[pgpool-hackers: 1595] Re: Proposal: connect to only neccessary DB nodes

[Muhammad Usama]

On Thu, May 26, 2016 at 3:59 AM, Tatsuo Ishii <ishii at postgresql.org> wrote:

> Long time ago I proposed this:
>
> > Here is a proposal for upcoming pgpool-II 3.5.
> >
> > The problem:
> > Currently pgpool-II connects to all the DB nodes registered in
> > pgpool.conf when client session initiates. However this may cause
> > certain inconvenience, especially using CREATE DATABASE command under
> > master/slave mode (including streaming replication mode). Suppose
> > there are two DB nodes, 0 is primary and 1 is standby. If a user
> > issues CREATE DATABASE and exits the session, then connects to the
> > newly created database, pgpool-II could fail to connect to node 1
> > since the new database might not be created on node 1 yet.
> >
> > Proposal:
> > In certain condition (I suppose load balancing is turned off), let
> > pgpool-II only connects to primary node only. This will avoid the
> > problem above since pgpool-II does not need to wait for newly created
> > database is ready once CREATE DATABASE is done.
>
> After thinking more, I think this problem not worth to attack since
> the use case (load balancing is off) is too narrow, and I would like
> to withdraw the proposal. Comments?
>

I totally agree with you on this, It's not worth an effort to solve this
very rare scenario.
Although I don't have any idea on how to do it, but I think instead we
should somehow try to
tackle the replication lag as a whole.  Which includes this above mentioned
scenario and also
the cases like when user does not starts the explicit transaction and the
writing query is immediately
followed by the select on the same table and it gets load balanced and
returns the old data.
But again, I don't have any idea on how to implement it or attack this
problem :-(

Best Regards
Muhammad Usama



>
> Best regards,
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
> _______________________________________________
> pgpool-hackers mailing list
> pgpool-hackers at pgpool.net
> http://www.pgpool.net/mailman/listinfo/pgpool-hackers
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.sraoss.jp/pipermail/pgpool-hackers/attachments/20160526/0751e74a/attachment.html>