Function build_paths_for_OR

src/backend/optimizer/path/indxpath.c:1202–1285

* build_paths_for_OR * Given a list of restriction clauses from one arm of an OR clause, * construct all matching IndexPaths for the relation. * * Here we must scan all indexes of the relation, since a bitmap OR tree * can use multiple indexes. * * The caller actually supplies two lists of restriction clauses: some * "current" ones and some "other" ones. Both lists can be used freely

 * 'other_clauses' is the list of additional upper-level clauses
 */
static List *
build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
				   List *clauses, List *other_clauses)
{
	List	   *result = NIL;
	List	   *all_clauses = NIL;	/* not computed till needed */
	ListCell   *lc;

	foreach(lc, rel->indexlist)
	{
		IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
		IndexClauseSet clauseset;
		List	   *indexpaths;
		bool		useful_predicate;

		/* Ignore index if it doesn't support bitmap scans */
		if (!index->amhasgetbitmap)
			continue;

		/*
		 * Ignore partial indexes that do not match the query.  If a partial
		 * index is marked predOK then we know it's OK.  Otherwise, we have to
		 * test whether the added clauses are sufficient to imply the
		 * predicate. If so, we can use the index in the current context.
		 *
		 * We set useful_predicate to true iff the predicate was proven using
		 * the current set of clauses.  This is needed to prevent matching a
		 * predOK index to an arm of an OR, which would be a legal but
		 * pointlessly inefficient plan.  (A better plan will be generated by
		 * just scanning the predOK index alone, no OR.)
		 */
		useful_predicate = false;
		if (index->indpred != NIL)
		{
			if (index->predOK)
			{
				/* Usable, but don't set useful_predicate */
			}
			else
			{
				/* Form all_clauses if not done already */
				if (all_clauses == NIL)
					all_clauses = list_concat_copy(clauses, other_clauses);

				if (!predicate_implied_by(index->indpred, all_clauses, false))
					continue;	/* can't use it at all */

				if (!predicate_implied_by(index->indpred, other_clauses, false))
					useful_predicate = true;
			}
		}

		/*
		 * Identify the restriction clauses that can match the index.
		 */
		MemSet(&clauseset, 0, sizeof(clauseset));
		match_clauses_to_index(root, clauses, index, &clauseset);