[Pgpool-general] Basics of replication with pgpool-II - how does it work? compared to Slony? to Postgres log shipping?

[Ramon de Carvalho Valle]

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On 06/08/2010 10:03 PM, Tatsuo Ishii wrote:
>>> Yes, pgpool-II exactly works as you described. Plus, with write query
>>> pgpool-II start a transaction if it's not already started by user.
>>> The write order is first A then B (if A is the first one on
>>> pgpool.conf). Commit order is B then A.
>>>
>>>  If write query fails, pgpool-II aborts the transaction and start
>>> a  degenration, which will be seen as connection shutdown from
>>> PostgreSQL server by client. By reconnecting pgpool-II, client can use
>>> the healthy PostgreSQL.
>>>
>>> Please note that "fail" does not mean here a query error (for example,
>>> violation of constraints). Rather "fail" means network error or
>>> PostgreSQL server down or some such.
>> Would not it be a good behavior to degenerate the backends that return a
>> query error while the master do not?
> 
> Currently pgpool-II just detects number of affected raws by
> INSERT/UPDATE/DELETE and reports errors. Next verion of pgpool-II will
> allow user to choose degeneration in this case or not in addition to
> reporting errors.
So the only check I have in load balance mode is the health check? There
is no data integrity checks?

- -Ramon


> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
> 
>> I am concerned because I have an environment with seven backends in
>> load_balance_mode and it seems I can not be sure of the data integrity
>> of these backends in this mode.
>>
>> - -Ramon
>>
>>
>>>
>>>> If that's not how pgpool-II replication works, how does
>>>> it work?  I've looked at the manual but I still don't
>>>> understand.
>>>>
>>>> I'm familiar with replication with Postgres 8 log shipping
>>>> (warm standby),  Postgres 9 streaming replication
>>>> (hot standby), and Slony (hot standby).  How does
>>>> Pgpool-II replication work and how does it compare to
>>>> the Postgres/Slony replication?
>>>
>>> They are all log(physical or logical one) based asynchronous
>>> replication systems. Pgpool-II is a query based synchronous
>>> replication.  That's the big difference. In addition, those
>>> replication systems do not have any automatic failover/load balancing
>>> functionality while pgpool-II has.
>>> --
>>> Tatsuo Ishii
>>> SRA OSS, Inc. Japan
>>> English: http://www.sraoss.co.jp/index_en.php
>>> Japanese: http://www.sraoss.co.jp
>>> _______________________________________________
>>> Pgpool-general mailing list
>>> Pgpool-general at pgfoundry.org
>>> http://pgfoundry.org/mailman/listinfo/pgpool-general
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