tableam: Add and use table_fetch_row_version().

This is essentially the tableam version of heapam_fetch(),
i.e. fetching a tuple identified by a tid, performing visibility
checks.

Note that this different from table_index_fetch_tuple(), which is for
index lookups. It therefore has to handle a tid pointing to an earlier
version of a tuple if the AM uses an optimization like heap's HOT. Add
comments to that end.

This commit removes the stats_relation argument from heap_fetch, as
it's been unused for a long time.

Author: Andres Freund
Reviewed-By: Haribabu Kommi
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de

1 files changed, 3 insertions, 19 deletions

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 1374b751767..7be0e7745af 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -229,17 +229,13 @@ ExecCheckTIDVisible(EState *estate,
 					TupleTableSlot *tempSlot)
 {
 	Relation	rel = relinfo->ri_RelationDesc;
-	Buffer		buffer;
-	HeapTupleData tuple;
 
 	/* Redundantly check isolation level */
 	if (!IsolationUsesXactSnapshot())
 		return;
 
-	tuple.t_self = *tid;
-	if (!heap_fetch(rel, SnapshotAny, &tuple, &buffer, NULL))
+	if (!table_fetch_row_version(rel, tid, SnapshotAny, tempSlot))
 		elog(ERROR, "failed to fetch conflicting tuple for ON CONFLICT");
-	ExecStorePinnedBufferHeapTuple(&tuple, tempSlot, buffer);
 	ExecCheckTupleVisible(estate, rel, tempSlot);
 	ExecClearTuple(tempSlot);
 }
@@ -874,21 +870,9 @@ ldelete:;
 			}
 			else
 			{
-				BufferHeapTupleTableSlot *bslot;
-				HeapTuple	deltuple;
-				Buffer		buffer;
-
-				Assert(TTS_IS_BUFFERTUPLE(slot));
-				ExecClearTuple(slot);
-				bslot = (BufferHeapTupleTableSlot *) slot;
-				deltuple = &bslot->base.tupdata;
-
-				deltuple->t_self = *tupleid;
-				if (!heap_fetch(resultRelationDesc, SnapshotAny,
-								deltuple, &buffer, NULL))
+				if (!table_fetch_row_version(resultRelationDesc, tupleid,
+											 SnapshotAny, slot))
 					elog(ERROR, "failed to fetch deleted tuple for DELETE RETURNING");
-
-				ExecStorePinnedBufferHeapTuple(deltuple, slot, buffer);
 			}
 		}