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Make inheritance planning logic a little simpler and clearer,

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hopefully even a little faster.
This commit is contained in:
Tom Lane
2000-06-20 04:22:21 +00:00
parent 996659f255
commit 38db5fab29
4 changed files with 145 additions and 116 deletions
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30
src/backend/optimizer/util/plancat.c
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@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/plancat.c,v 1.57 2000/06/17 21:48:51 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/plancat.c,v 1.58 2000/06/20 04:22:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -261,6 +261,11 @@ join_selectivity(Oid functionObjectId,
*
* Returns an integer list containing the OIDs of all relations which
* inherit *directly* from the relation with OID 'inhparent'.
*
* 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...
*/
List *
find_inheritance_children(Oid inhparent)
@@ -269,12 +274,19 @@ find_inheritance_children(Oid inhparent)
{0, Anum_pg_inherits_inhparent, F_OIDEQ}
};
HeapTuple inheritsTuple;
List *list = NIL;
Relation relation;
HeapScanDesc scan;
List *list = NIL;
HeapTuple inheritsTuple;
Oid inhrelid;
/*
* Can skip the scan if pg_class shows the relation has never had
* a subclass.
*/
if (! has_subclass(inhparent))
return NIL;
fmgr_info(F_OIDEQ, &key[0].sk_func);
key[0].sk_nargs = key[0].sk_func.fn_nargs;
key[0].sk_argument = ObjectIdGetDatum(inhparent);
@@ -292,14 +304,16 @@ find_inheritance_children(Oid inhparent)
}
/*
* has_subclass -
* has_subclass
*
* In the current implementation, has_subclass returns whether a
* particular class *might* have a subclass. It will not return the
* correct result if a class had a subclass which was later dropped.
* This is because relhassubclass in pg_class is not updated,
* possibly because of efficiency and/or concurrency concerns.
* Currently has_subclass is only used as an efficiency hack, so this
* is ok.
* This is because relhassubclass in pg_class is not updated when a
* subclass is dropped, primarily because of concurrency concerns.
*
* Currently has_subclass is only used as an efficiency hack to skip
* unnecessary inheritance searches, so this is OK.
*/
bool
has_subclass(Oid relationId)