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Be more tense about not creating tuplestores with randomAccess = true unless

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backwards scan could actually happen.  In particular, pass a flag to
materialize-mode SRFs that tells them whether they need to require random
access.  In passing, also suppress unneeded backward-scan overhead for a
Portal's holdStore tuplestore.  Per my proposal about reducing I/O costs for
tuplestores.
This commit is contained in:
Tom Lane
2008-10-29 00:00:39 +00:00
parent e3e3d2a789
commit 05bba3d176
11 changed files with 67 additions and 31 deletions
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18
src/backend/utils/mmgr/portalmem.c
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@@ -12,7 +12,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.111 2008/07/18 20:26:06 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/mmgr/portalmem.c,v 1.112 2008/10/29 00:00:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -354,11 +354,17 @@ PortalCreateHoldStore(Portal portal)
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
/* Create the tuple store, selecting cross-transaction temp files. */
/*
* Create the tuple store, selecting cross-transaction temp files, and
* enabling random access only if cursor requires scrolling.
*
* XXX: Should maintenance_work_mem be used for the portal size?
*/
oldcxt = MemoryContextSwitchTo(portal->holdContext);
/* XXX: Should maintenance_work_mem be used for the portal size? */
portal->holdStore = tuplestore_begin_heap(true, true, work_mem);
portal->holdStore =
tuplestore_begin_heap(portal->cursorOptions & CURSOR_OPT_SCROLL,
true, work_mem);
MemoryContextSwitchTo(oldcxt);
}
@@ -913,7 +919,9 @@ pg_cursor(PG_FUNCTION_ARGS)
* We put all the tuples into a tuplestore in one scan of the hashtable.
* This avoids any issue of the hashtable possibly changing between calls.
*/
tupstore = tuplestore_begin_heap(true, false, work_mem);
tupstore =
tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
false, work_mem);
hash_seq_init(&hash_seq, PortalHashTable);
while ((hentry = hash_seq_search(&hash_seq)) != NULL)