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Add an index on pg_inherits.inhparent, and use it to avoid seqscans in

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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
2009-12-29 22:00:14 +00:00
parent 649b5ec7c8
commit 540e69a061
4 changed files with 82 additions and 27 deletions
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82
src/backend/catalog/pg_inherits.c
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@@ -13,13 +13,15 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.3 2009/06/11 14:48:55 momjian Exp $
* $PostgreSQL: pgsql/src/backend/catalog/pg_inherits.c,v 1.4 2009/12/29 22:00:12 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/heapam.h"
#include "catalog/indexing.h"
#include "catalog/pg_class.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_inherits_fn.h"
@@ -29,6 +31,8 @@
#include "utils/syscache.h"
#include "utils/tqual.h"
static int oid_cmp(const void *p1, const void *p2);
/*
* find_inheritance_children
@@ -46,10 +50,14 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
{
List *list = NIL;
Relation relation;
HeapScanDesc scan;
SysScanDesc scan;
ScanKeyData key[1];
HeapTuple inheritsTuple;
Oid inhrelid;
Oid *oidarr;
int maxoids,
numoids,
i;
/*
* 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)
return NIL;
/*
* XXX might be a good idea to create an index on pg_inherits' inhparent
* field, so that we can use an indexscan instead of sequential scan here.
* However, in typical databases pg_inherits won't have enough entries to
* justify an indexscan...
* Scan pg_inherits and build a working array of subclass OIDs.
*/
maxoids = 32;
oidarr = (Oid *) palloc(maxoids * sizeof(Oid));
numoids = 0;
relation = heap_open(InheritsRelationId, AccessShareLock);
ScanKeyInit(&key[0],
Anum_pg_inherits_inhparent,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(parentrelId));
scan = heap_beginscan(relation, SnapshotNow, 1, key);
while ((inheritsTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
scan = systable_beginscan(relation, InheritsParentIndexId, true,
SnapshotNow, 1, key);
while ((inheritsTuple = systable_getnext(scan)) != NULL)
{
inhrelid = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhrelid;
if (numoids >= maxoids)
{
maxoids *= 2;
oidarr = (Oid *) repalloc(oidarr, maxoids * sizeof(Oid));
}
oidarr[numoids++] = inhrelid;
}
systable_endscan(scan);
heap_close(relation, AccessShareLock);
/*
* If we found more than one child, sort them by OID. This ensures
* reasonably consistent behavior regardless of the vagaries of an
* indexscan. This is important since we need to be sure all backends
* lock children in the same order to avoid needless deadlocks.
*/
if (numoids > 1)
qsort(oidarr, numoids, sizeof(Oid), oid_cmp);
/*
* Acquire locks and build the result list.
*/
for (i = 0; i < numoids; i++)
{
inhrelid = oidarr[i];
if (lockmode != NoLock)
{
@@ -99,8 +138,7 @@ find_inheritance_children(Oid parentrelId, LOCKMODE lockmode)
list = lappend_oid(list, inhrelid);
}
heap_endscan(scan);
heap_close(relation, AccessShareLock);
pfree(oidarr);
return list;
}
@@ -231,7 +269,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
{
Oid this_relid = lfirst_oid(queue_item);
ScanKeyData skey;
HeapScanDesc inhscan;
SysScanDesc inhscan;
HeapTuple inhtup;
/*
@@ -255,9 +293,10 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(this_relid));
inhscan = heap_beginscan(inhrel, SnapshotNow, 1, &skey);
inhscan = systable_beginscan(inhrel, InheritsRelidSeqnoIndexId, true,
SnapshotNow, 1, &skey);
while ((inhtup = heap_getnext(inhscan, ForwardScanDirection)) != NULL)
while ((inhtup = systable_getnext(inhscan)) != NULL)
{
Form_pg_inherits inh = (Form_pg_inherits) GETSTRUCT(inhtup);
Oid inhparent = inh->inhparent;
@@ -273,7 +312,7 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
queue = lappend_oid(queue, inhparent);
}
heap_endscan(inhscan);
systable_endscan(inhscan);
if (result)
break;
@@ -287,3 +326,18 @@ typeInheritsFrom(Oid subclassTypeId, Oid superclassTypeId)
return result;
}
/* qsort comparison function */
static int
oid_cmp(const void *p1, const void *p2)
{
Oid v1 = *((const Oid *) p1);
Oid v2 = *((const Oid *) p2);
if (v1 < v2)
return -1;
if (v1 > v2)
return 1;
return 0;
}