Allow locking updated tuples in tuple_update() and tuple_delete() Currently, in read committed transaction isolation mode (default), we have the following sequence of actions when tuple_update()/tuple_delete() finds the tuple updated by the concurrent transaction.
1. Attempt to update/delete tuple with tuple_update()/tuple_delete(), which returns TM_Updated. 2. Lock tuple with tuple_lock(). 3. Re-evaluate plan qual (recheck if we still need to update/delete and calculate the new tuple for update). 4. Second attempt to update/delete tuple with tuple_update()/tuple_delete(). This attempt should be successful, since the tuple was previously locked. This commit eliminates step 2 by taking the lock during the first tuple_update()/tuple_delete() call. The heap table access method saves some effort by checking the updated tuple once instead of twice. Future undo-based table access methods, which will start from the latest row version, can immediately place a lock there. Also, this commit makes tuple_update()/tuple_delete() optionally save the old tuple into the dedicated slot. That saves efforts on re-fetching tuples in certain cases. The code in nodeModifyTable.c is simplified by removing the nested switch/case. Discussion: https://postgr.es/m/CAPpHfdua-YFw3XTprfutzGp28xXLigFtzNbuFY8yPhqeq6X5kg%40mail.gmail.com Reviewed-by: Aleksander Alekseev, Pavel Borisov, Vignesh C, Mason Sharp Reviewed-by: Andres Freund, Chris Travers Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/87985cc9252296f11db3cacc155e8d710d2e9b9c Modified Files -------------- src/backend/access/heap/heapam.c | 205 +++++++++++++----- src/backend/access/heap/heapam_handler.c | 94 ++++++-- src/backend/access/table/tableam.c | 26 ++- src/backend/commands/trigger.c | 55 ++--- src/backend/executor/execReplication.c | 19 +- src/backend/executor/nodeModifyTable.c | 353 ++++++++++++++----------------- src/include/access/heapam.h | 19 +- src/include/access/tableam.h | 73 +++++-- src/include/commands/trigger.h | 4 +- 9 files changed, 502 insertions(+), 346 deletions(-)