get_append_rel_partitions.c

/*
 * get_append_rel_partitions
 *		Return the list of partitions of rel that pass the clauses mentioned
 *		in rel->baserestrictinfo. An empty list is returned if no matching
 *		partitions were found.
 *
 * Returned list contains the AppendRelInfos of chosen partitions.
 */
static List *
get_append_rel_partitions(PlannerInfo *root,
						  RelOptInfo *rel,
						  RangeTblEntry *rte)
{
	List   *partclauses;
	bool	contains_const,
			constfalse;

	/*
	 * Get the clauses that match the partition key, including information
	 * about any nullness tests against partition keys.  Set keynullness to
	 * a invalid value of NullTestType, which 0 is not.
	 */
	partclauses = match_clauses_to_partkey(rel,
										   list_copy(rel->baserestrictinfo),
										   &contains_const,
										   &constfalse);

	if (!constfalse)
	{
		Relation		parent = heap_open(rte->relid, NoLock);
		PartitionDesc	partdesc = RelationGetPartitionDesc(parent);
		Bitmapset	   *partindexes;
		List		   *result = NIL;
		int				i;

		/*
		 * If we have matched clauses that contain at least one constant
		 * operand, then use these to prune partitions.
		 */
		if (partclauses != NIL && contains_const)
			partindexes = get_partitions_from_clauses(parent, partclauses);

		/*
		 * Else there are no clauses that are useful to prune any paritions,
		 * so we must scan all partitions.
		 */
		else
			partindexes = bms_add_range(NULL, 0, partdesc->nparts - 1);

		/* Fetch the partition appinfos. */
		i = -1;
		while ((i = bms_next_member(partindexes, i)) >= 0)
		{
			AppendRelInfo *appinfo = rel->part_appinfos[i];

#ifdef USE_ASSERT_CHECKING
			RangeTblEntry *rte = planner_rt_fetch(appinfo->child_relid, root);

			/*
			 * Must be the intended child's RTE here, because appinfos are ordered
			 * the same way as partitions in the partition descriptor.
			 */
			Assert(partdesc->oids[i] == rte->relid);
#endif

			result = lappend(result, appinfo);
		}

		/* Record which partitions must be scanned. */
		rel->live_part_appinfos = result;

		heap_close(parent, NoLock);

		return result;
	}

	return NIL;
}