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Re: Odd behaviour with redundant CREATE statement

From: Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>
To: Dave Crooke <dcrooke(at)gmail(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Odd behaviour with redundant CREATE statement
Date: 2010-09-27 19:27:53
Message-ID: AANLkTi=Og2L5EW12V9JbDcaGrBAiDsMTmLQ6QVS-OZXQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, Sep 27, 2010 at 8:50 PM, Dave Crooke <dcrooke(at)gmail(dot)com> wrote:

>
> Our Java application manages its own schema. Some of this is from
> Hibernate, but some is hand-crafted JDBC.
>
> By way of an upgrade path, we have a few places where we have added
> additional indexes to optimize performance, and so at startup time the
> application issues "CREATE INDEX ..." statements for these, expecting to
> catch the harmless exception "ERROR:  relation "date_index" already exists",
> as a simpler alternative to using the meta-data to check for it first.
>
> In general, this seems to work fine, but we have one installation where we
> observed one of these CREATE statements hanging up in the database, as if
> waiting for a lock, thus stalling the app startup


You can tell if it is really waiting by looking at 'select * from pg_locks',
and check the 'granted' column.



> it's PG 8.4.4 64-bit on RHEL 5, installed with the postgresql.org YUM
> repository.
>
> Stopping and restarting PG did not clear the issue. While this is going on,
> the database is otherwise responsive, e.g. to access with psql.
>

Also check if you have any prepared transactions waiting to be committed or
rolled back.

select * from pg_prepared_xacts


>
> Is this "expected failure" considered a dangerous practice in PGSQL and
> should we add checks?
>
> Does the hangup indicate a possible corruption problem with the DB?
>

Very unlikely.

Regards,
-- 
gurjeet.singh
@ EnterpriseDB - The Enterprise Postgres Company
http://www.EnterpriseDB.com

singh(dot)gurjeet(at){ gmail | yahoo }.com
Twitter/Skype: singh_gurjeet

Mail sent from my BlackLaptop device

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