Hello,
Sorry, this was no relation with this patch.
ForeignNext materializes the slot, which would be any of physical
and virtual tuple, when system column was requested. If it was a
virtual one, file_fdw makes this, heap_form_tuple generates the
tuple as DatumTuple. The result is a jumble of virtual and
physical. But the returning slot has tts_tuple so the caller
interprets it as a physical one.
Anyway the requests for xmin/xmax could not be prevented
beforehand in current framework, I did rewrite the physical tuple
header so as to really be a physical one.
This would be another patch, so I will put this into next CF if
this don't get any immediate objection.
> By the way, I tried xmin and xmax for the file_fdw tables.
>
> postgres=# select tableoid, xmin, xmax, * from passwd1;
> tableoid | xmin | xmax | uname | pass | uid | gid | ..
> 16396 | 244 | 4294967295 | root | x | 0 | 0 | root...
> 16396 | 252 | 4294967295 | bin | x | 1 | 1 | bin...
> 16396 | 284 | 4294967295 | daemon | x | 2 | 2 |
> daemon...
>
> The xmin and xmax apparently doesn't look sane. After some
> investigation, I found that they came from the following place in
> heap_form_tuple(), (call stach is show below)
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/executor/nodeForeignscan.c b/src/backend/executor/nodeForeignscan.c
index 9cc5345..728db14 100644
--- a/src/backend/executor/nodeForeignscan.c
+++ b/src/backend/executor/nodeForeignscan.c
@@ -22,6 +22,8 @@
*/
#include "postgres.h"
+#include "access/transam.h"
+#include "access/htup_details.h"
#include "executor/executor.h"
#include "executor/nodeForeignscan.h"
#include "foreign/fdwapi.h"
@@ -58,8 +60,21 @@ ForeignNext(ForeignScanState *node)
*/
if (plan->fsSystemCol && !TupIsNull(slot))
{
+ bool was_virtual_tuple = (slot->tts_tuple == NULL);
HeapTuple tup = ExecMaterializeSlot(slot);
+ if (was_virtual_tuple)
+ {
+ /*
+ * ExecMaterializeSlot fills the tuple header as a
+ * DatumTupleFields if the slot was a virtual tuple, but a
+ * physical one is needed here. So rewrite the tuple header as
+ * HeapTupleFirelds.
+ */
+ HeapTupleHeaderSetXmin(tup->t_data, FrozenTransactionId);
+ HeapTupleHeaderSetXmax(tup->t_data, InvalidTransactionId);
+ HeapTupleHeaderSetCmin(tup->t_data, FirstCommandId);
+ }
tup->t_tableOid = RelationGetRelid(node->ss.ss_currentRelation);
}
--
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