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/*-------------------------------------------------------------------------
*
* prune.c
* Routines to prune redundant paths and relations
*
* Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/Attic/prune.c,v 1.43 1999/08/16 02:17:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
static List *merge_rel_with_same_relids(RelOptInfo *rel, List *unmerged_rels);
/*
* merge_rels_with_same_relids
* Removes any redundant relation entries from a list of rel nodes
* 'rel_list', merging their pathlists into the first non-duplicate
* relation entry for each value of relids.
*
* Returns the resulting list.
*/
void
merge_rels_with_same_relids(List *rel_list)
{
List *i;
/*
* rel_list can shorten while running as duplicate relations are
* deleted. Obviously, the first relation can't be a duplicate,
* so the list head pointer won't change.
*/
foreach(i, rel_list)
{
lnext(i) = merge_rel_with_same_relids((RelOptInfo *) lfirst(i),
lnext(i));
}
}
/*
* merge_rel_with_same_relids
* Prunes those relations from 'unmerged_rels' that are redundant with
* 'rel'. A relation is redundant if it is built up of the same
* relations as 'rel'. Paths for the redundant relations are merged into
* the pathlist of 'rel'.
*
* Returns a list of non-redundant relations, and sets the pathlist field
* of 'rel' appropriately.
*
*/
static List *
merge_rel_with_same_relids(RelOptInfo *rel, List *unmerged_rels)
{
List *result = NIL;
List *i;
foreach(i, unmerged_rels)
{
RelOptInfo *unmerged_rel = (RelOptInfo *) lfirst(i);
if (same(rel->relids, unmerged_rel->relids))
{
/*
* These rels are for the same set of base relations,
* so get the best of their pathlists. We assume it's
* ok to reassign a path to the other RelOptInfo without
* doing more than changing its parent pointer (cf. pathnode.c).
*/
rel->pathlist = add_pathlist(rel,
rel->pathlist,
unmerged_rel->pathlist);
}
else
result = lappend(result, unmerged_rel);
}
return result;
}
/*
* rels_set_cheapest
* For each relation entry in 'rel_list' (which should contain only join
* relations), set pointers to the cheapest path and compute rel size.
*/
void
rels_set_cheapest(List *rel_list)
{
List *x;
foreach(x, rel_list)
{
RelOptInfo *rel = (RelOptInfo *) lfirst(x);
JoinPath *cheapest;
cheapest = (JoinPath *) set_cheapest(rel, rel->pathlist);
if (IsA_JoinPath(cheapest))
rel->size = compute_joinrel_size(cheapest);
else
elog(ERROR, "rels_set_cheapest: non JoinPath found");
}
}
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