Function postgresReScanForeignScan

contrib/postgres_fdw/postgres_fdw.c:1643–1705

* postgresReScanForeignScan * Restart the scan. */

 *		Restart the scan.
 */
static void
postgresReScanForeignScan(ForeignScanState *node)
{
	PgFdwScanState *fsstate = (PgFdwScanState *) node->fdw_state;
	char		sql[64];
	PGresult   *res;

	/* If we haven't created the cursor yet, nothing to do. */
	if (!fsstate->cursor_exists)
		return;

	/*
	 * If the node is async-capable, and an asynchronous fetch for it has been
	 * begun, the asynchronous fetch might not have yet completed.  Check if
	 * the node is async-capable, and an asynchronous fetch for it is still in
	 * progress; if so, complete the asynchronous fetch before restarting the
	 * scan.
	 */
	if (fsstate->async_capable &&
		fsstate->conn_state->pendingAreq &&
		fsstate->conn_state->pendingAreq->requestee == (PlanState *) node)
		fetch_more_data(node);

	/*
	 * If any internal parameters affecting this node have changed, we'd
	 * better destroy and recreate the cursor.  Otherwise, rewinding it should
	 * be good enough.  If we've only fetched zero or one batch, we needn't
	 * even rewind the cursor, just rescan what we have.
	 */
	if (node->ss.ps.chgParam != NULL)
	{
		fsstate->cursor_exists = false;
		snprintf(sql, sizeof(sql), "CLOSE c%u",
				 fsstate->cursor_number);
	}
	else if (fsstate->fetch_ct_2 > 1)
	{
		snprintf(sql, sizeof(sql), "MOVE BACKWARD ALL IN c%u",
				 fsstate->cursor_number);
	}
	else
	{
		/* Easy: just rescan what we already have in memory, if anything */
		fsstate->next_tuple = 0;
		return;
	}

	/*
	 * We don't use a PG_TRY block here, so be careful not to throw error
	 * without releasing the PGresult.
	 */
	res = pgfdw_exec_query(fsstate->conn, sql, fsstate->conn_state);
	if (PQresultStatus(res) != PGRES_COMMAND_OK)
		pgfdw_report_error(ERROR, res, fsstate->conn, true, sql);
	PQclear(res);

	/* Now force a fresh FETCH. */
	fsstate->tuples = NULL;