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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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10
src/backend/commands/vacuum.c
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@@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.290 2004/08/30 02:54:38 momjian Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.291 2004/09/13 20:06:29 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -402,8 +402,8 @@ vacuum(VacuumStmt *vacstmt)
if (use_own_xacts)
{
StartTransactionCommand();
SetQuerySnapshot(); /* might be needed for functions
* in indexes */
/* functions in indexes may want a snapshot set */
ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
}
else
old_context = MemoryContextSwitchTo(anl_context);
@@ -865,8 +865,8 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
/* Begin a transaction for vacuuming this relation */
StartTransactionCommand();
SetQuerySnapshot(); /* might be needed for functions in
* indexes */
/* functions in indexes may want a snapshot set */
ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
/*
* Tell the cache replacement strategy that vacuum is causing all