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Redesign query-snapshot timing so that volatile functions in READ COMMITTED

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mode see a fresh snapshot for each command in the function, rather than
using the latest interactive command's snapshot.  Also, suppress fresh
snapshots as well as CommandCounterIncrement inside STABLE and IMMUTABLE
functions, instead using the snapshot taken for the most closely nested
regular query.  (This behavior is only sane for read-only functions, so
the patch also enforces that such functions contain only SELECT commands.)
As per my proposal of 6-Sep-2004; I note that I floated essentially the
same proposal on 19-Jun-2002, but that discussion tailed off without any
action.  Since 8.0 seems like the right place to be taking possibly
nontrivial backwards compatibility hits, let's get it done now.
This commit is contained in:
Tom Lane
2004-09-13 20:10:13 +00:00
parent d69528881a
commit b2c4071299
41 changed files with 1764 additions and 834 deletions
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12
src/backend/access/transam/xact.c
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@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.187 2004/09/10 18:39:55 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.188 2004/09/13 20:06:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -401,11 +401,11 @@ CommandCounterIncrement(void)
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("cannot have more than 2^32-1 commands in a transaction")));
/* Propagate new command ID into query snapshots, if set */
if (QuerySnapshot)
QuerySnapshot->curcid = s->commandId;
/* Propagate new command ID into static snapshots, if set */
if (SerializableSnapshot)
SerializableSnapshot->curcid = s->commandId;
if (LatestSnapshot)
LatestSnapshot->curcid = s->commandId;
/*
* make cache changes visible to me.
@ -3001,8 +3001,10 @@ CommitSubTransaction(void)
s->state = TRANS_COMMIT;
/* Mark subtransaction as subcommitted */
/* Must CCI to ensure commands of subtransaction are seen as done */
CommandCounterIncrement();
/* Mark subtransaction as subcommitted */
RecordSubTransactionCommit();
AtSubCommit_childXids();