Fix checks for aborted updating transaction in multixids As mentioned in the comments in TransactionIdDidAbort() and in heapam_visibility.c, the usual procedure for checking whether a transaction aborted is to first call TransactionIdIsInProgress(), and then !TransactionIdDidCommit(). A couple places didn't get the memo, and used TransactionIdDidAbort() incorrectly.
In DoesMultiXactIdConflict(), the consequence was that if a conflicting transaction was just aborting, and had already marked the transaction as aborted in pg_xact, but had not yet removed itself from ProcArray, the function would return false meaning that it does not conflict, even though it was still considered as running by TransactionIdIsInProgress(). That could cause trouble later. One known consequence is that if you then went ahead with updating the row again and called MultiXactIdExpand(), MultiXactIdExpand() would see both the old aborting transaction and the new updater as still running, and throw an ERROR: new multixact has more than one updating member. The multixact-aborted-updater.spec included in this commit exercises that scenario. Another place that got this wrong was in heap_update(), where we check if the updating transaction that was part of a multixid committed or aborted. Because it used TransactionIdDidAbort(), if the updating transaction crashed, it was considered as committed and heap_update() incorrectly returned TM_Updated indicating a conflict, even though the row could be updated. This would only happen if the multixid as whole was still considered running, i.e. if the tuple was still locked by other transactions while the updating transaction crashed. That can happen if the locker is a prepared transaction. The included 060_multixact_crashed_updater.pl test tests that scenario. Author: Chee Wooson <[email protected]> Tested-by: Lionel Hamayon <[email protected]> Discussion: https://www.postgresql.org/message-id/[email protected] Backpatch-through: 14 Branch ------ REL_14_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/623cdfa6493d11d47a0d2d31acda16f7fbd0af54 Modified Files -------------- src/backend/access/heap/heapam.c | 30 ++++++--- .../recovery/t/060_multixact_crashed_updater.pl | 75 ++++++++++++++++++++++ 2 files changed, 96 insertions(+), 9 deletions(-)
