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

1 files changed, 20 insertions, 6 deletions

diff --git a/src/backend/access/table/tableam.c b/src/backend/access/table/tableam.c
index e57a0b7ea31..8d3675be959 100644
--- a/src/backend/access/table/tableam.c
+++ b/src/backend/access/table/tableam.c
@@ -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)
 	{