Add a new column to pg_am to specify whether an index AM supports backward
scanning; GiST and GIN do not, and it seems like too much trouble to make them do so. By teaching ExecSupportsBackwardScan() about this restriction, we ensure that the planner will protect a scroll cursor from the problem by adding a Materialize node. In passing, fix another longstanding bug in the same area: backwards scan of a plan with set-returning functions in the targetlist did not work either, since the TupFromTlist expansion code pays no attention to direction (and has no way to run a SRF backwards anyway). Again the fix is to make ExecSupportsBackwardScan check this restriction. Also adjust the index AM API specification to note that mark/restore support is unnecessary if the AM can't produce ordered output.
This commit is contained in:
Tom Lane
parent
2a64931c4b
commit
e4fb8ff06a
|
|
@ -1,4 +1,4 @@
|
|||
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.178 2008/10/06 13:59:37 tgl Exp $ -->
|
||||
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.179 2008/10/17 22:10:29 tgl Exp $ -->
|
||||
<!--
|
||||
Documentation of the system catalogs, directed toward PostgreSQL developers
|
||||
-->
|
||||
|
|
@ -401,6 +401,13 @@
|
|||
<entry>Does the access method support ordered scans?</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry><structfield>amcanbackward</structfield></entry>
|
||||
<entry><type>bool</type></entry>
|
||||
<entry></entry>
|
||||
<entry>Does the access method support backward scanning?</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry><structfield>amcanunique</structfield></entry>
|
||||
<entry><type>bool</type></entry>
|
||||
|
|
|
|||
|
|
@ -1,4 +1,4 @@
|
|||
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.27 2008/08/14 18:47:58 tgl Exp $ -->
|
||||
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.28 2008/10/17 22:10:29 tgl Exp $ -->
|
||||
|
||||
<chapter id="indexam">
|
||||
<title>Index Access Method Interface Definition</title>
|
||||
|
|
@ -474,15 +474,20 @@ amrestrpos (IndexScanDesc scan);
|
|||
normally would. (This will only occur for access
|
||||
methods that advertise they support ordered scans.) After the
|
||||
first call, <function>amgettuple</> must be prepared to advance the scan in
|
||||
either direction from the most recently returned entry.
|
||||
either direction from the most recently returned entry. (But if
|
||||
<structname>pg_am</>.<structfield>amcanbackward</> is false, all subsequent
|
||||
calls will have the same direction as the first one.)
|
||||
</para>
|
||||
|
||||
<para>
|
||||
The access method must support <quote>marking</> a position in a scan
|
||||
and later returning to the marked position. The same position might be
|
||||
restored multiple times. However, only one position need be remembered
|
||||
per scan; a new <function>ammarkpos</> call overrides the previously
|
||||
marked position.
|
||||
Access methods that support ordered scans must support <quote>marking</> a
|
||||
position in a scan and later returning to the marked position. The same
|
||||
position might be restored multiple times. However, only one position need
|
||||
be remembered per scan; a new <function>ammarkpos</> call overrides the
|
||||
previously marked position. An access method that does not support
|
||||
ordered scans should still provide mark and restore functions in
|
||||
<structname>pg_am</>, but it is sufficient to have them throw errors if
|
||||
called.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
|
|
|
|||
|
|
@ -6,7 +6,7 @@
|
|||
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.99 2008/10/04 21:56:53 tgl Exp $
|
||||
* $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.100 2008/10/17 22:10:29 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
|
|
@ -42,6 +42,12 @@
|
|||
#include "executor/nodeValuesscan.h"
|
||||
#include "executor/nodeCtescan.h"
|
||||
#include "executor/nodeWorktablescan.h"
|
||||
#include "nodes/nodeFuncs.h"
|
||||
#include "utils/syscache.h"
|
||||
|
||||
|
||||
static bool TargetListSupportsBackwardScan(List *targetlist);
|
||||
static bool IndexSupportsBackwardScan(Oid indexid);
|
||||
|
||||
|
||||
/*
|
||||
|
|
@ -390,7 +396,8 @@ ExecSupportsBackwardScan(Plan *node)
|
|||
{
|
||||
case T_Result:
|
||||
if (outerPlan(node) != NULL)
|
||||
return ExecSupportsBackwardScan(outerPlan(node));
|
||||
return ExecSupportsBackwardScan(outerPlan(node)) &&
|
||||
TargetListSupportsBackwardScan(node->targetlist);
|
||||
else
|
||||
return false;
|
||||
|
||||
|
|
@ -403,29 +410,85 @@ ExecSupportsBackwardScan(Plan *node)
|
|||
if (!ExecSupportsBackwardScan((Plan *) lfirst(l)))
|
||||
return false;
|
||||
}
|
||||
/* need not check tlist because Append doesn't evaluate it */
|
||||
return true;
|
||||
}
|
||||
|
||||
case T_SeqScan:
|
||||
case T_IndexScan:
|
||||
case T_TidScan:
|
||||
case T_FunctionScan:
|
||||
case T_ValuesScan:
|
||||
case T_CteScan:
|
||||
case T_WorkTableScan:
|
||||
return true;
|
||||
return TargetListSupportsBackwardScan(node->targetlist);
|
||||
|
||||
case T_IndexScan:
|
||||
return IndexSupportsBackwardScan(((IndexScan *) node)->indexid) &&
|
||||
TargetListSupportsBackwardScan(node->targetlist);
|
||||
|
||||
case T_SubqueryScan:
|
||||
return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan);
|
||||
return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan) &&
|
||||
TargetListSupportsBackwardScan(node->targetlist);
|
||||
|
||||
case T_Material:
|
||||
case T_Sort:
|
||||
/* these don't evaluate tlist */
|
||||
return true;
|
||||
|
||||
case T_Limit:
|
||||
/* doesn't evaluate tlist */
|
||||
return ExecSupportsBackwardScan(outerPlan(node));
|
||||
|
||||
default:
|
||||
return false;
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* If the tlist contains set-returning functions, we can't support backward
|
||||
* scan, because the TupFromTlist code is direction-ignorant.
|
||||
*/
|
||||
static bool
|
||||
TargetListSupportsBackwardScan(List *targetlist)
|
||||
{
|
||||
if (expression_returns_set((Node *) targetlist))
|
||||
return false;
|
||||
return true;
|
||||
}
|
||||
|
||||
/*
|
||||
* An IndexScan node supports backward scan only if the index's AM does.
|
||||
*/
|
||||
static bool
|
||||
IndexSupportsBackwardScan(Oid indexid)
|
||||
{
|
||||
bool result;
|
||||
HeapTuple ht_idxrel;
|
||||
HeapTuple ht_am;
|
||||
Form_pg_class idxrelrec;
|
||||
Form_pg_am amrec;
|
||||
|
||||
/* Fetch the pg_class tuple of the index relation */
|
||||
ht_idxrel = SearchSysCache(RELOID,
|
||||
ObjectIdGetDatum(indexid),
|
||||
0, 0, 0);
|
||||
if (!HeapTupleIsValid(ht_idxrel))
|
||||
elog(ERROR, "cache lookup failed for relation %u", indexid);
|
||||
idxrelrec = (Form_pg_class) GETSTRUCT(ht_idxrel);
|
||||
|
||||
/* Fetch the pg_am tuple of the index' access method */
|
||||
ht_am = SearchSysCache(AMOID,
|
||||
ObjectIdGetDatum(idxrelrec->relam),
|
||||
0, 0, 0);
|
||||
if (!HeapTupleIsValid(ht_am))
|
||||
elog(ERROR, "cache lookup failed for access method %u",
|
||||
idxrelrec->relam);
|
||||
amrec = (Form_pg_am) GETSTRUCT(ht_am);
|
||||
|
||||
result = amrec->amcanbackward;
|
||||
|
||||
ReleaseSysCache(ht_idxrel);
|
||||
ReleaseSysCache(ht_am);
|
||||
|
||||
return result;
|
||||
}
|
||||
|
|
|
|||
|
|
@ -37,7 +37,7 @@
|
|||
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.498 2008/10/14 17:12:33 tgl Exp $
|
||||
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.499 2008/10/17 22:10:30 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
|
|
@ -53,6 +53,6 @@
|
|||
*/
|
||||
|
||||
/* yyyymmddN */
|
||||
#define CATALOG_VERSION_NO 200810141
|
||||
#define CATALOG_VERSION_NO 200810171
|
||||
|
||||
#endif
|
||||
|
|
|
|||
|
|
@ -8,7 +8,7 @@
|
|||
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
|
||||
* Portions Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $PostgreSQL: pgsql/src/include/catalog/pg_am.h,v 1.58 2008/09/15 18:43:41 tgl Exp $
|
||||
* $PostgreSQL: pgsql/src/include/catalog/pg_am.h,v 1.59 2008/10/17 22:10:30 tgl Exp $
|
||||
*
|
||||
* NOTES
|
||||
* the genbki.sh script reads this file and generates .bki
|
||||
|
|
@ -41,6 +41,7 @@ CATALOG(pg_am,2601)
|
|||
int2 amsupport; /* total number of support functions that this
|
||||
* AM uses */
|
||||
bool amcanorder; /* does AM support ordered scan results? */
|
||||
bool amcanbackward; /* does AM support backward scan? */
|
||||
bool amcanunique; /* does AM support UNIQUE indexes? */
|
||||
bool amcanmulticol; /* does AM support multi-column indexes? */
|
||||
bool amoptionalkey; /* can query omit key for the first column? */
|
||||
|
|
@ -75,48 +76,49 @@ typedef FormData_pg_am *Form_pg_am;
|
|||
* compiler constants for pg_am
|
||||
* ----------------
|
||||
*/
|
||||
#define Natts_pg_am 25
|
||||
#define Natts_pg_am 26
|
||||
#define Anum_pg_am_amname 1
|
||||
#define Anum_pg_am_amstrategies 2
|
||||
#define Anum_pg_am_amsupport 3
|
||||
#define Anum_pg_am_amcanorder 4
|
||||
#define Anum_pg_am_amcanunique 5
|
||||
#define Anum_pg_am_amcanmulticol 6
|
||||
#define Anum_pg_am_amoptionalkey 7
|
||||
#define Anum_pg_am_amindexnulls 8
|
||||
#define Anum_pg_am_amsearchnulls 9
|
||||
#define Anum_pg_am_amstorage 10
|
||||
#define Anum_pg_am_amclusterable 11
|
||||
#define Anum_pg_am_amkeytype 12
|
||||
#define Anum_pg_am_aminsert 13
|
||||
#define Anum_pg_am_ambeginscan 14
|
||||
#define Anum_pg_am_amgettuple 15
|
||||
#define Anum_pg_am_amgetbitmap 16
|
||||
#define Anum_pg_am_amrescan 17
|
||||
#define Anum_pg_am_amendscan 18
|
||||
#define Anum_pg_am_ammarkpos 19
|
||||
#define Anum_pg_am_amrestrpos 20
|
||||
#define Anum_pg_am_ambuild 21
|
||||
#define Anum_pg_am_ambulkdelete 22
|
||||
#define Anum_pg_am_amvacuumcleanup 23
|
||||
#define Anum_pg_am_amcostestimate 24
|
||||
#define Anum_pg_am_amoptions 25
|
||||
#define Anum_pg_am_amcanbackward 5
|
||||
#define Anum_pg_am_amcanunique 6
|
||||
#define Anum_pg_am_amcanmulticol 7
|
||||
#define Anum_pg_am_amoptionalkey 8
|
||||
#define Anum_pg_am_amindexnulls 9
|
||||
#define Anum_pg_am_amsearchnulls 10
|
||||
#define Anum_pg_am_amstorage 11
|
||||
#define Anum_pg_am_amclusterable 12
|
||||
#define Anum_pg_am_amkeytype 13
|
||||
#define Anum_pg_am_aminsert 14
|
||||
#define Anum_pg_am_ambeginscan 15
|
||||
#define Anum_pg_am_amgettuple 16
|
||||
#define Anum_pg_am_amgetbitmap 17
|
||||
#define Anum_pg_am_amrescan 18
|
||||
#define Anum_pg_am_amendscan 19
|
||||
#define Anum_pg_am_ammarkpos 20
|
||||
#define Anum_pg_am_amrestrpos 21
|
||||
#define Anum_pg_am_ambuild 22
|
||||
#define Anum_pg_am_ambulkdelete 23
|
||||
#define Anum_pg_am_amvacuumcleanup 24
|
||||
#define Anum_pg_am_amcostestimate 25
|
||||
#define Anum_pg_am_amoptions 26
|
||||
|
||||
/* ----------------
|
||||
* initial contents of pg_am
|
||||
* ----------------
|
||||
*/
|
||||
|
||||
DATA(insert OID = 403 ( btree 5 1 t t t t t t f t 0 btinsert btbeginscan btgettuple btgetbitmap btrescan btendscan btmarkpos btrestrpos btbuild btbulkdelete btvacuumcleanup btcostestimate btoptions ));
|
||||
DATA(insert OID = 403 ( btree 5 1 t t t t t t t f t 0 btinsert btbeginscan btgettuple btgetbitmap btrescan btendscan btmarkpos btrestrpos btbuild btbulkdelete btvacuumcleanup btcostestimate btoptions ));
|
||||
DESCR("b-tree index access method");
|
||||
#define BTREE_AM_OID 403
|
||||
DATA(insert OID = 405 ( hash 1 1 f f f f f f f f 23 hashinsert hashbeginscan hashgettuple hashgetbitmap hashrescan hashendscan hashmarkpos hashrestrpos hashbuild hashbulkdelete hashvacuumcleanup hashcostestimate hashoptions ));
|
||||
DATA(insert OID = 405 ( hash 1 1 f t f f f f f f f 23 hashinsert hashbeginscan hashgettuple hashgetbitmap hashrescan hashendscan hashmarkpos hashrestrpos hashbuild hashbulkdelete hashvacuumcleanup hashcostestimate hashoptions ));
|
||||
DESCR("hash index access method");
|
||||
#define HASH_AM_OID 405
|
||||
DATA(insert OID = 783 ( gist 0 7 f f t t t t t t 0 gistinsert gistbeginscan gistgettuple gistgetbitmap gistrescan gistendscan gistmarkpos gistrestrpos gistbuild gistbulkdelete gistvacuumcleanup gistcostestimate gistoptions ));
|
||||
DATA(insert OID = 783 ( gist 0 7 f f f t t t t t t 0 gistinsert gistbeginscan gistgettuple gistgetbitmap gistrescan gistendscan gistmarkpos gistrestrpos gistbuild gistbulkdelete gistvacuumcleanup gistcostestimate gistoptions ));
|
||||
DESCR("GiST index access method");
|
||||
#define GIST_AM_OID 783
|
||||
DATA(insert OID = 2742 ( gin 0 5 f f t t f f t f 0 gininsert ginbeginscan gingettuple gingetbitmap ginrescan ginendscan ginmarkpos ginrestrpos ginbuild ginbulkdelete ginvacuumcleanup gincostestimate ginoptions ));
|
||||
DATA(insert OID = 2742 ( gin 0 5 f f f t t f f t f 0 gininsert ginbeginscan gingettuple gingetbitmap ginrescan ginendscan ginmarkpos ginrestrpos ginbuild ginbulkdelete ginvacuumcleanup gincostestimate ginoptions ));
|
||||
DESCR("GIN index access method");
|
||||
#define GIN_AM_OID 2742
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue