* Disable fsync() in SQLite if the fsync-metadata option is set to

false.
* Change the default for `fsync-metadata' to true.
* Disable `fsync-metadata' in `make check'.

doc/manual/conf-file.xml

@@ -241,7 +241,7 @@ build-use-chroot = /dev /proc /bin</programlisting>
     Nix store metadata (in <filename>/nix/var/nix/db</filename>) are
     synchronously flushed to disk.  This improves robustness in case
     of system crashes, but reduces performance.  The default is
-    <literal>false</literal>.</para></listitem>
+    <literal>true</literal>.</para></listitem>
 
   </varlistentry>
     

src/libstore/local-store.cc

@@ -219,9 +219,13 @@ LocalStore::LocalStore()
     /* !!! check whether sqlite has been built with foreign key
        support */
     
-    /* "Normal" synchronous mode should be safe enough. */
-    if (sqlite3_exec(db, "pragma synchronous = normal;", 0, 0, 0) != SQLITE_OK)
-        throw SQLiteError(db, "changing synchronous mode to normal");
+    /* 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");
 
     /* Check the current database schema and if necessary do an
        upgrade.  !!! Race condition: several processes could start
@@ -243,8 +247,6 @@ LocalStore::LocalStore()
             "please upgrade Nix to version 0.12 first.");
     else if (curSchema < 6) upgradeStore6();
     else prepareStatements();
-
-    doFsync = queryBoolSetting("fsync-metadata", false);
 }
 
 

src/libstore/local-store.hh

@@ -191,9 +191,6 @@ private:
     /* Lock file used for upgrading. */
     AutoCloseFD globalLock;
 
-    /* Whether to do an fsync() after writing Nix metadata. */
-    bool doFsync;
-
     /* The SQLite database object. */
     SQLite db;
 

tests/init.sh

@@ -40,6 +40,7 @@ cat > "$NIX_CONF_DIR"/nix.conf <<EOF
 gc-keep-outputs = false
 gc-keep-derivations = false
 env-keep-derivations = false
+fsync-metadata = false
 EOF
 
 mkdir $NIX_DATA_DIR/nix