[pgpool-general: 543] Re: load balancing seems to be bottlenecked by performance of master

Tatsuo Ishii ishii at postgresql.org
Tue May 29 10:52:54 JST 2012

> On 05/28/2012 06:43 PM, Tatsuo Ishii wrote:
>>> On 05/28/2012 05:55 PM, Tatsuo Ishii wrote:
>>>>> On Mon, May 28, 2012 at 5:23 PM, Tatsuo Ishii<ishii at postgresql.org>
>>>>> wrote:
>>>>>>> On Mon, May 28, 2012 at 3:54 PM, Tatsuo Ishii<ishii at sraoss.co.jp>
>>>>>>> wrote:
>>>>>>>>> What are the reasons for analysing system catalogs on primary server?
>>>>>>>> For example, if a table is a temporary one or not.
>>>>>>> Yes, but as I noted, I don't use temp tables at all.  If this is the
>>>>>>> primary justification, then its not doing me any good, and causing
>>>>>>> unnecessary negative performance impact.
>>>>>> But how does pgpool know that you are not going to use temporary
>>>>>> tables beforehand?
>>>>> Provide a new pgpool.conf option that tells it to ignore them (with
>>>>> the assumption that they do not exist).
>>>>>>> I understand if this isn't something you can fix right now, but I'm
>>>>>>> not even getting the impression that you consider this to be a design
>>>>>>> flaw.  A high write volume on the master should never impact the
>>>>>>> response time of any standby/slave with a read query.  This literally
>>>>>>> means that pgpool doesn't scale well in write heavy environments.
>>>>>> That's why I asked you any idea to solve the problem.
>>>>> I guess I don't understand why pgpool needs to look up the system
>>>>> catalogs on the write server.   Shouldn't they be identical on all
>>>>> servers?
>>>> You cannot assume that because streaming replication or slony are
>>>> async replication.
>>>> Also remember that temp tables can only be used on primary.
>>> could you create a list of valid tables at startup and periodically
>>> poll for new tables? if it's an unlogged table you'll know, and if
>>> it's a temp table (or a very new table) you just wouldn't allow it to
>>> be load balanced.
>> Interesting idea. However I am afraid you will not know if it's a temp
>> table or not until you query the system catalog.
> you wouldn't need to, if it's not in your list of "ok" tables it
> doesn't get load balanced. temp and unlogged tables would never be in
> the list. Worst case would be that a valid new table wouldn't be
> allowed to be load balanced until the list was refreshed.

Ok, so your idea is, any new table (regardless it's a regular, temp or
unlogged one) will not be load balanced if it's not in the predefined
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

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