Add TupleTableSlotOps.is_current_xact_tuple() method

This allows us to abstract how/whether table AM uses transaction identifiers.
A custom table AM can use a custom slot, which may not store xmin directly,
but determine the tuple belonging to the current transaction in the other way.

Discussion: https://postgr.es/m/CAPpHfdurb9ycV8udYqM%3Do0sPS66PJ4RCBM1g-bBpvzUfogY0EA%40mail.gmail.com
Reviewed-by: Matthias van de Meent, Mark Dilger, Pavel Borisov
Reviewed-by: Nikita Malakhov, Japin Li

1 files changed, 21 insertions, 0 deletions

diff --git a/src/include/executor/tuptable.h b/src/include/executor/tuptable.h
index 6133dbcd0a3..b82655e7e55 100644
--- a/src/include/executor/tuptable.h
+++ b/src/include/executor/tuptable.h
@@ -167,6 +167,12 @@ struct TupleTableSlotOps
 	Datum		(*getsysattr) (TupleTableSlot *slot, int attnum, bool *isnull);
 
 	/*
+	 * Check if the tuple is created by the current transaction. Throws an
+	 * error if the slot doesn't contain the storage tuple.
+	 */
+	bool		(*is_current_xact_tuple) (TupleTableSlot *slot);
+
+	/*
 	 * Make the contents of the slot solely depend on the slot, and not on
 	 * underlying resources (like another memory context, buffers, etc).
 	 */
@@ -427,6 +433,21 @@ slot_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 }
 
 /*
+ * slot_is_current_xact_tuple - check if the slot's current tuple is created
+ *								by the current transaction.
+ *
+ *  If the slot does not contain a storage tuple, this will throw an error.
+ *  Hence before calling this function, callers should make sure that the
+ *  slot type supports storage tuples and that there is currently one inside
+ *  the slot.
+ */
+static inline bool
+slot_is_current_xact_tuple(TupleTableSlot *slot)
+{
+	return slot->tts_ops->is_current_xact_tuple(slot);
+}
+
+/*
  * ExecClearTuple - clear the slot's contents
  */
 static inline TupleTableSlot *