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* Use SQLite 3.7.0's write-ahead logging (WAL mode). This is a lot

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faster than the old mode when fsyncs are enabled, because it only
  performs an fsync() when doing a checkpoint, rather than at every
  commit.  Some timings for doing a "nix-instantiate /etc/nixos/nixos
  -A system" after modifying the stdenv setup script:

    42.5s - SQLite 3.6.23 with truncate mode and fsync
     3.4s - SQLite 3.6.23 with truncate mode and no fsync
    32.1s - SQLite 3.7.0 with truncate mode and fsync
    16.8s - SQLite 3.7.0 with WAL mode and fsync, auto-checkpoint
            every 1000 pages
     8.3s - SQLite 3.7.0 with WAL mode and fsync, auto-checkpoint
            every 8192 pages
     1.7s - SQLite 3.7.0 with WAL mode and no fsync

  The default is now to use WAL mode with fsyncs.  Because WAL doesn't
  work on remote filesystems such as NFS (as it uses shared memory),
  truncate mode can be re-enabled by setting the "use-sqlite-wal"
  option to false.
This commit is contained in:
Eelco Dolstra 2010-08-04 17:35:59 +00:00
parent 7f893b7a43
commit fd9c77dfc7
3 changed files with 14 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

14
src/libstore/local-store.cc
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@ -298,10 +298,20 @@ void LocalStore::openDB(bool create)
if (sqlite3_exec(db, ("pragma synchronous = " + syncMode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
throw SQLiteError(db, "setting synchronous mode");
/* Use `truncate' journal mode, which should be a bit faster. */
if (sqlite3_exec(db, "pragma main.journal_mode = truncate;", 0, 0, 0) != SQLITE_OK)
/* Set the SQLite journal mode. The default is write-ahead
logging since it's the fastest and supports more concurrency.
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)
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"