then we can invalidate this path as well. */
+        bool canInvalidate = true;
+        PathSet referrers; queryReferrers(path, referrers);
+        foreach (PathSet::iterator, i, referrers)
+            if (*i != path) {
+                verifyPath(*i, store, done, validPaths);
+                if (validPaths.find(*i) != validPaths.end())
+                    canInvalidate = false;
+            }
 
-    std::map<Path, PathSet> referencesCache;
-    
-    Strings entries = readDirectory(nixDBPath + "/referrer");
-    foreach (Strings::iterator, i, entries) {
-        Path from = nixStore + "/" + *i;
+        if (canInvalidate) {
+            printMsg(lvlError, format("path `%1%' disappeared, removing from database...") % path);
+            invalidatePath(path);
+        } else
+            printMsg(lvlError, format("path `%1%' disappeared, but it still has valid referrers!") % path);
         
-        if (validPaths.find(from) == validPaths.end()) {
-            /* !!! This removes lock files as well.  Need to check
-               whether that's okay. */
-            printMsg(lvlError, format("removing referrers file for invalid `%1%'") % from);
-            Path p = referrersFileFor(from);
-            if (unlink(p.c_str()) == -1)
-                throw SysError(format("unlinking `%1%'") % p);
-            continue;
-        }
+        return;
+    }
+    
+    validPaths.insert(path);
+}
 
-        PathSet referrers;
-        bool allValid = queryReferrersInternal(from, referrers);
-        bool update = false;
 
-        if (!allValid) {
-            printMsg(lvlError, format("removing some stale referrers for `%1%'") % from);
-            update = true;
-        }
+/* Functions for upgrading from the pre-SQLite database. */
+
+PathSet LocalStore::queryValidPathsOld()
+{
+    PathSet paths;
+    Strings entries = readDirectory(nixDBPath + "/info");
+    foreach (Strings::iterator, i, entries)
+        if (i->at(0) != '.') paths.insert(nixStore + "/" + *i);
+    return paths;
+}
 
-        /* Each referrer should have a matching reference. */
-        PathSet referrersNew;
-        foreach (PathSet::iterator, j, referrers) {
-            if (referencesCache.find(*j) == referencesCache.end())
-                queryReferences(*j, referencesCache[*j]);
-            if (referencesCache[*j].find(from) == referencesCache[*j].end()) {
-                printMsg(lvlError, format("removing unexpected referrer mapping from `%1%' to `%2%'")
-                    % from % *j);
-                update = true;
-            } else referrersNew.insert(*j);
-        }
 
-        if (update) rewriteReferrers(from, false, referrersNew);
+ValidPathInfo LocalStore::queryPathInfoOld(const Path & path)
+{
+    ValidPathInfo res;
+    res.path = path;
+
+    /* Read the info file. */
+    string baseName = baseNameOf(path);
+    Path infoFile = (format("%1%/info/%2%") % nixDBPath % baseName).str();
+    if (!pathExists(infoFile))
+        throw Error(format("path `%1%' is not valid") % path);
+    string info = readFile(infoFile);
+
+    /* Parse it. */
+    Strings lines = tokenizeString(info, "\n");
+
+    foreach (Strings::iterator, i, lines) {
+        string::size_type p = i->find(':');
+        if (p == string::npos)
+            throw Error(format("corrupt line in `%1%': %2%") % infoFile % *i);
+        string name(*i, 0, p);
+        string value(*i, p + 2);
+        if (name == "References") {
+            Strings refs = tokenizeString(value, " ");
+            res.references = PathSet(refs.begin(), refs.end());
+        } else if (name == "Deriver") {
+            res.deriver = value;
+        } else if (name == "Hash") {
+            res.hash = parseHashField(path, value);
+        } else if (name == "Registered-At") {
+            int n = 0;
+            string2Int(value, n);
+            res.registrationTime = n;
+        }
     }
+
+    return res;
 }
 
 
-/* Upgrade from schema 4 (Nix 0.11) to schema 5 (Nix >= 0.12).  The
-   old schema uses Berkeley DB, the new one stores store path
-   meta-information in files. */
-void LocalStore::upgradeStore12()
+/* Upgrade from schema 5 (Nix 0.12) to schema 6 (Nix >= 0.15). */
+void LocalStore::upgradeStore6()
 {
-    throw Error(
-        "Your Nix store has a database in Berkeley DB format,\n"
-        "which is no longer supported. To convert to the new format,\n"
-        "please upgrade Nix to version 0.12 first.");
+    printMsg(lvlError, "upgrading Nix store to new schema (this may take a while)...");
+
+    openDB(true);
+
+    PathSet validPaths = queryValidPathsOld();
+
+    SQLiteTxn txn(db);
+    
+    foreach (PathSet::iterator, i, validPaths) {
+        addValidPath(queryPathInfoOld(*i));
+        std::cerr << ".";
+    }
+
+    std::cerr << "|";
+    
+    foreach (PathSet::iterator, i, validPaths) {
+        ValidPathInfo info = queryPathInfoOld(*i);
+        unsigned long long referrer = queryValidPathId(*i);
+        foreach (PathSet::iterator, j, info.references)
+            addReference(referrer, queryValidPathId(*j));
+        std::cerr << ".";
+    }
+
+    std::cerr << "\n";
+
+    txn.commit();
 }
 
 
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 31f8d91096a3..0d7ec1f4955b 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -5,6 +5,11 @@
 
 #include "store-api.hh"
 #include "util.hh"
+#include "pathlocks.hh"
+
+
+class sqlite3;
+class sqlite3_stmt;
 
 
 namespace nix {
@@ -12,8 +17,9 @@ namespace nix {
 
 /* Nix store and database schema version.  Version 1 (or 0) was Nix <=
    0.7.  Version 2 was Nix 0.8 and 0.9.  Version 3 is Nix 0.10.
-   Version 4 is Nix 0.11.  Version 5 is Nix 0.12*/
-const int nixSchemaVersion = 5;
+   Version 4 is Nix 0.11.  Version 5 is Nix 0.12-0.16.  Version 6 is
+   Nix 1.0. */
+const int nixSchemaVersion = 6;
 
 
 extern string drvsLogDir;
@@ -41,6 +47,33 @@ struct RunningSubstituter
 };
 
 
+/* Wrapper object to close the SQLite database automatically. */
+struct SQLite
+{
+    sqlite3 * db;
+    SQLite() { db = 0; }
+    ~SQLite();
+    operator sqlite3 * () { return db; }
+};
+
+
+/* Wrapper object to create and destroy SQLite prepared statements. */
+struct SQLiteStmt
+{
+    sqlite3 * db;
+    sqlite3_stmt * stmt;
+    unsigned int curArg;
+    SQLiteStmt() { stmt = 0; }
+    void create(sqlite3 * db, const string & s);
+    void reset();
+    ~SQLiteStmt();
+    operator sqlite3_stmt * () { return stmt; }
+    void bind(const string & value);
+    void bind(int value);
+    void bind();
+};
+    
+
 class LocalStore : public StoreAPI
 {
 private:
@@ -71,6 +104,14 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path queryDeriver(const Path & path);
+
+    /* Return all currently valid derivations that have `path' as an
+       output.  (Note that the result of `queryDeriver()' is the
+       derivation that was actually used to produce `path', which may
+       not exist anymore.) */
+    PathSet queryValidDerivers(const Path & path);
+
+    PathSet queryDerivationOutputs(const Path & path);
     
     PathSet querySubstitutablePaths();
     
@@ -144,6 +185,10 @@ public:
     /* Query whether `path' previously failed to build. */
     bool hasPathFailed(const Path & path);
 
+    PathSet queryFailedPaths();
+
+    void clearFailedPaths(const PathSet & paths);
+
 private:
 
     Path schemaPath;
@@ -151,45 +196,64 @@ private:
     /* Lock file used for upgrading. */
     AutoCloseFD globalLock;
 
-    /* !!! The cache can grow very big.  Maybe it should be pruned
-       every once in a while. */
-    std::map<Path, ValidPathInfo> pathInfoCache;
+    /* The SQLite database object. */
+    SQLite db;
+
+    /* Some precompiled SQLite statements. */
+    SQLiteStmt stmtRegisterValidPath;
+    SQLiteStmt stmtAddReference;
+    SQLiteStmt stmtQueryPathInfo;
+    SQLiteStmt stmtQueryReferences;
+    SQLiteStmt stmtQueryReferrers;
+    SQLiteStmt stmtInvalidatePath;
+    SQLiteStmt stmtRegisterFailedPath;
+    SQLiteStmt stmtHasPathFailed;
+    SQLiteStmt stmtQueryFailedPaths;
+    SQLiteStmt stmtClearFailedPath;
+    SQLiteStmt stmtAddDerivationOutput;
+    SQLiteStmt stmtQueryValidDerivers;
+    SQLiteStmt stmtQueryDerivationOutputs;
 
-    /* Store paths for which the referrers file must be purged. */
-    PathSet delayedUpdates;
+    int getSchema();
 
-    /* Whether to do an fsync() after writing Nix metadata. */
-    bool doFsync;
+    void openDB(bool create);
 
-    int getSchema();
+    unsigned long long queryValidPathId(const Path & path);
 
-    void registerValidPath(const ValidPathInfo & info, bool ignoreValidity = false);
+    unsigned long long addValidPath(const ValidPathInfo & info);
+        
+    void addReference(unsigned long long referrer, unsigned long long reference);
+    
+    void registerValidPath(const ValidPathInfo & info);
 
-    ValidPathInfo queryPathInfo(const Path & path, bool ignoreErrors = false);
+    ValidPathInfo queryPathInfo(const Path & path);
 
     void appendReferrer(const Path & from, const Path & to, bool lock);
     
     void rewriteReferrers(const Path & path, bool purge, PathSet referrers);
 
-    void flushDelayedUpdates();
-    
-    bool queryReferrersInternal(const Path & path, PathSet & referrers);
-    
     void invalidatePath(const Path & path);
-    
-    void upgradeStore12();
+
+    void verifyPath(const Path & path, const PathSet & store,
+        PathSet & done, PathSet & validPaths);
+
+    void upgradeStore6();
+    PathSet queryValidPathsOld();
+    ValidPathInfo queryPathInfoOld(const Path & path);
 
     struct GCState;
 
     bool tryToDelete(GCState & state, const Path & path);
     
-    PathSet findDerivers(GCState & state, const Path & path);
-    
     bool isActiveTempFile(const GCState & state,
         const Path & path, const string & suffix);
         
+    int openGCLock(LockType lockType);
+    
     void startSubstituter(const Path & substituter,
         RunningSubstituter & runningSubstituter);
+
+    Path createTempDirInStore();
 };
 
 
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index f2cc20626915..d52dd6346c7a 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -27,10 +27,10 @@ void computeFSClosure(const Path & storePath,
         store->queryReferences(storePath, references);
 
     if (includeOutputs && isDerivation(storePath)) {
-        Derivation drv = derivationFromPath(storePath);
-        foreach (DerivationOutputs::iterator, i, drv.outputs)
-            if (store->isValidPath(i->second.path))
-                computeFSClosure(i->second.path, paths, flipDirection, true);
+        PathSet outputs = store->queryDerivationOutputs(storePath);
+        foreach (PathSet::iterator, i, outputs)
+            if (store->isValidPath(*i))
+                computeFSClosure(*i, paths, flipDirection, true);
     }
 
     foreach (PathSet::iterator, i, references)
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 3d8b2a0c4263..92d517bbb06f 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -97,10 +97,6 @@ void RemoteStore::forkSlave()
     if (worker == "")
         worker = nixBinDir + "/nix-worker";
 
-    string verbosityArg = "-";
-    for (int i = 1; i < verbosity; ++i)
-        verbosityArg += "v";
-
     child = fork();
     
     switch (child) {
@@ -120,10 +116,7 @@ void RemoteStore::forkSlave()
             close(fdSocket);
             close(fdChild);
 
-            execlp(worker.c_str(), worker.c_str(), "--slave",
-                /* hacky - must be at the end */
-                verbosityArg == "-" ? NULL : verbosityArg.c_str(),
-                NULL);
+            execlp(worker.c_str(), worker.c_str(), "--slave", NULL);
 
             throw SysError(format("executing `%1%'") % worker);
             
@@ -219,7 +212,9 @@ bool RemoteStore::isValidPath(const Path & path)
 PathSet RemoteStore::queryValidPaths()
 {
     openConnection();
-    throw Error("not implemented");
+    writeInt(wopQueryValidPaths, to);
+    processStderr();
+    return readStorePaths(from);
 }
 
 
@@ -299,6 +294,16 @@ Path RemoteStore::queryDeriver(const Path & path)
 }
 
 
+PathSet RemoteStore::queryDerivationOutputs(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryDerivationOutputs, to);
+    writeString(path, to);
+    processStderr();
+    return readStorePaths(from);
+}
+
+
 Path RemoteStore::addToStore(const Path & _srcPath,
     bool recursive, HashType hashAlgo, PathFilter & filter)
 {
@@ -444,6 +449,25 @@ void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
 }
 
 
+PathSet RemoteStore::queryFailedPaths()
+{
+    openConnection();
+    writeInt(wopQueryFailedPaths, to);
+    processStderr();
+    return readStorePaths(from);
+}
+
+
+void RemoteStore::clearFailedPaths(const PathSet & paths)
+{
+    openConnection();
+    writeInt(wopClearFailedPaths, to);
+    writeStringSet(paths, to);
+    processStderr();
+    readInt(from);
+}
+
+
 void RemoteStore::processStderr(Sink * sink, Source * source)
 {
     unsigned int msg;
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 3d55d23d958e..02a1c475252d 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -37,6 +37,8 @@ public:
 
     Path queryDeriver(const Path & path);
     
+    PathSet queryDerivationOutputs(const Path & path);
+    
     bool hasSubstitutes(const Path & path);
     
     bool querySubstitutablePathInfo(const Path & path,
@@ -68,6 +70,10 @@ public:
 
     void collectGarbage(const GCOptions & options, GCResults & results);
     
+    PathSet queryFailedPaths();
+
+    void clearFailedPaths(const PathSet & paths);
+    
 private:
     AutoCloseFD fdSocket;
     FdSink to;
diff --git a/src/libstore/schema.sql b/src/libstore/schema.sql
new file mode 100644
index 000000000000..7438632edbd9
--- /dev/null
+++ b/src/libstore/schema.sql
@@ -0,0 +1,43 @@
+create table if not exists ValidPaths (
+    id               integer primary key autoincrement not null,
+    path             text unique not null,
+    hash             text not null,
+    registrationTime integer not null,
+    deriver          text
+);
+
+create table if not exists Refs (
+    referrer  integer not null,
+    reference integer not null,
+    primary key (referrer, reference),
+    foreign key (referrer) references ValidPaths(id) on delete cascade,
+    foreign key (reference) references ValidPaths(id) on delete restrict
+);
+
+create index if not exists IndexReferrer on Refs(referrer);
+create index if not exists IndexReference on Refs(reference);
+
+-- Paths can refer to themselves, causing a tuple (N, N) in the Refs
+-- table.  This causes a deletion of the corresponding row in
+-- ValidPaths to cause a foreign key constraint violation (due to `on
+-- delete restrict' on the `reference' column).  Therefore, explicitly
+-- get rid of self-references.
+create trigger if not exists DeleteSelfRefs before delete on ValidPaths
+  begin
+    delete from Refs where referrer = old.id and reference = old.id;
+  end;
+
+create table if not exists DerivationOutputs (
+    drv  integer not null,
+    id   text not null, -- symbolic output id, usually "out"
+    path text not null,
+    primary key (drv, id),
+    foreign key (drv) references ValidPaths(id) on delete cascade
+);
+
+create index if not exists IndexDerivationOutputs on DerivationOutputs(path);
+
+create table if not exists FailedPaths (
+    path text primary key not null,
+    time integer not null
+);
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index f0abe61ad1e1..01dd51621625 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1,7 +1,6 @@
 #include "store-api.hh"
 #include "globals.hh"
 #include "util.hh"
-#include "derivations.hh"
 
 #include <limits.h>
 
@@ -53,18 +52,6 @@ Path toStorePath(const Path & path)
 }
 
 
-string getNameOfStorePath(const Path & path)
-{
-    Path::size_type slash = path.rfind('/');
-    string p = slash == Path::npos ? path : string(path, slash + 1);
-    Path::size_type dash = p.find('-');
-    assert(dash != Path::npos);
-    string p2 = string(p, dash + 1);
-    if (isDerivation(p2)) p2 = string(p2, 0, p2.size() - 4);
-    return p2;
-}
-
-
 Path followLinksToStore(const Path & _path)
 {
     Path path = absPath(_path);
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 6fc0689ba1af..082a9edc44c1 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -110,33 +110,18 @@ public:
     virtual void queryReferences(const Path & path,
         PathSet & references) = 0;
 
-    /* Like queryReferences, but with self-references filtered out. */
-    PathSet queryReferencesNoSelf(const Path & path)
-    {
-        PathSet res;
-        queryReferences(path, res);
-        res.erase(path);
-        return res;
-    }
-
     /* Queries the set of incoming FS references for a store path.
        The result is not cleared. */
     virtual void queryReferrers(const Path & path,
         PathSet & referrers) = 0;
 
-    /* Like queryReferrers, but with self-references filtered out. */
-    PathSet queryReferrersNoSelf(const Path & path)
-    {
-        PathSet res;
-        queryReferrers(path, res);
-        res.erase(path);
-        return res;
-    }
-
     /* Query the deriver of a store path.  Return the empty string if
        no deriver has been set. */
     virtual Path queryDeriver(const Path & path) = 0;
 
+    /* Query the outputs of the derivation denoted by `path'. */
+    virtual PathSet queryDerivationOutputs(const Path & path) = 0;
+    
     /* Query whether a path has substitutes. */
     virtual bool hasSubstitutes(const Path & path) = 0;
 
@@ -222,6 +207,13 @@ public:
 
     /* Perform a garbage collection. */
     virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
+
+    /* Return the set of paths that have failed to build.*/
+    virtual PathSet queryFailedPaths() = 0;
+
+    /* Clear the "failed" status of the given paths.  The special
+       value `*' causes all failed paths to be cleared. */
+    virtual void clearFailedPaths(const PathSet & paths) = 0;
 };
 
 
@@ -241,12 +233,6 @@ void checkStoreName(const string & name);
 Path toStorePath(const Path & path);
 
 
-/* Get the "name" part of a store path, that is, the part after the
-   hash and the dash, and with any ".drv" suffix removed
-   (e.g. /nix/store/<hash>-foo-1.2.3.drv => foo-1.2.3). */
-string getNameOfStorePath(const Path & path);
-
-
 /* Follow symlinks until we end up with a path in the Nix store. */
 Path followLinksToStore(const Path & path);
 
@@ -331,6 +317,7 @@ struct ValidPathInfo
     Hash hash;
     PathSet references;
     time_t registrationTime;
+    unsigned long long id; // internal use only
     ValidPathInfo() : registrationTime(0) { }
 };
 
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 5504773b8f91..a4dc690b74d9 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -34,6 +34,10 @@ typedef enum {
     wopSetOptions = 19,
     wopCollectGarbage = 20,
     wopQuerySubstitutablePathInfo = 21,
+    wopQueryDerivationOutputs = 22,
+    wopQueryValidPaths = 23,
+    wopQueryFailedPaths = 24,
+    wopClearFailedPaths = 25,
 } WorkerOp;