[pgpool-general: 541] Re: load balancing seems to be bottlenecked by performance of master

[Tatsuo Ishii]

> 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.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp