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Combine cmin and cmax fields of HeapTupleHeaders into a single field, by

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keeping private state in each backend that has inserted and deleted the same
tuple during its current top-level transaction.  This is sufficient since
there is no need to be able to determine the cmin/cmax from any other
transaction.  This gets us back down to 23-byte headers, removing a penalty
paid in 8.0 to support subtransactions.  Patch by Heikki Linnakangas, with
minor revisions by moi, following a design hashed out awhile back on the
pghackers list.
This commit is contained in:
Tom Lane
2007-02-09 03:35:35 +00:00
parent acb3416686
commit c398300330
21 changed files with 799 additions and 127 deletions
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14
src/backend/access/common/heaptuple.c
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@ -16,7 +16,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/common/heaptuple.c,v 1.114 2007/01/09 22:00:59 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/common/heaptuple.c,v 1.115 2007/02/09 03:35:33 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -582,14 +582,18 @@ heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
case MinTransactionIdAttributeNumber:
result = TransactionIdGetDatum(HeapTupleHeaderGetXmin(tup->t_data));
break;
case MinCommandIdAttributeNumber:
result = CommandIdGetDatum(HeapTupleHeaderGetCmin(tup->t_data));
break;
case MaxTransactionIdAttributeNumber:
result = TransactionIdGetDatum(HeapTupleHeaderGetXmax(tup->t_data));
break;
case MinCommandIdAttributeNumber:
case MaxCommandIdAttributeNumber:
result = CommandIdGetDatum(HeapTupleHeaderGetCmax(tup->t_data));
/*
* cmin and cmax are now both aliases for the same field,
* which can in fact also be a combo command id. XXX perhaps we
* should return the "real" cmin or cmax if possible, that is
* if we are inside the originating transaction?
*/
result = CommandIdGetDatum(HeapTupleHeaderGetRawCommandId(tup->t_data));
break;
case TableOidAttributeNumber:
result = ObjectIdGetDatum(tup->t_tableOid);