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, 79 insertions, 0 deletions

diff --git a/src/backend/executor/execTuples.c b/src/backend/executor/execTuples.c
index a7aa2ee02b1..7a7c7860416 100644
--- a/src/backend/executor/execTuples.c
+++ b/src/backend/executor/execTuples.c
@@ -60,6 +60,7 @@
 #include "access/heaptoast.h"
 #include "access/htup_details.h"
 #include "access/tupdesc_details.h"
+#include "access/xact.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "nodes/nodeFuncs.h"
@@ -149,6 +150,22 @@ tts_virtual_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 }
 
 /*
+ * VirtualTupleTableSlots never have storage tuples.  We generally
+ * shouldn't get here, but provide a user-friendly message if we do.
+ */
+static bool
+tts_virtual_is_current_xact_tuple(TupleTableSlot *slot)
+{
+	Assert(!TTS_EMPTY(slot));
+
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("don't have a storage tuple in this context")));
+
+	return false;				/* silence compiler warnings */
+}
+
+/*
  * To materialize a virtual slot all the datums that aren't passed by value
  * have to be copied into the slot's memory context.  To do so, compute the
  * required size, and allocate enough memory to store all attributes.  That's
@@ -354,6 +371,29 @@ tts_heap_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 						   slot->tts_tupleDescriptor, isnull);
 }
 
+static bool
+tts_heap_is_current_xact_tuple(TupleTableSlot *slot)
+{
+	HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;
+	TransactionId xmin;
+
+	Assert(!TTS_EMPTY(slot));
+
+	/*
+	 * In some code paths it's possible to get here with a non-materialized
+	 * slot, in which case we can't check if tuple is created by the current
+	 * transaction.
+	 */
+	if (!hslot->tuple)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("don't have a storage tuple in this context")));
+
+	xmin = HeapTupleHeaderGetRawXmin(hslot->tuple->t_data);
+
+	return TransactionIdIsCurrentTransactionId(xmin);
+}
+
 static void
 tts_heap_materialize(TupleTableSlot *slot)
 {
@@ -521,6 +561,18 @@ tts_minimal_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 	return 0;					/* silence compiler warnings */
 }
 
+static bool
+tts_minimal_is_current_xact_tuple(TupleTableSlot *slot)
+{
+	Assert(!TTS_EMPTY(slot));
+
+	ereport(ERROR,
+			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			 errmsg("don't have a storage tuple in this context")));
+
+	return false;				/* silence compiler warnings */
+}
+
 static void
 tts_minimal_materialize(TupleTableSlot *slot)
 {
@@ -714,6 +766,29 @@ tts_buffer_heap_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 						   slot->tts_tupleDescriptor, isnull);
 }
 
+static bool
+tts_buffer_is_current_xact_tuple(TupleTableSlot *slot)
+{
+	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
+	TransactionId xmin;
+
+	Assert(!TTS_EMPTY(slot));
+
+	/*
+	 * In some code paths it's possible to get here with a non-materialized
+	 * slot, in which case we can't check if tuple is created by the current
+	 * transaction.
+	 */
+	if (!bslot->base.tuple)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("don't have a storage tuple in this context")));
+
+	xmin = HeapTupleHeaderGetRawXmin(bslot->base.tuple->t_data);
+
+	return TransactionIdIsCurrentTransactionId(xmin);
+}
+
 static void
 tts_buffer_heap_materialize(TupleTableSlot *slot)
 {
@@ -1029,6 +1104,7 @@ const TupleTableSlotOps TTSOpsVirtual = {
 	.getsomeattrs = tts_virtual_getsomeattrs,
 	.getsysattr = tts_virtual_getsysattr,
 	.materialize = tts_virtual_materialize,
+	.is_current_xact_tuple = tts_virtual_is_current_xact_tuple,
 	.copyslot = tts_virtual_copyslot,
 
 	/*
@@ -1048,6 +1124,7 @@ const TupleTableSlotOps TTSOpsHeapTuple = {
 	.clear = tts_heap_clear,
 	.getsomeattrs = tts_heap_getsomeattrs,
 	.getsysattr = tts_heap_getsysattr,
+	.is_current_xact_tuple = tts_heap_is_current_xact_tuple,
 	.materialize = tts_heap_materialize,
 	.copyslot = tts_heap_copyslot,
 	.get_heap_tuple = tts_heap_get_heap_tuple,
@@ -1065,6 +1142,7 @@ const TupleTableSlotOps TTSOpsMinimalTuple = {
 	.clear = tts_minimal_clear,
 	.getsomeattrs = tts_minimal_getsomeattrs,
 	.getsysattr = tts_minimal_getsysattr,
+	.is_current_xact_tuple = tts_minimal_is_current_xact_tuple,
 	.materialize = tts_minimal_materialize,
 	.copyslot = tts_minimal_copyslot,
 
@@ -1082,6 +1160,7 @@ const TupleTableSlotOps TTSOpsBufferHeapTuple = {
 	.clear = tts_buffer_heap_clear,
 	.getsomeattrs = tts_buffer_heap_getsomeattrs,
 	.getsysattr = tts_buffer_heap_getsysattr,
+	.is_current_xact_tuple = tts_buffer_is_current_xact_tuple,
 	.materialize = tts_buffer_heap_materialize,
 	.copyslot = tts_buffer_heap_copyslot,
 	.get_heap_tuple = tts_buffer_heap_get_heap_tuple,