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Re: disabling seq scans

From: "Marcus Andree S(dot) Magalhaes" <marcus(dot)magalhaes(at)vlinfo(dot)com(dot)br>
To: <shannyconsulting(at)earthlink(dot)net>
Cc: <marcus(dot)magalhaes(at)vlinfo(dot)com(dot)br>, <pgsql-jdbc(at)postgresql(dot)org>
Subject: Re: disabling seq scans
Date: 2004-04-01 21:12:08
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-jdbc
Yes, that is what I thought 1st...
But, since we're using pooled connections, we must be extra
careful and ensure all connections have the enable_seqscan
reset to its default.
So, the main question is:

Do the pooling system resets the "enable_seqscan" variable
when the connections are delivered to the clients or we
*must* do it ourselves?

Another issue: when enable_seqscan is false, I found that
the sequential scanning is performed normally (as in
"select count (*) from <table>") but have them any performance

Last one... This time, specifically to the java side: what
do you think about adding new methods, say, setEnableSeqScan(boolean)
and getEnableSeqScan() to our (by our I mean
postgres) drivers?

> I do the following in several reports I run.....
> statement = m_conn.createStatement();
> statement.executeUpdate( "set enable_seqscan = false" );
> do your thing....
> statement.executeUpdate( "set enable_seqscan = true" );
> --sean
> Marcus Andree S. Magalhaes wrote:
>>Hi, guys,
>>We're experiencing a little problem with one of our queries.
>>It isn't using an index specially created for it. When we
>>disable seq scans with psql, we can ensure the query finishes
>>much faster than without using index, as it should be.
>>So, whats the best procedure in this case, but when have a
>>JDBC based client? Do we mess around with planner
>>settings even when all other queries are using the best
>>index for them?
>>Is it safe (but some may find ugly) to issue a command to
>>disable seq scanning from the java side?
>>Since we're using the pooled connection classes that comes
>>with the JDBC3 driver, once a connection is got from the pool,
>>do we need to explicitly set seq scanning to true? This is
>>assuming the later option is the more recommended one...
>>---------------------------(end of
>> broadcast)--------------------------- TIP 8: explain analyze is your
>> friend
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if
> your
>       joining column's datatypes do not match

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