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Commit540e69a

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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 withoutany inheritance. In databases where there are just a few entries inpg_inherits, it could conceivably be a small loss. However, in databases withmany inheritance parents, it can be a big win.
1 parent649b5ec commit540e69a

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4 files changed

+82
-27
lines changed

4 files changed

+82
-27
lines changed

‎src/backend/catalog/pg_inherits.c

Lines changed: 68 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -13,13 +13,15 @@
1313
*
1414
*
1515
* IDENTIFICATION
16-
* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.3 2009/06/11 14:48:55 momjian Exp $
16+
* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.4 2009/12/29 22:00:12 tgl Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
2020
#include"postgres.h"
2121

22+
#include"access/genam.h"
2223
#include"access/heapam.h"
24+
#include"catalog/indexing.h"
2325
#include"catalog/pg_class.h"
2426
#include"catalog/pg_inherits.h"
2527
#include"catalog/pg_inherits_fn.h"
@@ -29,6 +31,8 @@
2931
#include"utils/syscache.h"
3032
#include"utils/tqual.h"
3133

34+
staticintoid_cmp(constvoid*p1,constvoid*p2);
35+
3236

3337
/*
3438
* find_inheritance_children
@@ -46,10 +50,14 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
4650
{
4751
List*list=NIL;
4852
Relationrelation;
49-
HeapScanDescscan;
53+
SysScanDescscan;
5054
ScanKeyDatakey[1];
5155
HeapTupleinheritsTuple;
5256
Oidinhrelid;
57+
Oid*oidarr;
58+
intmaxoids,
59+
numoids,
60+
i;
5361

5462
/*
5563
* Can skip the scan if pg_class shows the relation has never had a
@@ -59,21 +67,52 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
5967
returnNIL;
6068

6169
/*
62-
* XXX might be a good idea to create an index on pg_inherits' inhparent
63-
* field, so that we can use an indexscan instead of sequential scan here.
64-
* However, in typical databases pg_inherits won't have enough entries to
65-
* justify an indexscan...
70+
* Scan pg_inherits and build a working array of subclass OIDs.
6671
*/
72+
maxoids=32;
73+
oidarr= (Oid*)palloc(maxoids*sizeof(Oid));
74+
numoids=0;
75+
6776
relation=heap_open(InheritsRelationId,AccessShareLock);
77+
6878
ScanKeyInit(&key[0],
6979
Anum_pg_inherits_inhparent,
7080
BTEqualStrategyNumber,F_OIDEQ,
7181
ObjectIdGetDatum(parentrelId));
72-
scan=heap_beginscan(relation,SnapshotNow,1,key);
7382

74-
while ((inheritsTuple=heap_getnext(scan,ForwardScanDirection))!=NULL)
83+
scan=systable_beginscan(relation,InheritsParentIndexId, true,
84+
SnapshotNow,1,key);
85+
86+
while ((inheritsTuple=systable_getnext(scan))!=NULL)
7587
{
7688
inhrelid= ((Form_pg_inherits)GETSTRUCT(inheritsTuple))->inhrelid;
89+
if (numoids >=maxoids)
90+
{
91+
maxoids *=2;
92+
oidarr= (Oid*)repalloc(oidarr,maxoids*sizeof(Oid));
93+
}
94+
oidarr[numoids++]=inhrelid;
95+
}
96+
97+
systable_endscan(scan);
98+
99+
heap_close(relation,AccessShareLock);
100+
101+
/*
102+
* If we found more than one child, sort them by OID. This ensures
103+
* reasonably consistent behavior regardless of the vagaries of an
104+
* indexscan. This is important since we need to be sure all backends
105+
* lock children in the same order to avoid needless deadlocks.
106+
*/
107+
if (numoids>1)
108+
qsort(oidarr,numoids,sizeof(Oid),oid_cmp);
109+
110+
/*
111+
* Acquire locks and build the result list.
112+
*/
113+
for (i=0;i<numoids;i++)
114+
{
115+
inhrelid=oidarr[i];
77116

78117
if (lockmode!=NoLock)
79118
{
@@ -99,8 +138,7 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
99138
list=lappend_oid(list,inhrelid);
100139
}
101140

102-
heap_endscan(scan);
103-
heap_close(relation,AccessShareLock);
141+
pfree(oidarr);
104142

105143
returnlist;
106144
}
@@ -231,7 +269,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
231269
{
232270
Oidthis_relid=lfirst_oid(queue_item);
233271
ScanKeyDataskey;
234-
HeapScanDescinhscan;
272+
SysScanDescinhscan;
235273
HeapTupleinhtup;
236274

237275
/*
@@ -255,9 +293,10 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
255293
BTEqualStrategyNumber,F_OIDEQ,
256294
ObjectIdGetDatum(this_relid));
257295

258-
inhscan=heap_beginscan(inhrel,SnapshotNow,1,&skey);
296+
inhscan=systable_beginscan(inhrel,InheritsRelidSeqnoIndexId, true,
297+
SnapshotNow,1,&skey);
259298

260-
while ((inhtup=heap_getnext(inhscan,ForwardScanDirection))!=NULL)
299+
while ((inhtup=systable_getnext(inhscan))!=NULL)
261300
{
262301
Form_pg_inheritsinh= (Form_pg_inherits)GETSTRUCT(inhtup);
263302
Oidinhparent=inh->inhparent;
@@ -273,7 +312,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
273312
queue=lappend_oid(queue,inhparent);
274313
}
275314

276-
heap_endscan(inhscan);
315+
systable_endscan(inhscan);
277316

278317
if (result)
279318
break;
@@ -287,3 +326,18 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
287326

288327
returnresult;
289328
}
329+
330+
331+
/* qsort comparison function */
332+
staticint
333+
oid_cmp(constvoid*p1,constvoid*p2)
334+
{
335+
Oidv1=*((constOid*)p1);
336+
Oidv2=*((constOid*)p2);
337+
338+
if (v1<v2)
339+
return-1;
340+
if (v1>v2)
341+
return1;
342+
return0;
343+
}

‎src/backend/commands/tablecmds.c

Lines changed: 8 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.311 2009/12/23 16:43:43 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.312 2009/12/29 22:00:12 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -1793,24 +1793,22 @@ StoreCatalogInheritance1(Oid relationId, Oid parentOid,
17931793
int16seqNumber,RelationinhRelation)
17941794
{
17951795
TupleDescdesc=RelationGetDescr(inhRelation);
1796-
Datumdatum[Natts_pg_inherits];
1797-
boolnullarr[Natts_pg_inherits];
1796+
Datumvalues[Natts_pg_inherits];
1797+
boolnulls[Natts_pg_inherits];
17981798
ObjectAddresschildobject,
17991799
parentobject;
18001800
HeapTupletuple;
18011801

18021802
/*
18031803
* Make the pg_inherits entry
18041804
*/
1805-
datum[0]=ObjectIdGetDatum(relationId);/* inhrelid */
1806-
datum[1]=ObjectIdGetDatum(parentOid);/* inhparent */
1807-
datum[2]=Int16GetDatum(seqNumber);/* inhseqno */
1805+
values[Anum_pg_inherits_inhrelid-1]=ObjectIdGetDatum(relationId);
1806+
values[Anum_pg_inherits_inhparent-1]=ObjectIdGetDatum(parentOid);
1807+
values[Anum_pg_inherits_inhseqno-1]=Int16GetDatum(seqNumber);
18081808

1809-
nullarr[0]= false;
1810-
nullarr[1]= false;
1811-
nullarr[2]= false;
1809+
memset(nulls,0,sizeof(nulls));
18121810

1813-
tuple=heap_form_tuple(desc,datum,nullarr);
1811+
tuple=heap_form_tuple(desc,values,nulls);
18141812

18151813
simple_heap_insert(inhRelation,tuple);
18161814

‎src/include/catalog/catversion.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
3838
* Portions Copyright (c) 1994, Regents of the University of California
3939
*
40-
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.562 2009/12/2920:11:45 tgl Exp $
40+
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.563 2009/12/2922:00:14 tgl Exp $
4141
*
4242
*-------------------------------------------------------------------------
4343
*/
@@ -53,6 +53,6 @@
5353
*/
5454

5555
/*yyyymmddN */
56-
#defineCATALOG_VERSION_NO200912281
56+
#defineCATALOG_VERSION_NO200912291
5757

5858
#endif

‎src/include/catalog/indexing.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
99
* Portions Copyright (c) 1994, Regents of the University of California
1010
*
11-
* $PostgreSQL: pgsql/src/include/catalog/indexing.h,v 1.112 2009/12/2920:11:45 tgl Exp $
11+
* $PostgreSQL: pgsql/src/include/catalog/indexing.h,v 1.113 2009/12/2922:00:14 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -156,6 +156,9 @@ DECLARE_UNIQUE_INDEX(pg_index_indexrelid_index, 2679, on pg_index using btree(in
156156

157157
DECLARE_UNIQUE_INDEX(pg_inherits_relid_seqno_index,2680,onpg_inheritsusingbtree(inhrelidoid_ops,inhseqnoint4_ops));
158158
#defineInheritsRelidSeqnoIndexId 2680
159+
/* This following index is not used for a cache and is not unique */
160+
DECLARE_INDEX(pg_inherits_parent_index,2187,onpg_inheritsusingbtree(inhparentoid_ops));
161+
#defineInheritsParentIndexId 2187
159162

160163
DECLARE_UNIQUE_INDEX(pg_language_name_index,2681,onpg_languageusingbtree(lannamename_ops));
161164
#defineLanguageNameIndexId 2681

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