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Re: exclusive locking on SELECT ?

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: James Neff <jneff(at)tethyshealth(dot)com>
Cc: pgsql-jdbc(at)postgresql(dot)org
Subject: Re: exclusive locking on SELECT ?
Date: 2007-01-11 23:17:09
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-jdbc
On 11-Jan-07, at 4:47 PM, James Neff wrote:

> Greetings,
> I have 3 clients trying to do a select on the same table (different  
> rows).  pgAdmin III Server Status shows the queries and has as mode  
> "Exclusive Lock" for all three.
Are you doing select for update ? If so why so many rows ?

> After a long while (10 minutes maybe?)  things eventually get  
> unstuck and everything is alright.
> These clients are selecting 2000 rows from the database.  My  
> suspicion is the database servers IO is a bottleneck (running SATA  
> drives, not SCSI).  Would fetching less number of rows at a time be  
> better?  How can I find out what the best number of rows to fetch  
> at a time are?
> Is this a deadlock situation?

> How would I go about diagnosing this situation, and how do I fix it?

Have you tuned the server ?
> I'm just using the postgresql-8.2-504.jdbc2.jar on all three clients.
> I'm also researching and trying to implement the pooling suggested  
> before (trying DBCP first).  If that will fix this problem then  
> just disregard this.
> Thanks in advance,
> James
> ---------------------------(end of  
> broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings

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