IDS Forum

Re: use of dbspaces?

Posted By: Art Kagel
Date: Thursday, 18 August 2016, at 1:51 p.m.

In Response To: use of dbspaces? (DAVID GROVE)

David:

A couple of points:

1. Cache hit percentages don't tell you the percentage of your data in

memory, but how efficient that data is once it gets into memory. If you

read 1000 pages into memory and reread one of those pages 200,000 times

during which time you have read an additional 999 pages overwriting all by

that one busy page, your read cache percentage is still 99%! similarly for

writes. Look to your BTR and/or BTR3 to tell you how well you are keeping

data in memory.

2. Disk layout can even matter with SSDs. Even SSDs have a maximum

number of IOs they can handle even if that is much higher than for

spindles. (BTW - I hope those SSD drives are not 10 years old ;-( - the

reliable life of SSDs sold today is only about 5 years.)

3. Don't discount the channels between the server and the disk array and

its capacity to funnel all that data.

4. If you make things REALLY simple, ie create a single huge dbspace

from a single huge chunk, then Informix is limited as to the parallelism it

can use to read data from and write data to storage. So you may not be

getting the full IO capacity of the drives if you did that.

Art

Art S. Kagel, President and Principal Consultant
ASK Database Management
www.askdbmgt.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 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, Aug 18, 2016 at 1:15 PM, DAVID GROVE <david.grove@alaska.gov> wrote:

> Gurus:
>
> If the entire database is cached in the bufferpool, does it matter how the
> database tables and indices might be physically deployed in dbspaces?
>
> I typically observe read cache hit rate to be 99.99% and write rate to be
> 98%.
>
> The database layout hasn't been modified for over 10 years, and I wonder
> if I
> should even care about taking a fresh look at allocation of tables,
> indices,
> etc. But, if the whole disk space management thing is about IO performance,
> and all my data objects are cached all the time, and there are no
> checkpoint
> issues or foreground writes, then maybe I can use my time better with other
> concerns. (BTW, all dbspaces and blobspaces are raw, and on mirrored SSDs.)
>
> Regards,
>
> DG
>
>
> ************************************************************
> *******************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

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Messages In This Thread

• use of dbspaces?
  DAVID GROVE -- Thursday, 18 August 2016, at 1:15 p.m.
  • Re: use of dbspaces?
    Fernando Nunes -- Thursday, 18 August 2016, at 1:29 p.m.
  • RE: use of dbspaces?
    Andrew Ford -- Thursday, 18 August 2016, at 1:32 p.m.
  • Re: use of dbspaces?
    Spokey Wheeler -- Thursday, 18 August 2016, at 1:46 p.m.
  • Re: use of dbspaces?
    Art Kagel -- Thursday, 18 August 2016, at 1:51 p.m.
  • Re: use of dbspaces?
    DAVID GROVE -- Thursday, 18 August 2016, at 2:33 p.m.
    • Re: use of dbspaces?
      DAVID GROVE -- Thursday, 18 August 2016, at 2:37 p.m.
      • Re: use of dbspaces?
        Art Kagel -- Thursday, 18 August 2016, at 2:54 p.m.
    • Re: use of dbspaces?
      Art Kagel -- Thursday, 18 August 2016, at 2:53 p.m.
    • Re: use of dbspaces?
      Fernando Nunes -- Friday, 19 August 2016, at 5:42 a.m.
  • Re: use of dbspaces?
    BENJAMIN THOMPSON -- Thursday, 25 August 2016, at 12:48 p.m.

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