[pgpool-general: 5672] Re: How to extend load balancing in pgpool II
ishii at sraoss.co.jp
Wed Aug 2 08:54:04 JST 2017
> I would like to know whether it is possible to configure load balancing
> module in pgpool II so that it will be possible to redirect requests on the
> basis of tables (in the sql query) as well. For e.g., configurations like
> database_redirect_preference_list and app_name_redirect_preference_list
> gives us the granularity to redirect on the basis of database / clients.
> I'm looking for something like
> table_name_redirect_preference_list =
> I couldn't find any such configurations
That is not supported in Pgpool-II.
> - Is it possible to write some
> extensions (custom code to do the stuff mentioned above ) and attach it to
> pgpool II
> or will it be required to branch and add that piece of code to
> pgpool source and do a build / install ?
Yes. BTW I think you should decide what to do if table1 and table2 are
used in a SELECT.
> Reason : - I have set up a postgres cluster with SR (Streaming
> Replication). Due to inherent design, things are asynchronous and there
> will be a read miss if a recently inserted row in master was read from the
> slave. I went through the configuration sr_check_period and
> delay_threshold. What will happen to requests (insert row; read same row;)
> which was done under 1 second (lowest possible value for sr_check_period).
> I do not want to opt for sync replication due to performance reasons and
> also due to the fact that majority of the queries are "reads".
> I'm aware of tables with heavy writes - Hence such a configuration / module
> (if available in runtime - even better) will help me to circumvent the
> problem. Of course, I'm pretty much new to pgpool II - Please correct me
> I've got it completely wrong.
A workaround for the problem is using an SQL comment.
If "allow_sql_comments" is off,
/*a comment*/select * from table1;
will be always redirected to primary (inside /* and */ is an arbitrary
string). Also you can use:
pgpool set allow_sql_comments to off;
to set the configuration variable temporarily.
SRA OSS, Inc. Japan
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