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Allow locking updated tuples in tuple_update() and tuple_delete()

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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
This commit is contained in:
Alexander Korotkov
2024-03-26 01:27:56 +02:00
parent c7076ba6ad
commit 87985cc925
9 changed files with 502 additions and 346 deletions
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26
src/backend/access/table/tableam.c
View File

@@ -287,16 +287,23 @@ simple_table_tuple_insert(Relation rel, TupleTableSlot *slot)
* via ereport().
*/
void
simple_table_tuple_delete(Relation rel, ItemPointer tid, Snapshot snapshot)
simple_table_tuple_delete(Relation rel, ItemPointer tid, Snapshot snapshot,
TupleTableSlot *oldSlot)
{
TM_Result result;
TM_FailureData tmfd;
int options = TABLE_MODIFY_WAIT; /* wait for commit */
/* Fetch old tuple if the relevant slot is provided */
if (oldSlot)
options |= TABLE_MODIFY_FETCH_OLD_TUPLE;
result = table_tuple_delete(rel, tid,
GetCurrentCommandId(true),
snapshot, InvalidSnapshot,
true /* wait for commit */ ,
&tmfd, false /* changingPart */ );
options,
&tmfd, false /* changingPart */ ,
oldSlot);
switch (result)
{
@@ -335,17 +342,24 @@ void
simple_table_tuple_update(Relation rel, ItemPointer otid,
TupleTableSlot *slot,
Snapshot snapshot,
TU_UpdateIndexes *update_indexes)
TU_UpdateIndexes *update_indexes,
TupleTableSlot *oldSlot)
{
TM_Result result;
TM_FailureData tmfd;
LockTupleMode lockmode;
int options = TABLE_MODIFY_WAIT; /* wait for commit */
/* Fetch old tuple if the relevant slot is provided */
if (oldSlot)
options |= TABLE_MODIFY_FETCH_OLD_TUPLE;
result = table_tuple_update(rel, otid, slot,
GetCurrentCommandId(true),
snapshot, InvalidSnapshot,
true /* wait for commit */ ,
&tmfd, &lockmode, update_indexes);
options,
&tmfd, &lockmode, update_indexes,
oldSlot);
switch (result)
{