[pgpool-general: 2387] Re: Error when use pgpool2 with JDBC

[Denis Thomas]

Hello,

2014/1/8 Lachezar Dobrev <l.dobrev at gmail.com>

>
>   Did you try the 3.3.2 version without protocolVersion=2?
>
>
Yes, and I get same exception than previously.



>   This is something you should care about: when using a transaction
> all queries are sent to the master node. This is needed in order to
> preserve data integrity and isolation. If you want to use the slaves
> for read-only queries you must not do so in a transaction.
>   For Springframwork I found out, that for read-only methods one
> should use @Transactional(propagation = Propagation.SUPPORTS, readOnly
> = true). This way Springframework creates the necessary infrastructure
> objects (Hibernate or JPA session) and will poll a connection to the
> database, but does not actually start a database transaction, which
> allows queries to go to a slave. This is a result of me talking to the
> Springframework guys a while back when we were trying Slony-I. I was
> advised to use this transactional demarcation to make use of read-only
> slaves.
>
>   Please anyone feel free to correct me if you believe any of the
> above is wrong.
>
>   Apparently when you use protocol version 2 the JDBC Driver uses a
> transaction (BEGIN; ... COMMIT) to execute the SET which *probably*
> makes it run on the master server only. I am not sure if this is a
> good thing. At best this seems to hide the problem, which might become
> apparent later.
>
>
Thanks for these details. Tatsuo Ishii said that protocol version 2 does
not support load balancing. So, I will have to give up it if I will must
use this version.


>   I currently have no test-bed with a running pgpool, but maybe you
> could create a simple test case: open a JDBC connection (no polling,
> no protocol specified, straight JDBC) to the pgpool, and observe the
> log files on both back-ends. Tatsuo Ishii noted, that the pgpool
> status shows that both back-ends behave differently when the SET is
> executed. There might be something there.
>

The two servers are configured with the same parameters, except fot
replication of course, and wal archiving, not activated on slave. Is it
possible that the problem come from ?

Denis
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