Re: Trouble with FETCH_COUNT and combined queries in psql

Bonjour Daniel,

> When FETCH_COUNT is set, queries combined in a single request don't work
> as expected:
>
> \set FETCH_COUNT 10
> select pg_sleep(2) \; select 1;
>
> No result is displayed, the pg_sleep(2) is not run, and no error
> is shown. That's disconcerting.

Indeed.

> Does anyone have thoughts about how to fix this?

> ATM I don't see a plausible fix that does not involve the parser
> to store the information that it's a multiple-query command and pass
> it down somehow to is_select_command().

The lexer (not parser) is called by psql to know where the query stops
(i.e. waiting for ";"), so it could indeed know whether there are several
queries.

I added some stuff to extract embedded "\;" for pgbench "\cset", which has
been removed though, but it is easy to add back a detection of "\;", and
also to detect select. If the position of the last select is known, the
cursor can be declared in the right place, which would also solve the
problem.

> Or a more modern approach could be to give up on the cursor-based method
> in favor of PQsetSingleRowMode().

Hmmm. I'm not sure that row count is available under this mode? ISTM that
the FETCH_COUNT stuff should really batch fetching result by this amount.
I'm not sure of the 1 by 1 row approach.

--
Fabien.