[pgpool-general: 215] Re: Another question about num_init_children and max_pool

Erwan ebs at antelink.com
Mon Feb 6 17:04:51 JST 2012


thank you Tatsuo !

/Erwan

On 02/05/2012 01:12 AM, Tatsuo Ishii wrote:
>> I use a pgpool-II v3.0.5 compiled and installed by my self on a Debian
>> Squeeze.
>> I only use pgpool-II as a loadbalancer between 2 database nodes which
>> stay synchronized via an Hot Standby replication.
>> In my pgpool-II configuration one of this node has a really high
>> weight than the other (1000 against 1) to be the prior node to answer.
>>
>> Everything works well but I have a question about the pool of
>> connections.
>> In my pgpool-II configuration I have the following settings:
>> ...
>> num_init_children = 19
>> max_pool = 4
>> ...
>>
>> I set it like that because I believed there would be a maximum of 4x19
>> = 76 potential connections.
>> During a test I launched a lot of long queries... and I noted there
>> were only 19 connections at the same time and I have to wait for the
>> end of a previous queries to launch the next one...
>> All my connections came from the same host and used the same database
>> and user.
>> I also read in a previous mail on this mailing list
>> (http://www.mail-archive.com/pgpool-general@pgfoundry.org/msg03334.html)
>> it's normal it's only 19 active connections at a time.
>> But I don't really understand how I can reach 76 connections if I only
>> have 19 active at one time? And in this case, is the pool really
>> useful? I just would like there will be a maximum of 76 connections at
>> a time.
>> According to another mail
>> (http://www.sraoss.jp/pipermail/pgpool-general/2011-December/000070.html)
>> I will be tempted by setting up my pgpool-II as following:
>> ...
>> num_init_children = 76
>> max_pool = 1
>> ...
> num_init_children is max concurrent *active* connections to
> PostgreSQL. So, yes, you see only 19 connections is quite normal. The
> possibility of exceeding 19 is, you connect to pgpool with different
> user, database combination. Suppose you want to use different
> databasae A and B, you will have 19*2 = 38 connections at
> max. However, the max *active* connection to PostgreSQL is still
> 19. Rest of 19 is idle and are waiting for becoming active.
>
> So if you are sure that you have only 1 user, database combo,
>
>> num_init_children = 76
>> max_pool = 1
> this setting makes sense.
> --
> 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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