Fix PANIC with track_functions due to concurrent drop of pgstats entries pgstat_drop_entry_internal() generates an ERROR if facing a pgstats entry already marked as dropped. With a workload doing a lot of concurrent CALL and DROP/CREATE PROCEDURE, it could be possible for AtEOXact_PgStat_DroppedStats(), that wants to do transactional drops, to find entries that are already dropped, after a commit record has been written. In this case, ERRORs are upgraded to PANIC, taking down the server.
This issue is fixed by making pgstat_drop_entry() optionally more tolerant to concurrent drops, adding to the routine a missing_ok option to make some of its callers more tolerant (spoiler: some of the callers want a strict behavior, like replication slots and backend stats). pgstat_drop_entry_internal() cannot be called anymore for an entry marked as dropped, hence its error is replaced by an assertion. Functions are handled as a special case in core; this problem could also apply to custom stats kinds depending on what an extension does. track_functions is costly when enabled (disabled by default), which is perhaps the main reason why this has not be found yet. A similar version of this patch has been proposed by Sami Imseih on a different thread for a feature in development. This version has tweaked here by me for the sake of fixing this issue. Reported-by: zhanglihui <[email protected]> Author: Sami Imseih <[email protected]> Author: Michael Paquier <[email protected]> Reviewed-by: Ayush Tiwari <[email protected]> Discussion: https://postgr.es/m/[email protected] Backpatch-through: 15 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/850b9218c8e4aa7a56f4ec34a542d4a37f9e07eb Modified Files -------------- src/backend/utils/activity/pgstat.c | 2 +- src/backend/utils/activity/pgstat_function.c | 2 +- src/backend/utils/activity/pgstat_replslot.c | 2 +- src/backend/utils/activity/pgstat_shmem.c | 28 +++++++++++++++------- src/backend/utils/activity/pgstat_xact.c | 8 +++---- src/include/utils/pgstat_internal.h | 3 ++- .../test_custom_stats/test_custom_var_stats.c | 2 +- 7 files changed, 29 insertions(+), 18 deletions(-)
