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 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.178 2008/10/06 13:59:37 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.179 2008/10/17 22:10:29 tgl Exp $ -->
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<!--
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Documentation of the system catalogs, directed toward PostgreSQL developers
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-->
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@ -401,6 +401,13 @@
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<entry>Does the access method support ordered scans?</entry>
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</row>
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<row>
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<entry><structfield>amcanbackward</structfield></entry>
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<entry><type>bool</type></entry>
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<entry></entry>
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<entry>Does the access method support backward scanning?</entry>
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</row>
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<row>
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<entry><structfield>amcanunique</structfield></entry>
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<entry><type>bool</type></entry>
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.27 2008/08/14 18:47:58 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.28 2008/10/17 22:10:29 tgl Exp $ -->
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<chapter id="indexam">
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<title>Index Access Method Interface Definition</title>
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@ -474,15 +474,20 @@ amrestrpos (IndexScanDesc scan);
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normally would. (This will only occur for access
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methods that advertise they support ordered scans.) After the
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first call, <function>amgettuple</> must be prepared to advance the scan in
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either direction from the most recently returned entry.
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either direction from the most recently returned entry. (But if
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<structname>pg_am</>.<structfield>amcanbackward</> is false, all subsequent
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calls will have the same direction as the first one.)
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</para>
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<para>
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The access method must support <quote>marking</> a position in a scan
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and later returning to the marked position. The same position might be
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restored multiple times. However, only one position need be remembered
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per scan; a new <function>ammarkpos</> call overrides the previously
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marked position.
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Access methods that support ordered scans must support <quote>marking</> a
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position in a scan and later returning to the marked position. The same
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position might be restored multiple times. However, only one position need
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be remembered per scan; a new <function>ammarkpos</> call overrides the
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previously marked position. An access method that does not support
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ordered scans should still provide mark and restore functions in
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<structname>pg_am</>, but it is sufficient to have them throw errors if
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called.
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</para>
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<para>
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@ -6,7 +6,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.99 2008/10/04 21:56:53 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.100 2008/10/17 22:10:29 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -42,6 +42,12 @@
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#include "executor/nodeValuesscan.h"
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#include "executor/nodeCtescan.h"
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#include "executor/nodeWorktablescan.h"
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#include "nodes/nodeFuncs.h"
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#include "utils/syscache.h"
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static bool TargetListSupportsBackwardScan(List *targetlist);
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static bool IndexSupportsBackwardScan(Oid indexid);
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/*
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@ -390,7 +396,8 @@ ExecSupportsBackwardScan(Plan *node)
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{
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case T_Result:
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if (outerPlan(node) != NULL)
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return ExecSupportsBackwardScan(outerPlan(node));
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return ExecSupportsBackwardScan(outerPlan(node)) &&
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TargetListSupportsBackwardScan(node->targetlist);
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else
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return false;
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@ -403,29 +410,85 @@ ExecSupportsBackwardScan(Plan *node)
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if (!ExecSupportsBackwardScan((Plan *) lfirst(l)))
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return false;
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}
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/* need not check tlist because Append doesn't evaluate it */
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return true;
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}
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case T_SeqScan:
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case T_IndexScan:
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case T_TidScan:
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case T_FunctionScan:
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case T_ValuesScan:
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case T_CteScan:
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case T_WorkTableScan:
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return true;
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return TargetListSupportsBackwardScan(node->targetlist);
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case T_IndexScan:
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return IndexSupportsBackwardScan(((IndexScan *) node)->indexid) &&
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TargetListSupportsBackwardScan(node->targetlist);
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case T_SubqueryScan:
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return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan);
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return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan) &&
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TargetListSupportsBackwardScan(node->targetlist);
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case T_Material:
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case T_Sort:
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/* these don't evaluate tlist */
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return true;
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case T_Limit:
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/* doesn't evaluate tlist */
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return ExecSupportsBackwardScan(outerPlan(node));
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default:
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return false;
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}
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}
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/*
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* If the tlist contains set-returning functions, we can't support backward
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* scan, because the TupFromTlist code is direction-ignorant.
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*/
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static bool
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TargetListSupportsBackwardScan(List *targetlist)
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{
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if (expression_returns_set((Node *) targetlist))
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return false;
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return true;
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}
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/*
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* An IndexScan node supports backward scan only if the index's AM does.
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*/
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static bool
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IndexSupportsBackwardScan(Oid indexid)
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{
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bool result;
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HeapTuple ht_idxrel;
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HeapTuple ht_am;
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Form_pg_class idxrelrec;
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Form_pg_am amrec;
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/* Fetch the pg_class tuple of the index relation */
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ht_idxrel = SearchSysCache(RELOID,
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ObjectIdGetDatum(indexid),
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0, 0, 0);
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if (!HeapTupleIsValid(ht_idxrel))
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elog(ERROR, "cache lookup failed for relation %u", indexid);
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idxrelrec = (Form_pg_class) GETSTRUCT(ht_idxrel);
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/* Fetch the pg_am tuple of the index' access method */
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ht_am = SearchSysCache(AMOID,
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ObjectIdGetDatum(idxrelrec->relam),
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0, 0, 0);
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if (!HeapTupleIsValid(ht_am))
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elog(ERROR, "cache lookup failed for access method %u",
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idxrelrec->relam);
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amrec = (Form_pg_am) GETSTRUCT(ht_am);
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result = amrec->amcanbackward;
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ReleaseSysCache(ht_idxrel);
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ReleaseSysCache(ht_am);
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return result;
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}
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@ -37,7 +37,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.498 2008/10/14 17:12:33 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.499 2008/10/17 22:10:30 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -53,6 +53,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 200810141
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#define CATALOG_VERSION_NO 200810171
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#endif
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@ -8,7 +8,7 @@
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/pg_am.h,v 1.58 2008/09/15 18:43:41 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/pg_am.h,v 1.59 2008/10/17 22:10:30 tgl Exp $
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*
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* NOTES
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* the genbki.sh script reads this file and generates .bki
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@ -41,6 +41,7 @@ CATALOG(pg_am,2601)
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int2 amsupport; /* total number of support functions that this
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* AM uses */
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bool amcanorder; /* does AM support ordered scan results? */
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bool amcanbackward; /* does AM support backward scan? */
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bool amcanunique; /* does AM support UNIQUE indexes? */
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bool amcanmulticol; /* does AM support multi-column indexes? */
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bool amoptionalkey; /* can query omit key for the first column? */
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@ -75,48 +76,49 @@ typedef FormData_pg_am *Form_pg_am;
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* compiler constants for pg_am
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* ----------------
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*/
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#define Natts_pg_am 25
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#define Natts_pg_am 26
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#define Anum_pg_am_amname 1
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#define Anum_pg_am_amstrategies 2
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#define Anum_pg_am_amsupport 3
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#define Anum_pg_am_amcanorder 4
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#define Anum_pg_am_amcanunique 5
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#define Anum_pg_am_amcanmulticol 6
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#define Anum_pg_am_amoptionalkey 7
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#define Anum_pg_am_amindexnulls 8
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#define Anum_pg_am_amsearchnulls 9
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#define Anum_pg_am_amstorage 10
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#define Anum_pg_am_amclusterable 11
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#define Anum_pg_am_amkeytype 12
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#define Anum_pg_am_aminsert 13
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#define Anum_pg_am_ambeginscan 14
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#define Anum_pg_am_amgettuple 15
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#define Anum_pg_am_amgetbitmap 16
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#define Anum_pg_am_amrescan 17
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#define Anum_pg_am_amendscan 18
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#define Anum_pg_am_ammarkpos 19
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#define Anum_pg_am_amrestrpos 20
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#define Anum_pg_am_ambuild 21
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#define Anum_pg_am_ambulkdelete 22
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#define Anum_pg_am_amvacuumcleanup 23
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#define Anum_pg_am_amcostestimate 24
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#define Anum_pg_am_amoptions 25
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#define Anum_pg_am_amcanbackward 5
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#define Anum_pg_am_amcanunique 6
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#define Anum_pg_am_amcanmulticol 7
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#define Anum_pg_am_amoptionalkey 8
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#define Anum_pg_am_amindexnulls 9
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#define Anum_pg_am_amsearchnulls 10
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#define Anum_pg_am_amstorage 11
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#define Anum_pg_am_amclusterable 12
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#define Anum_pg_am_amkeytype 13
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#define Anum_pg_am_aminsert 14
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#define Anum_pg_am_ambeginscan 15
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#define Anum_pg_am_amgettuple 16
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#define Anum_pg_am_amgetbitmap 17
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#define Anum_pg_am_amrescan 18
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#define Anum_pg_am_amendscan 19
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#define Anum_pg_am_ammarkpos 20
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#define Anum_pg_am_amrestrpos 21
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#define Anum_pg_am_ambuild 22
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#define Anum_pg_am_ambulkdelete 23
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#define Anum_pg_am_amvacuumcleanup 24
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#define Anum_pg_am_amcostestimate 25
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#define Anum_pg_am_amoptions 26
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/* ----------------
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* initial contents of pg_am
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* ----------------
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*/
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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 ));
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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 ));
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DESCR("b-tree index access method");
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#define BTREE_AM_OID 403
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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 ));
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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 ));
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DESCR("hash index access method");
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#define HASH_AM_OID 405
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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 ));
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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 ));
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DESCR("GiST index access method");
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#define GIST_AM_OID 783
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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 ));
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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 ));
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DESCR("GIN index access method");
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#define GIN_AM_OID 2742
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