Re: RFC: Async query processing

On 01/03/2014 06:06 PM, Claudio Freire wrote:

> Per-query expectations could be such a thing. And it can even work with PQexec:
>
> PQexec(con, "SELECT nextval('a_id_seq') FROM generate_series(1,10);");
> --read--
> PQexec(con, "SELECT nextval('b_id_seq') FROM generate_series(1,10);");
> --read--
> PQexec(con, "INSERT INTO a (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO b (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO a (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO b (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO a (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO b (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> ... 9 times...
> PQexec(con, "INSERT INTO a (...);", PQEXPECT_NO_RESULT | PQASYNC_CORK);
> PQexec(con, "INSERT INTO b (...);", PQEXPECT_NO_RESULT | PQASYNC);
> do {
>     // do something useful
> } while (PQflush());
>
> Here, the PQASYNC flag would temporarily switch to non-blocking I/O,
> and buffer what cannot be sent. PQASNC_CORK, would only buffer (only
> send if the buffer is full). After any ASYNC call, PQflush would be
> necessary (to flush the send queue and to consume the expected
> responses), but I can imagine any synchronous call (PQexec,
> PQsendQuery or whatever) could detect a non-empty buffer and just
> blockingly flush right there.

How would you consume results once they arrive?  I think this only 
covers the no-result case, and it has since come to my attention that 
the Node.js folks are looking for general async response processing.

(In order to implement your proposal, we'd have to add quite a few 
additional APIs to include the flag argument, but that's a minor detail.)

-- 
Florian Weimer / Red Hat Product Security Team