Обсуждение: batching commands with libpq

hi,

is there any way to send multiple commands together (ideally in a single
network packet), and then wait for their results, using libpq?  i want to
save extra round-trips.  while postgresql's fe-be on-wire protocol seems
to allow it (is it right?), i couldn't find a way with libpq.

PQsendQuery(conn, "select timeofday();select timeofday();select timeofday();");
seems to work, but i want to use extended protocol.

YAMAMOTO Takashi

yamt@mwd.biglobe.ne.jp (YAMAMOTO Takashi) writes:
> is there any way to send multiple commands together (ideally in a single
> network packet), and then wait for their results, using libpq?  i want to
> save extra round-trips.  while postgresql's fe-be on-wire protocol seems
> to allow it (is it right?), i couldn't find a way with libpq.

> PQsendQuery(conn, "select timeofday();select timeofday();select timeofday();");
> seems to work, but i want to use extended protocol.

You're out of luck: extended protocol intentionally doesn't allow
multiple queries per string.

The wire protocol does in theory allow you to send more commands before
waiting for the results of the first one, but that's not supported in
libpq.  The only case you can do in libpq is multiple commands in a
PQexec string.

            regards, tom lane

hi,

> yamt@mwd.biglobe.ne.jp (YAMAMOTO Takashi) writes:
>> is there any way to send multiple commands together (ideally in a single
>> network packet), and then wait for their results, using libpq?  i want to
>> save extra round-trips.  while postgresql's fe-be on-wire protocol seems
>> to allow it (is it right?), i couldn't find a way with libpq.
>
>> PQsendQuery(conn, "select timeofday();select timeofday();select timeofday();");
>> seems to work, but i want to use extended protocol.
>
> You're out of luck: extended protocol intentionally doesn't allow
> multiple queries per string.
>
> The wire protocol does in theory allow you to send more commands before
> waiting for the results of the first one, but that's not supported in
> libpq.  The only case you can do in libpq is multiple commands in a
> PQexec string.

thanks for explanation.
do you think it's worth extending the libpq api to allow two or
more in-flight commands?

YAMAMOTO Takashi

>
>             regards, tom lane

yamt@mwd.biglobe.ne.jp (YAMAMOTO Takashi) writes:
> do you think it's worth extending the libpq api to allow two or
> more in-flight commands?

That wouldn't be so much an "extension" as a "total redesign, breaking
most existing code".

            regards, tom lane