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Add an index on pg_inherits.inhparent, and use it to avoid seqscans in
find_inheritance_children(). This is a complete no-op in databases without any inheritance. In databases where there are just a few entries in pg_inherits, it could conceivably be a small loss. However, in databases with many inheritance parents, it can be a big win.
This commit is contained in:
Tom Lane
parent
649b5ec7c8
commit
540e69a061
@ -13,13 +13,15 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.3 2009/06/11 14:48:55 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.4 2009/12/29 22:00:12 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/genam.h"
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#include "access/heapam.h"
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#include "catalog/indexing.h"
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#include "catalog/pg_class.h"
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#include "catalog/pg_inherits.h"
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#include "catalog/pg_inherits_fn.h"
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@ -29,6 +31,8 @@
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#include "utils/syscache.h"
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#include "utils/tqual.h"
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static int oid_cmp(const void *p1, const void *p2);
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/*
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* find_inheritance_children
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@ -46,10 +50,14 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
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{
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List *list = NIL;
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Relation relation;
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HeapScanDesc scan;
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SysScanDesc scan;
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ScanKeyData key[1];
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HeapTuple inheritsTuple;
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Oid inhrelid;
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Oid *oidarr;
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int maxoids,
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numoids,
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i;
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/*
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* Can skip the scan if pg_class shows the relation has never had a
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@ -59,21 +67,52 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
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return NIL;
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/*
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* XXX might be a good idea to create an index on pg_inherits' inhparent
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* field, so that we can use an indexscan instead of sequential scan here.
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* However, in typical databases pg_inherits won't have enough entries to
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* justify an indexscan...
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* Scan pg_inherits and build a working array of subclass OIDs.
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*/
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maxoids = 32;
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oidarr = (Oid *) palloc(maxoids * sizeof(Oid));
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numoids = 0;
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relation = heap_open(InheritsRelationId, AccessShareLock);
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ScanKeyInit(&key[0],
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Anum_pg_inherits_inhparent,
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BTEqualStrategyNumber, F_OIDEQ,
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ObjectIdGetDatum(parentrelId));
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scan = heap_beginscan(relation, SnapshotNow, 1, key);
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while ((inheritsTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
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scan = systable_beginscan(relation, InheritsParentIndexId, true,
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SnapshotNow, 1, key);
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while ((inheritsTuple = systable_getnext(scan)) != NULL)
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{
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inhrelid = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhrelid;
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if (numoids >= maxoids)
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{
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maxoids *= 2;
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oidarr = (Oid *) repalloc(oidarr, maxoids * sizeof(Oid));
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}
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oidarr[numoids++] = inhrelid;
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}
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systable_endscan(scan);
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heap_close(relation, AccessShareLock);
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/*
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* If we found more than one child, sort them by OID. This ensures
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* reasonably consistent behavior regardless of the vagaries of an
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* indexscan. This is important since we need to be sure all backends
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* lock children in the same order to avoid needless deadlocks.
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*/
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if (numoids > 1)
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qsort(oidarr, numoids, sizeof(Oid), oid_cmp);
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/*
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* Acquire locks and build the result list.
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*/
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for (i = 0; i < numoids; i++)
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{
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inhrelid = oidarr[i];
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if (lockmode != NoLock)
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{
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@ -99,8 +138,7 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
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list = lappend_oid(list, inhrelid);
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}
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heap_endscan(scan);
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heap_close(relation, AccessShareLock);
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pfree(oidarr);
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return list;
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}
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@ -231,7 +269,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
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{
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Oid this_relid = lfirst_oid(queue_item);
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ScanKeyData skey;
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HeapScanDesc inhscan;
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SysScanDesc inhscan;
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HeapTuple inhtup;
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/*
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@ -255,9 +293,10 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
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BTEqualStrategyNumber, F_OIDEQ,
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ObjectIdGetDatum(this_relid));
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inhscan = heap_beginscan(inhrel, SnapshotNow, 1, &skey);
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inhscan = systable_beginscan(inhrel, InheritsRelidSeqnoIndexId, true,
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SnapshotNow, 1, &skey);
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while ((inhtup = heap_getnext(inhscan, ForwardScanDirection)) != NULL)
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while ((inhtup = systable_getnext(inhscan)) != NULL)
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{
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Form_pg_inherits inh = (Form_pg_inherits) GETSTRUCT(inhtup);
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Oid inhparent = inh->inhparent;
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@ -273,7 +312,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
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queue = lappend_oid(queue, inhparent);
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}
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heap_endscan(inhscan);
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systable_endscan(inhscan);
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if (result)
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break;
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@ -287,3 +326,18 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
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return result;
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}
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/* qsort comparison function */
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static int
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oid_cmp(const void *p1, const void *p2)
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{
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Oid v1 = *((const Oid *) p1);
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Oid v2 = *((const Oid *) p2);
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if (v1 < v2)
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return -1;
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if (v1 > v2)
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return 1;
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return 0;
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}
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.311 2009/12/23 16:43:43 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.312 2009/12/29 22:00:12 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -1793,8 +1793,8 @@ StoreCatalogInheritance1(Oid relationId, Oid parentOid,
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int16 seqNumber, Relation inhRelation)
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{
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TupleDesc desc = RelationGetDescr(inhRelation);
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Datum datum[Natts_pg_inherits];
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bool nullarr[Natts_pg_inherits];
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Datum values[Natts_pg_inherits];
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bool nulls[Natts_pg_inherits];
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ObjectAddress childobject,
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parentobject;
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HeapTuple tuple;
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@ -1802,15 +1802,13 @@ StoreCatalogInheritance1(Oid relationId, Oid parentOid,
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/*
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* Make the pg_inherits entry
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*/
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datum[0] = ObjectIdGetDatum(relationId); /* inhrelid */
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datum[1] = ObjectIdGetDatum(parentOid); /* inhparent */
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datum[2] = Int16GetDatum(seqNumber); /* inhseqno */
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values[Anum_pg_inherits_inhrelid - 1] = ObjectIdGetDatum(relationId);
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values[Anum_pg_inherits_inhparent - 1] = ObjectIdGetDatum(parentOid);
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values[Anum_pg_inherits_inhseqno - 1] = Int16GetDatum(seqNumber);
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nullarr[0] = false;
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nullarr[1] = false;
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nullarr[2] = false;
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memset(nulls, 0, sizeof(nulls));
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tuple = heap_form_tuple(desc, datum, nullarr);
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tuple = heap_form_tuple(desc, values, nulls);
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simple_heap_insert(inhRelation, tuple);
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@ -37,7 +37,7 @@
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* Portions Copyright (c) 1996-2009, 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 1.562 2009/12/29 20:11:45 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.563 2009/12/29 22:00:14 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 200912281
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#define CATALOG_VERSION_NO 200912291
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#endif
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@ -8,7 +8,7 @@
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* Portions Copyright (c) 1996-2009, 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/indexing.h,v 1.112 2009/12/29 20:11:45 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/indexing.h,v 1.113 2009/12/29 22:00:14 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -156,6 +156,9 @@ DECLARE_UNIQUE_INDEX(pg_index_indexrelid_index, 2679, on pg_index using btree(in
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DECLARE_UNIQUE_INDEX(pg_inherits_relid_seqno_index, 2680, on pg_inherits using btree(inhrelid oid_ops, inhseqno int4_ops));
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#define InheritsRelidSeqnoIndexId 2680
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/* This following index is not used for a cache and is not unique */
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DECLARE_INDEX(pg_inherits_parent_index, 2187, on pg_inherits using btree(inhparent oid_ops));
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#define InheritsParentIndexId 2187
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DECLARE_UNIQUE_INDEX(pg_language_name_index, 2681, on pg_language using btree(lanname name_ops));
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#define LanguageNameIndexId 2681
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