Implement RemoteStore::queryMissing()

This provides a significant speedup, e.g. 64 s -> 12 s for

  nix-build --dry-run -I nixpkgs=channel:nixos-16.03 '<nixpkgs/nixos/tests/misc.nix>' -A test

on a cold local and CloudFront cache.

The alternative is to use lots of concurrent daemon connections but
that seems wasteful.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index b6a46642c7c1..8786e2561b9c 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -592,6 +592,17 @@ static void performOp(ref<LocalStore> store, bool trusted, unsigned int clientVe
         break;
     }
 
+    case wopQueryMissing: {
+        PathSet targets = readStorePaths<PathSet>(*store, from);
+        startWork();
+        PathSet willBuild, willSubstitute, unknown;
+        unsigned long long downloadSize, narSize;
+        store->queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize, narSize);
+        stopWork();
+        to << willBuild << willSubstitute << unknown << downloadSize << narSize;
+        break;
+    }
+
     default:
         throw Error(format("invalid operation %1%") % op);
     }