postgresql/src/backend/optimizer/util/joininfo.c

/*-------------------------------------------------------------------------
 *
 * joininfo.c
 *	  JoinInfo node manipulation routines
 *
 * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/joininfo.c,v 1.33 2003/01/24 03:58:43 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"


/*
 * find_joininfo_node
 *	  Find the joininfo node within a relation entry corresponding
 *	  to a join between 'this_rel' and the relations in 'join_relids'.
 *	  If there is no such node, return NULL.
 *
 * Returns a joininfo node, or NULL.
 */
JoinInfo *
find_joininfo_node(RelOptInfo *this_rel, Relids join_relids)
{
	List	   *i;

	foreach(i, this_rel->joininfo)
	{
		JoinInfo   *joininfo = (JoinInfo *) lfirst(i);

		if (sameseti(join_relids, joininfo->unjoined_relids))
			return joininfo;
	}
	return NULL;
}

/*
 * make_joininfo_node
 *	  Find the joininfo node within a relation entry corresponding
 *	  to a join between 'this_rel' and the relations in 'join_relids'.
 *	  A new node is created and added to the relation entry's joininfo
 *	  field if the desired one can't be found.
 *
 * Returns a joininfo node.
 */
JoinInfo *
make_joininfo_node(RelOptInfo *this_rel, Relids join_relids)
{
	JoinInfo   *joininfo = find_joininfo_node(this_rel, join_relids);

	if (joininfo == NULL)
	{
		joininfo = makeNode(JoinInfo);
		joininfo->unjoined_relids = join_relids;
		joininfo->jinfo_restrictinfo = NIL;
		this_rel->joininfo = lcons(joininfo, this_rel->joininfo);
	}
	return joininfo;
}


/*
 * add_join_clause_to_rels
 *	  For every relation participating in a join clause, add 'restrictinfo' to
 *	  the appropriate joininfo list (creating a new list and adding it to the
 *	  appropriate rel node if necessary).
 *
 * Note that the same copy of the restrictinfo node is linked to by all the
 * lists it is in.  This allows us to exploit caching of information about
 * the restriction clause (but we must be careful that the information does
 * not depend on context).
 *
 * 'restrictinfo' describes the join clause
 * 'join_relids' is the list of relations participating in the join clause
 *				 (there must be more than one)
 */
void
add_join_clause_to_rels(Query *root,
						RestrictInfo *restrictinfo,
						Relids join_relids)
{
	List	   *join_relid;

	/* For every relid, find the joininfo, and add the proper join entries */
	foreach(join_relid, join_relids)
	{
		int			cur_relid = lfirsti(join_relid);
		Relids		unjoined_relids = NIL;
		JoinInfo   *joininfo;
		List	   *otherrel;

		/* Get the relids not equal to the current relid */
		foreach(otherrel, join_relids)
		{
			if (lfirsti(otherrel) != cur_relid)
				unjoined_relids = lappendi(unjoined_relids, lfirsti(otherrel));
		}
		Assert(unjoined_relids != NIL);

		/*
		 * Find or make the joininfo node for this combination of rels,
		 * and add the restrictinfo node to it.
		 */
		joininfo = make_joininfo_node(find_base_rel(root, cur_relid),
									  unjoined_relids);
		joininfo->jinfo_restrictinfo = lappend(joininfo->jinfo_restrictinfo,
											   restrictinfo);
		/*
		 * Can't freeList(unjoined_relids) because new joininfo node may
		 * link to it.  We could avoid leaking memory by doing listCopy()
		 * in make_joininfo_node, but for now speed seems better.
		 */
	}
}

/*
 * remove_join_clause_from_rels
 *	  Delete 'restrictinfo' from all the joininfo lists it is in
 *
 * This reverses the effect of add_join_clause_to_rels.  It's used when we
 * discover that a join clause is redundant.
 *
 * 'restrictinfo' describes the join clause
 * 'join_relids' is the list of relations participating in the join clause
 *				 (there must be more than one)
 */
void
remove_join_clause_from_rels(Query *root,
							 RestrictInfo *restrictinfo,
							 Relids join_relids)
{
	List	   *join_relid;

	/* For every relid, find the joininfo */
	foreach(join_relid, join_relids)
	{
		int			cur_relid = lfirsti(join_relid);
		Relids		unjoined_relids = NIL;
		JoinInfo   *joininfo;
		List	   *otherrel;

		/* Get the relids not equal to the current relid */
		foreach(otherrel, join_relids)
		{
			if (lfirsti(otherrel) != cur_relid)
				unjoined_relids = lappendi(unjoined_relids, lfirsti(otherrel));
		}
		Assert(unjoined_relids != NIL);

		/*
		 * Find the joininfo node for this combination of rels; it should
		 * exist already, if add_join_clause_to_rels was called.
		 */
		joininfo = find_joininfo_node(find_base_rel(root, cur_relid),
									  unjoined_relids);
		Assert(joininfo);
		/*
		 * Remove the restrictinfo from the list.  Pointer comparison
		 * is sufficient.
		 */
		Assert(ptrMember(restrictinfo, joininfo->jinfo_restrictinfo));
		joininfo->jinfo_restrictinfo = lremove(restrictinfo,
											   joininfo->jinfo_restrictinfo);
		freeList(unjoined_relids);
	}
}