Fix some more cases of missed GENERATED-column updates.

If UPDATE is forced to retry after an EvalPlanQual check, it neglected
to repeat GENERATED-column computations, even though those might well
have changed since we're dealing with a different tuple than before.
Fixing this is mostly a matter of looping back a bit further when
we retry.  In v15 and HEAD that's most easily done by altering the API
of ExecUpdateAct so that it includes computing GENERATED expressions.

Also, if an UPDATE in a partitioned table turns into a cross-partition
INSERT operation, we failed to recompute GENERATED columns.  That's a
bug since 8bf6ec3ba allowed partitions to have different generation
expressions; although it seems to have no ill effects before that.
Fixing this is messier because we can now have situations where the same
query needs both the UPDATE-aligned set of GENERATED columns and the
INSERT-aligned set, and it's unclear which set will be generated first
(else we could hack things by forcing the INSERT-aligned set to be
generated, which is indeed how fe9e658f4 made it work for MERGE).
The best fix seems to be to build and store separate sets of expressions
for the INSERT and UPDATE cases.  That would create ABI issues in the
back branches, but so far it seems we can leave this alone in the back
branches.

Per bug #17823 from Hisahiro Kauchi.  The first part of this affects all
branches back to v12 where GENERATED columns were added.

Discussion: https://postgr.es/m/17823-b64909cf7d63de84@postgresql.org

1 files changed, 26 insertions, 16 deletions

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index ad0aa8dd9d7..802bea0e6d3 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -358,8 +358,9 @@ ExecCheckTIDVisible(EState *estate,
  *
  * This fills the resultRelInfo's ri_GeneratedExprs field and makes an
  * associated ResultRelInfoExtra struct to hold ri_extraUpdatedCols.
- * (Currently, ri_extraUpdatedCols is consulted only in UPDATE, but we might
- * as well fill it for INSERT too.)
+ * (Currently, ri_extraUpdatedCols is consulted only in UPDATE, but we
+ * must fill it in other cases too, since for example cmdtype might be
+ * MERGE yet an UPDATE might happen later.)
  */
 void
 ExecInitStoredGenerated(ResultRelInfo *resultRelInfo,
@@ -1918,9 +1919,10 @@ ExecUpdatePrologue(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 }
 
 /*
- * ExecUpdatePrepareSlot -- subroutine for ExecUpdate
+ * ExecUpdatePrepareSlot -- subroutine for ExecUpdateAct
  *
  * Apply the final modifications to the tuple slot before the update.
+ * (This is split out because we also need it in the foreign-table code path.)
  */
 static void
 ExecUpdatePrepareSlot(ResultRelInfo *resultRelInfo,
@@ -1973,13 +1975,14 @@ ExecUpdateAct(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 	updateCxt->crossPartUpdate = false;
 
 	/*
-	 * If we generate a new candidate tuple after EvalPlanQual testing, we
-	 * must loop back here and recheck any RLS policies and constraints. (We
-	 * don't need to redo triggers, however.  If there are any BEFORE triggers
-	 * then trigger.c will have done table_tuple_lock to lock the correct
-	 * tuple, so there's no need to do them again.)
+	 * If we move the tuple to a new partition, we loop back here to recompute
+	 * GENERATED values (which are allowed to be different across partitions)
+	 * and recheck any RLS policies and constraints.  We do not fire any
+	 * BEFORE triggers of the new partition, however.
 	 */
-lreplace:;
+lreplace:
+	/* Fill in GENERATEd columns */
+	ExecUpdatePrepareSlot(resultRelInfo, slot, estate);
 
 	/* ensure slot is independent, consider e.g. EPQ */
 	ExecMaterializeSlot(slot);
@@ -2279,6 +2282,7 @@ ExecUpdate(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 	}
 	else if (resultRelInfo->ri_FdwRoutine)
 	{
+		/* Fill in GENERATEd columns */
 		ExecUpdatePrepareSlot(resultRelInfo, slot, estate);
 
 		/*
@@ -2301,9 +2305,13 @@ ExecUpdate(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 	}
 	else
 	{
-		/* Fill in the slot appropriately */
-		ExecUpdatePrepareSlot(resultRelInfo, slot, estate);
-
+		/*
+		 * If we generate a new candidate tuple after EvalPlanQual testing, we
+		 * must loop back here to try again.  (We don't need to redo triggers,
+		 * however.  If there are any BEFORE triggers then trigger.c will have
+		 * done table_tuple_lock to lock the correct tuple, so there's no need
+		 * to do them again.)
+		 */
 redo_act:
 		result = ExecUpdateAct(context, resultRelInfo, tupleid, oldtuple, slot,
 							   canSetTag, &updateCxt);
@@ -2887,7 +2895,6 @@ lmerge_matched:;
 					result = TM_Ok;
 					break;
 				}
-				ExecUpdatePrepareSlot(resultRelInfo, newslot, context->estate);
 				result = ExecUpdateAct(context, resultRelInfo, tupleid, NULL,
 									   newslot, false, &updateCxt);
 				if (result == TM_Ok && updateCxt.updated)
@@ -4149,9 +4156,12 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 
 		/*
 		 * For INSERT/UPDATE/MERGE, prepare to evaluate any generated columns.
-		 * We must do this now, even if we never insert or update any rows,
-		 * because we have to fill resultRelInfo->ri_extraUpdatedCols for
-		 * possible use by the trigger machinery.
+		 * We must do this now, even if we never insert or update any rows, to
+		 * cover the case where a MERGE does some UPDATE operations and later
+		 * some INSERTs.  We'll need ri_GeneratedExprs to cover all generated
+		 * columns, so we force it now.  (It might be sufficient to do this
+		 * only for operation == CMD_MERGE, but we'll avoid changing the data
+		 * structure definition in back branches.)
 		 */
 		if (operation == CMD_INSERT || operation == CMD_UPDATE || operation == CMD_MERGE)
 			ExecInitStoredGenerated(resultRelInfo, estate, operation);