8000 Fix "database is locked" due to concurrent writes between follow and clone. by shubhamdhama · Pull Request #712 · dimitri/pgcopydb · GitHub
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Fix "database is locked" due to concurrent writes between follow and clone. #712

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Merged
merged 1 commit into from
Mar 21, 2024
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Fix "database is locked" due to concurrent writes between follow and clone. #712

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18 changes: 18 additions & 0 deletions src/bin/pgcopydb/cli_clone_follow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -249,6 +249,24 @@ clone_and_follow(CopyDataSpec *copySpecs)
exit(EXIT_CODE_INTERNAL_ERROR);
}

/*
* We fetch the schema here, rather than later in the clone subprocess,
* which simply reuses this cached data. This is done to avoid lock
* contention between the clone and follow subprocesses, as they both try to
* write concurrently to the source.db SQLite database, leading one to
* failure. This is also necessary for plugins like test_decoding, which
* require information such as primary keys.
*
* In the future, if the follow subprocess doesn't need a catalog (e.g. if
* we remove test_decoding), we should separate out tables for the follow
* subprocess into their own database.
*/
if (!copydb_fetch_schema_and_prepare_specs(copySpecs))
{
/* errors have already been logged */
exit(EXIT_CODE_INTERNAL_ERROR);
}

/*
* Preparation and snapshot are now done, time to fork our two main worker
* processes.
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