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Re: Defragment questions ?

Posted By: Art Kagel
Date: Thursday, 25 April 2013, at 8:57 a.m.

In Response To: Re: Defragment questions ? (Franck THOMAS)

Alexandre's concern's about the effects of the IOs and the manual's notes
about buffer usage possibly affecting performance during peak loads are
valid. I took the question as applying to safety and lock contention
which, as you saw when you tested the deletes, updates, and inserts is not
an issue.

I do not know how many pages are used, no, and it is not configurable.

I'm here at the IIUG Conference in San Diego. There was a session on this
and one gotcha came out of it: Be careful not to interrupt the session
performing the defragment or to bounce the instance until it completes.
The official word is that this is safe, but some users have had problems
from long recovery after shutdown to a server crash after killing the
defragment session with onmode -z, so caviat emptor.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions
and do not reflect on my employer, Advanced DataTools, the IIUG, nor any
other organization with which I am associated either explicitly,
implicitly, or by inference. Neither do those opinions reflect those of
other individuals affiliated with any entity with which I am affiliated nor
those of the entities themselves.

On Thu, Apr 25, 2013 at 2:18 AM, Franck THOMAS
<franck.thomas@consult-ix.fr>wrote:

> Hi Art, Alexandre,
>
> Thank you for your answers.
>
> Art, you tell me that there is no risk with defragment feature in the
> environment production.
>
> In the article "Understand the Informix Server V11.7 defragmenter"
>
> (
> http://www.ibm.com/developerworks/data/library/techarticle/dm-1011informixdefragmenter/
> ),
> I read "The defragmenter uses the buffer pool for this movement in order
> to keep the data in sync with other uses. *If buffer pool usage is a
> concern, then running the defragmenter at a non-peak time is
> recommended.**"**
> *
> When do you think ?
> Another question : "The defragment moves a small number of pages at a
> time."
> Do you know how many pages (maximum) can be moved by the defragment ?
> This small number can be changed by us with a Informix parameter ?
>
> Alexandre, your tips of good pratice are interesting.
>
> I did some tests, I defragmented a table with 50 million of rows.
> During the defragment task, I run several queries : Delete 10 000 rows
> or Update 10 000 rows or Insert new 10 000 rows.
> No problem. All work.
> But, I was not in an environment production.
>
> Regards,
>
> Le 24/04/2013 15:33, Art Kagel a écrit :
> > The DEFRAGMENT feature is VERY light weight. It moves a small number of
> > pages at a time in a small transaction. There is no more impact on other
> > users than there would be if a user were updating a few dozen to a few
> > hundred rows in a single transaction.
> >
> > Art
> >
> > Art S. Kagel
> > Advanced DataTools (www.advancedatatools.com)
> > Blog: http://informix-myview.blogspot.com/
> >
> > Disclaimer: Please keep in mind that my own opinions are my own opinions
> > and do not reflect on my employer, Advanced DataTools, the IIUG, nor any
> > other organization with which I am associated either explicitly,
> > implicitly, or by inference. Neither do those opinions reflect those of
> > other individuals affiliated with any entity with which I am affiliated
> nor
> > those of the entities themselves.
> >
> > On Wed, Apr 24, 2013 at 7:59 AM, Franck THOMAS
> > <franck.thomas@consult-ix.fr>wrote:
> >
> >> Hi everybody,
> >>
> >> I read the technical documentation on defragment feature.
> >> I did several tests and all works well with the defragment.
> >> But, I would like to be sure :
> >> Do you know if there is a risk when we defragment a table or a
> >> partition when we have a peak of activity (by example : numberous
> >> transactional query to update, delete or insert into the table) ?
> >> In your experience, did you meet a problem when we run a defragment on a
> >> environment production ?
> >>
> >> Regards,
> >>
> >> --
> >> Franck Thomas
> >> ConsultiX
> >> franck.thomas@consult-ix.fr
> >> http://www.consult-ix.fr
> >> Téléphone : 33 (0) 1 39 12 18 00
> >> Mobile : 33 (0) 6 78 81 09 33
> >> Fax : 33 (0) 1 39 12 18 18
> >>
> >>
> >>
> >>
> >
>
> *******************************************************************************
> >> Forum Note: Use "Reply" to post a response in the discussion forum.
> >>
> >>
> > --001a11c20c9ae2c45d04db1b57c8
> >
> >
> >
>
> *******************************************************************************
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
> >
>
> --
> Franck Thomas
> ConsultiX
> franck.thomas@consult-ix.fr
> http://www.consult-ix.fr
> Téléphone : 33 (0) 1 39 12 18 00
> Mobile : 33 (0) 6 78 81 09 33
> Fax : 33 (0) 1 39 12 18 18
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

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Messages In This Thread

• Defragment questions ?
  Franck THOMAS -- Wednesday, 24 April 2013, at 7:59 a.m.
  • RE: Defragment questions ?
    Alexandre Marini -- Wednesday, 24 April 2013, at 8:21 a.m.
  • Re: Defragment questions ?
    Art Kagel -- Wednesday, 24 April 2013, at 9:33 a.m.
    • Re: Defragment questions ?
      Franck THOMAS -- Thursday, 25 April 2013, at 5:18 a.m.
      • Re: Defragment questions ?
        Art Kagel -- Thursday, 25 April 2013, at 8:57 a.m.

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