Thread: pgsql: Allow locking updated tuples in tuple_update() and tuple_delete(
pgsql: Allow locking updated tuples in tuple_update() and tuple_delete(
From
Alexander Korotkov
Date:
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 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 patch eliminates step 2 by taking the lock during first tuple_update()/tuple_delete() call. Heap table access method saves some efforts 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. 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/11470f544e3729c60fab890145b2e839cbc8905e Modified Files -------------- src/backend/access/heap/heapam_handler.c | 109 +++++++++++- src/backend/access/table/tableam.c | 6 +- src/backend/executor/nodeModifyTable.c | 288 +++++++++++++------------------ src/include/access/tableam.h | 28 ++- src/include/executor/tuptable.h | 38 ++++ src/tools/pgindent/typedefs.list | 2 + 6 files changed, 285 insertions(+), 186 deletions(-)