Function create_cursor

contrib/postgres_fdw/postgres_fdw.c:3716–3787

* Create cursor for node's query with current parameter values. */

 * Create cursor for node's query with current parameter values.
 */
static void
create_cursor(ForeignScanState *node)
{
	PgFdwScanState *fsstate = (PgFdwScanState *) node->fdw_state;
	ExprContext *econtext = node->ss.ps.ps_ExprContext;
	int			numParams = fsstate->numParams;
	const char **values = fsstate->param_values;
	PGconn	   *conn = fsstate->conn;
	StringInfoData buf;
	PGresult   *res;

	/* First, process a pending asynchronous request, if any. */
	if (fsstate->conn_state->pendingAreq)
		process_pending_request(fsstate->conn_state->pendingAreq);

	/*
	 * Construct array of query parameter values in text format.  We do the
	 * conversions in the short-lived per-tuple context, so as not to cause a
	 * memory leak over repeated scans.
	 */
	if (numParams > 0)
	{
		MemoryContext oldcontext;

		oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

		process_query_params(econtext,
							 fsstate->param_flinfo,
							 fsstate->param_exprs,
							 values);

		MemoryContextSwitchTo(oldcontext);
	}

	/* Construct the DECLARE CURSOR command */
	initStringInfo(&buf);
	appendStringInfo(&buf, "DECLARE c%u CURSOR FOR\n%s",
					 fsstate->cursor_number, fsstate->query);

	/*
	 * Notice that we pass NULL for paramTypes, thus forcing the remote server
	 * to infer types for all parameters.  Since we explicitly cast every
	 * parameter (see deparse.c), the "inference" is trivial and will produce
	 * the desired result.  This allows us to avoid assuming that the remote
	 * server has the same OIDs we do for the parameters' types.
	 */
	if (!PQsendQueryParams(conn, buf.data, numParams,
						   NULL, values, NULL, NULL, 0))
		pgfdw_report_error(ERROR, NULL, conn, false, buf.data);

	/*
	 * Get the result, and check for success.
	 *
	 * We don't use a PG_TRY block here, so be careful not to throw error
	 * without releasing the PGresult.
	 */
	res = pgfdw_get_result(conn, buf.data);
	if (PQresultStatus(res) != PGRES_COMMAND_OK)