]> granicus.if.org Git - postgresql/commitdiff
Add an index on pg_inherits.inhparent, and use it to avoid seqscans in
authorTom Lane <tgl@sss.pgh.pa.us>
Tue, 29 Dec 2009 22:00:14 +0000 (22:00 +0000)
committerTom Lane <tgl@sss.pgh.pa.us>
Tue, 29 Dec 2009 22:00:14 +0000 (22:00 +0000)
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.

src/backend/catalog/pg_inherits.c
src/backend/commands/tablecmds.c
src/include/catalog/catversion.h
src/include/catalog/indexing.h

index 8ae368b74132dca2ab0dc98fcbab70e653199355..4106417fb3176266c4b6044ffc235bf1f6999478 100644 (file)
  *
  *
  * 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;
+}
index 559547380886064a70b64e5be84e76410198c450..0412aaf73f2c32f46403e07ebaa2c238274c1794 100644 (file)
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.311 2009/12/23 16:43:43 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.312 2009/12/29 22:00:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1793,8 +1793,8 @@ StoreCatalogInheritance1(Oid relationId, Oid parentOid,
                                                 int16 seqNumber, Relation inhRelation)
 {
        TupleDesc       desc = RelationGetDescr(inhRelation);
-       Datum           datum[Natts_pg_inherits];
-       bool            nullarr[Natts_pg_inherits];
+       Datum           values[Natts_pg_inherits];
+       bool            nulls[Natts_pg_inherits];
        ObjectAddress childobject,
                                parentobject;
        HeapTuple       tuple;
@@ -1802,15 +1802,13 @@ StoreCatalogInheritance1(Oid relationId, Oid parentOid,
        /*
         * Make the pg_inherits entry
         */
-       datum[0] = ObjectIdGetDatum(relationId);        /* inhrelid */
-       datum[1] = ObjectIdGetDatum(parentOid);         /* inhparent */
-       datum[2] = Int16GetDatum(seqNumber);            /* inhseqno */
+       values[Anum_pg_inherits_inhrelid - 1] = ObjectIdGetDatum(relationId);
+       values[Anum_pg_inherits_inhparent - 1] = ObjectIdGetDatum(parentOid);
+       values[Anum_pg_inherits_inhseqno - 1] = Int16GetDatum(seqNumber);
 
-       nullarr[0] = false;
-       nullarr[1] = false;
-       nullarr[2] = false;
+       memset(nulls, 0, sizeof(nulls));
 
-       tuple = heap_form_tuple(desc, datum, nullarr);
+       tuple = heap_form_tuple(desc, values, nulls);
 
        simple_heap_insert(inhRelation, tuple);
 
index 0c4ce005295f3907a457be959188c4ef7cf6d496..05ee9590260ea489e81c44e1124b6eb142fbe743 100644 (file)
@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.562 2009/12/29 20:11:45 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.563 2009/12/29 22:00:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*                                                     yyyymmddN */
-#define CATALOG_VERSION_NO     200912281
+#define CATALOG_VERSION_NO     200912291
 
 #endif
index a5d93ed4455545c80f18b19581e3b19a36a6542f..a7ab8721c7a00dac8f20b0a993b1cd465b96ff1d 100644 (file)
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/indexing.h,v 1.112 2009/12/29 20:11:45 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/indexing.h,v 1.113 2009/12/29 22:00:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -156,6 +156,9 @@ DECLARE_UNIQUE_INDEX(pg_index_indexrelid_index, 2679, on pg_index using btree(in
 
 DECLARE_UNIQUE_INDEX(pg_inherits_relid_seqno_index, 2680, on pg_inherits using btree(inhrelid oid_ops, inhseqno int4_ops));
 #define InheritsRelidSeqnoIndexId  2680
+/* This following index is not used for a cache and is not unique */
+DECLARE_INDEX(pg_inherits_parent_index, 2187, on pg_inherits using btree(inhparent oid_ops));
+#define InheritsParentIndexId  2187
 
 DECLARE_UNIQUE_INDEX(pg_language_name_index, 2681, on pg_language using btree(lanname name_ops));
 #define LanguageNameIndexId  2681