* Only do "pragma journal_mode = ..." if the current journal mode

  differs from the desired mode.  There is an open SQLite ticket
  `Executing "PRAGMA journal_mode" may delete journal file while it is
  in use.'

1 files changed, 10 insertions, 1 deletions

diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index fd6ad6464f..c0c1461b49 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -303,7 +303,16 @@ void LocalStore::openDB(bool create)
        The downside is that it doesn't work over NFS, so allow
        truncate mode alternatively. */
     string mode = queryBoolSetting("use-sqlite-wal", true) ? "wal" : "truncate";
-    if (sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
+    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