From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=ALL_TRUSTED,BAYES_00 shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from localhost (dcvr.yhbt.net [127.0.0.1]) by dcvr.yhbt.net (Postfix) with ESMTP id 604421F66E; Tue, 25 Aug 2020 10:23:14 +0000 (UTC) Date: Tue, 25 Aug 2020 10:23:14 +0000 From: Eric Wong To: meta@public-inbox.org Subject: [PATCH] grok-pull.post_update_hook: flock(2) before SQLite check Message-ID: <20200825102314.GA19671@dcvr> References: <20200825001204.GA840@dcvr> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200825001204.GA840@dcvr> List-Id: Unlike DBD::SQLite, the sqlite3(1) CLI does not have a default busy timeout enabled, so it easily times out while acquiring a SHARED lock for read-only queries. We can avoid battery-wasting polling from the SQLite timeout handler by relying on flock(2) as we do in our Perl code. Furthermore, this avoids triggering some locking problems[1] from a long "SELECT COUNT(*) ..." query and reindex. While there may be other SQLite-related parallelism issues[1], this works around one of them by relying on flock(2). [1] https://public-inbox.org/meta/20200825001204.GA840@dcvr/ --- examples/grok-pull.post_update_hook.sh | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/examples/grok-pull.post_update_hook.sh b/examples/grok-pull.post_update_hook.sh index 1f51140f..77489472 100755 --- a/examples/grok-pull.post_update_hook.sh +++ b/examples/grok-pull.post_update_hook.sh @@ -25,11 +25,13 @@ then inbox_dir=$(expr "$full_git_dir" : "$EPOCH2MAIN") inbox_name=$(basename "$inbox_dir") msgmap="$inbox_dir"/msgmap.sqlite3 + inbox_lock="$inbox_dir"/inbox.lock else inbox_fmt=1 inbox_dir="$full_git_dir" inbox_name=$(basename "$inbox_dir" .git) msgmap="$inbox_dir"/public-inbox/msgmap.sqlite3 + inbox_lock="$inbox_dir"/ssoma.lock fi # run public-inbox-init iff unconfigured @@ -118,7 +120,18 @@ esac # don't know what indexlevel a user wants if test -f "$msgmap" then - n=$(echo 'SELECT COUNT(*) FROM msgmap' | sqlite3 -readonly "$msgmap") + # We need to use flock(1) (from util-linux) to avoid timeouts + # and SQLite locking problems. + # FreeBSD has a similar lockf(1) utility, but it unlinks by + # default so we use `-k' to keep the lock on the FS. + FLOCK=flock + case $(uname -s) in + FreeBSD) FLOCK='lockf -k' ;; + # ... other OSes here + esac + + n=$(echo 'SELECT COUNT(*) FROM msgmap' | \ + $FLOCK $inbox_lock sqlite3 -readonly "$msgmap") case $n in 0|'') : v2 inboxes may be init-ed with an empty msgmap