* [PATCH] grok-pull.post_update_hook: flock(2) before SQLite check
@ 2020-08-25 10:23 7% ` Eric Wong
0 siblings, 0 replies; 1+ results
From: Eric Wong @ 2020-08-25 10:23 UTC (permalink / raw)
To: meta
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
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2020-08-25 0:12 anybody hit SQLite "database is locked" errors? Eric Wong
2020-08-25 10:23 7% ` [PATCH] grok-pull.post_update_hook: flock(2) before SQLite check Eric Wong
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