Function postgresBeginForeignScan

contrib/postgres_fdw/postgres_fdw.c:1491–1591

* postgresBeginForeignScan * Initiate an executor scan of a foreign PostgreSQL table. */

 *		Initiate an executor scan of a foreign PostgreSQL table.
 */
static void
postgresBeginForeignScan(ForeignScanState *node, int eflags)
{
	ForeignScan *fsplan = (ForeignScan *) node->ss.ps.plan;
	EState	   *estate = node->ss.ps.state;
	PgFdwScanState *fsstate;
	RangeTblEntry *rte;
	Oid			userid;
	ForeignTable *table;
	UserMapping *user;
	int			rtindex;
	int			numParams;

	/*
	 * Do nothing in EXPLAIN (no ANALYZE) case.  node->fdw_state stays NULL.
	 */
	if (eflags & EXEC_FLAG_EXPLAIN_ONLY)
		return;

	/*
	 * We'll save private state in node->fdw_state.
	 */
	fsstate = (PgFdwScanState *) palloc0(sizeof(PgFdwScanState));
	node->fdw_state = (void *) fsstate;

	/*
	 * Identify which user to do the remote access as.  This should match what
	 * ExecCheckRTEPerms() does.  In case of a join or aggregate, use the
	 * lowest-numbered member RTE as a representative; we would get the same
	 * result from any.
	 */
	if (fsplan->scan.scanrelid > 0)
		rtindex = fsplan->scan.scanrelid;
	else
		rtindex = bms_next_member(fsplan->fs_relids, -1);
	rte = exec_rt_fetch(rtindex, estate);
	userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();

	/* Get info about foreign table. */
	table = GetForeignTable(rte->relid);
	user = GetUserMapping(userid, table->serverid);

	/*
	 * Get connection to the foreign server.  Connection manager will
	 * establish new connection if necessary.
	 */
	fsstate->conn = GetConnection(user, false, &fsstate->conn_state);

	/* Assign a unique ID for my cursor */
	fsstate->cursor_number = GetCursorNumber(fsstate->conn);
	fsstate->cursor_exists = false;

	/* Get private info created by planner functions. */
	fsstate->query = strVal(list_nth(fsplan->fdw_private,
									 FdwScanPrivateSelectSql));
	fsstate->retrieved_attrs = (List *) list_nth(fsplan->fdw_private,
												 FdwScanPrivateRetrievedAttrs);
	fsstate->fetch_size = intVal(list_nth(fsplan->fdw_private,