Function postgresGetForeignRelSize

contrib/postgres_fdw/postgres_fdw.c:622–786

* postgresGetForeignRelSize * Estimate # of rows and width of the result of the scan * * We should consider the effect of all baserestrictinfo clauses here, but * not any join clauses. */

 * not any join clauses.
 */
static void
postgresGetForeignRelSize(PlannerInfo *root,
						  RelOptInfo *baserel,
						  Oid foreigntableid)
{
	PgFdwRelationInfo *fpinfo;
	ListCell   *lc;
	RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);

	/*
	 * We use PgFdwRelationInfo to pass various information to subsequent
	 * functions.
	 */
	fpinfo = (PgFdwRelationInfo *) palloc0(sizeof(PgFdwRelationInfo));
	baserel->fdw_private = (void *) fpinfo;

	/* Base foreign tables need to be pushed down always. */
	fpinfo->pushdown_safe = true;

	/* Look up foreign-table catalog info. */
	fpinfo->table = GetForeignTable(foreigntableid);
	fpinfo->server = GetForeignServer(fpinfo->table->serverid);

	/*
	 * Extract user-settable option values.  Note that per-table settings of
	 * use_remote_estimate, fetch_size and async_capable override per-server
	 * settings of them, respectively.
	 */
	fpinfo->use_remote_estimate = false;
	fpinfo->fdw_startup_cost = DEFAULT_FDW_STARTUP_COST;
	fpinfo->fdw_tuple_cost = DEFAULT_FDW_TUPLE_COST;
	fpinfo->shippable_extensions = NIL;
	fpinfo->fetch_size = 100;
	fpinfo->async_capable = false;

	apply_server_options(fpinfo);
	apply_table_options(fpinfo);

	/*
	 * If the table or the server is configured to use remote estimates,
	 * identify which user to do remote access as during planning.  This
	 * should match what ExecCheckRTEPerms() does.  If we fail due to lack of
	 * permissions, the query would have failed at runtime anyway.
	 */
	if (fpinfo->use_remote_estimate)
	{
		Oid			userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();

		fpinfo->user = GetUserMapping(userid, fpinfo->server->serverid);
	}
	else
		fpinfo->user = NULL;

	/*
	 * Identify which baserestrictinfo clauses can be sent to the remote
	 * server and which can't.
	 */
	classifyConditions(root, baserel, baserel->baserestrictinfo,