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IDS Forum

RE: need quick way to find whom is causing Blo....

Posted By: John Adamski
Date: Tuesday, 5 March 2013, at 9:15 a.m.

In Response To: Re: need quick way to find whom is causing Blocked (John Miller iii)

Thanks for the information,

I have LTXHWM set to 50 and LTXEHWM set to 60, sounds like I need to increase the difference.

The cause seems to be a developer added a new field to a large table that should have been defaulted to not null, when a cleanup process ran it found a large number of nulls in the field and tried to change them to blank.

I think I need to get a script setup to help identify who is causing these long transactions. Thanks everyone for your input.

John

-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of John Miller iii
Sent: Monday, March 04, 2013 12:19 PM
To: ids@iiug.org
Subject: Re: need quick way to find whom is causing Blo.... [29678]

Just a few points here.

Killing a session who is rolling back a long transaction will not help.
The servers undo daemon will assume the rollback for this session.

I believe what you want to look at is the difference between these two parameters. The first parameter LTXHWM will automatically force the session to start a rollback and NO other users will be effected by this one persons rollback. LTXEHWM (the parameter with the "E") is the threshold which provides EXCLUSIVE access to the logical logs and block all users attempting to write data. If you encounter this blockage my suggestion would be to increase the difference between this to values. By default hey come set at 70% and 80%. My suggestion would be to drop LTXHWM to 50%, What this means is any transaction which consume more than 50% of the logical logs will be forced to rollback and if it consume up to 80% of the logical logs it will stop others from writing to the logical logs and provide this transaction with exclusive resources.

# LTXHWM - The percentage of the logical logs that can be # filled before a transaction is determined to be a # long transaction and is rolled back # LTXEHWM - The percentage of the logical logs that have been # filled before the server suspends all other # transactions so that the long transaction being # rolled back has exclusive use of the logs

The other solution would be to utilize dynamic logs, which causes the logical logs to grow upon hitting a long transaction.

My last point would be to let you know that onstat -x has been enhanced to provide an estimation of how long it will take to rollback transactions. The column in onstat -x is called "rb_time".

If you want to look at this information programmatically look at the table called sysmaster:systxptab

John F. Miller III
STSM, Lead Architect
miller3@us.ibm.com
503-747-1366
IBM Informix Dynamic Server (IDS)

ids-bounces@iiug.org wrote on 03/04/2013 08:09:28 AM:

> From: "John Adamski" <adamski@graceland.edu>
> To: ids@iiug.org,
> Date: 03/04/2013 08:21 AM
> Subject: need quick way to find whom is causing Blocked.... [29670]
> Sent by: ids-bounces@iiug.org
>
> OS: HPUX 11.31 (11iv3) on BL870x IA server
> IDS: 11.70.FC4
>
> Friday afternoon we had a Blocked:LONGTX that locked up the database
> for
a
> while. I was informed while in a meeting that the "database is
> down"about
40
> minutes after the Blocked:LONGTX started.
>
> It took me a way too much time to find the session that had the block
> and
to
> kill that session; I was wonder what would have been the quickest way
> to
find
> who had the block that was preventing the rollback. As I'm sure I
> chose a less than speedy way to do find it.
>
> John Adamski, Sr. Network Specialist
> Graceland University, 1 University Place, Lamoni, IA 50140
> adamski@graceland.edu
>
>
>

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>

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