Function fetch_more_data

contrib/postgres_fdw/postgres_fdw.c:3792–3878

* Fetch some more rows from the node's cursor. */

 * Fetch some more rows from the node's cursor.
 */
static void
fetch_more_data(ForeignScanState *node)
{
	PgFdwScanState *fsstate = (PgFdwScanState *) node->fdw_state;
	PGresult   *volatile res = NULL;
	MemoryContext oldcontext;

	/*
	 * We'll store the tuples in the batch_cxt.  First, flush the previous
	 * batch.
	 */
	fsstate->tuples = NULL;
	MemoryContextReset(fsstate->batch_cxt);
	oldcontext = MemoryContextSwitchTo(fsstate->batch_cxt);

	/* PGresult must be released before leaving this function. */
	PG_TRY();
	{
		PGconn	   *conn = fsstate->conn;
		int			numrows;
		int			i;

		if (fsstate->async_capable)
		{
			Assert(fsstate->conn_state->pendingAreq);

			/*
			 * The query was already sent by an earlier call to
			 * fetch_more_data_begin.  So now we just fetch the result.
			 */
			res = pgfdw_get_result(conn, fsstate->query);
			/* On error, report the original query, not the FETCH. */
			if (PQresultStatus(res) != PGRES_TUPLES_OK)
				pgfdw_report_error(ERROR, res, conn, false, fsstate->query);

			/* Reset per-connection state */
			fsstate->conn_state->pendingAreq = NULL;
		}
		else
		{
			char		sql[64];

			/* This is a regular synchronous fetch. */
			snprintf(sql, sizeof(sql), "FETCH %d FROM c%u",
					 fsstate->fetch_size, fsstate->cursor_number);

			res = pgfdw_exec_query(conn, sql, fsstate->conn_state);
			/* On error, report the original query, not the FETCH. */
			if (PQresultStatus(res) != PGRES_TUPLES_OK)
				pgfdw_report_error(ERROR, res, conn, false, fsstate->query);
		}

		/* Convert the data into HeapTuples */
		numrows = PQntuples(res);
		fsstate->tuples = (HeapTuple *) palloc0(numrows * sizeof(HeapTuple));
		fsstate->num_tuples = numrows;
		fsstate->next_tuple = 0;