(PHP 5 >= 5.6.0, PHP 7)
pg_flush — Flush outbound query data on the connection
pg_flush() flushes any outbound query data waiting to be sent on the connection.
PostgreSQL database connection resource.
TRUE if the flush was successful or no data was waiting to be
flushed, 0 if part of the pending data was flushed but
more remains 或者在失败时返回