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From "Jeff Kilbride" <j...@kilbride.com>
Subject Re: AW: Java program interferring with Tomcat
Date Mon, 19 Nov 2001 21:41:27 GMT
Sure it does. Changing the transaction isolation level affects how data is
read from the database. TRANSACTION_READ_COMMITTED waits for a read lock
before reading data and ensures that the data being read is in a consistent
state. Lower isolation levels may allow data to be read that's
inconsistent -- data from a transaction that hasn't been committed, yet, and
therefore may be rolled back. However, that doesn't mean lower isolation
levels are "bad". They can relieve a lot of locking contention on the
database when used with queries that don't need perfectly consistent data.
It just depends on how critical the info you're pulling with this particular
query is.

For example:  are you tallying the number of visitors to your website or are
you doing financial transactions? With the former, reading "dirty" data may
not matter that much. With the latter, it may be critical that you have
consistent data. If your data's not that critical, you may get a lot of
benefit from lowering your transaction isolation level.

Thanks,
--jeff

----- Original Message -----
From: "David Frankson" <dfrankson@qwest.net>
To: "Tomcat Users List" <tomcat-user@jakarta.apache.org>
Sent: Monday, November 19, 2001 11:42 AM
Subject: Re: AW: Java program interferring with Tomcat


> > Not with SQL Server.  If thread A has a write lock on a table, thread b
> will
> > wait until the write is completed before reading.  If thread A is in a
> > transaction that is long running then a perfectly funcitoning
application
> > can seem to hang.  Its also possible that some form of infinite loop or
> > deadlock in thread A could cause it to never release the transaction,
> making
> > you either kill the application or use Enterprise Manager to kill the
> lock.
>
> Does changing the transaction isolation level affect things?  The tomcat
> application is a high traffic transactional system, and the commandline
app
> is a read-only data export tool that fires off twice a day.  Both are set
to
> TRANSACTION_READ_COMMITTED.
>
> Dave
>
>
>
>
> --
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