| From: | "Daniel Verite" <daniel(at)manitou-mail(dot)org> |
|---|---|
| To: | "Alvaro Herrera" <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>,"Matthieu Garrigues" <matthieu(dot)garrigues(at)gmail(dot)com>,"Michael Paquier" <michael(at)paquier(dot)xyz>,"Dave Cramer" <davecramer(at)postgres(dot)rocks>,"PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>,"Craig Ringer" <craig(at)2ndquadrant(dot)com>,"Vaishnavi Prabakaran" <vaishnaviprabakaran(at)gmail(dot)com>,"Andres Freund" <andres(at)anarazel(dot)de>,"Michael Paquier" <michael(dot)paquier(at)gmail(dot)com>,"Claudio Freire" <klaussfreire(at)gmail(dot)com>,"Heikki Linnakangas" <heikki(dot)linnakangas(at)iki(dot)fi> |
| Subject: | Re: PATCH: Batch/pipelining support for libpq |
| Date: | 2020-11-14 14:42:50 |
| Message-ID: | b27523b8-6e41-44e8-8cc6-ea136316cdcd@manitou-mail.org |
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| Lists: | pgsql-hackers |
Alvaro Herrera wrote:
> I adapted the test code to our code style. I also removed the "timings"
> stuff; I think that's something better left to pgbench.
>
> (I haven't looked at Daniel's pgbench stuff yet, but I will do that
> next.)
The patch I posted in [1] was pretty simple, but at the time, query
results were always discarded. Now that pgbench can instantiate
variables from query results, a script can do:
select 1 as var \gset
select :var;
This kind of sequence wouldn't work in batch mode since it
sends queries before getting results of previous queries.
So maybe \gset should be rejected when inside a batch section.
Or alternatively pgbench should collect results before a variable is
reinjected into a query, thereby stalling the pipeline.
To do this only when necessary, it would have to track read-write
dependencies among variables, which seems overly complicated though.
[1]
https://www.postgresql.org/message-id/b4e34135-2bd9-4b8a-94ca-27d760da26d7@manitou-mail.org
Best regards,
--
Daniel Vérité
PostgreSQL-powered mailer: https://www.manitou-mail.org
Twitter: @DanielVerite
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