IDS Forum

RE: Significance of high Btree percentage?

Posted By: Brian Amstutz
Date: Tuesday, 6 October 2009, at 10:31 a.m.

In Response To: Re: Significance of high Btree percentage? (Art Kagel)

So if ours is mostly an OLTP system with a little bit of Data Warehousing
activity thrown in, then a BTree of say, 35%-45% (or lower) is probably
"OK", correct.?

As far as 'meaning' - is it correct to say, then, that this represents
(the percentage of) btree indexes that were loaded into the BUFFER and are
still sitting there?

Are these flushed during normal BUFFER recycling?

Is a high Btree% potentially not a good thing because that means there's
less BUFFER space for data?

If I see this continually staying high, what parameters do I need to be
looking at in order to bring it back down (i.e. #buffers, #lrus, ...)?

I saw a reference to an LRUAGE environment variable - would this be
something I need to explore using if Btree % is continually high?

Thanks!

Brian
Asbury Theological Seminary

>-----Original Message-----
>From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of Art
Kagel
>Sent: Monday, October 05, 2009 4:21 PM
>To: ids@iiug.org
>Subject: Re: Significance of high Btree percentage? [17345]
>
>"normal" is going to depend on your access patterns. A typical OLTP
system
>will show less than 35% BTREE pages in the buffer cache, a Data Warehouse
>will typically show upwards of 65% BTREE pages, DSS somewhere in between.
>
>There were versions, early 7.31 releases, that ran into a bug that caused
>index pages to incorrectly dominate the cache (>90%) causing performance
>problems, however, 10.00 does not suffer from this bug.
>
>Art
>
>Art S. Kagel
>Oninit (www.oninit.com)
>IIUG Board of Directors (art@iiug.org)
>
>Disclaimer: Please keep in mind that my own opinions are my own opinions
and
>do not reflect on my employer, Oninit, the IIUG, nor any other
organization
>with which I am associated either explicitly or implicitly. 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 Mon, Oct 5, 2009 at 3:09 PM, Brian Amstutz <
>brian.amstutz@asburyseminary.edu> wrote:
>
>> HPUX 11vi2, 4x440MHz cpu, 8GB RAM, Informix 10.00.HC5=20
>>
>> So, what is the significance/meaning of a high Btree percentage (onstat
>> -P)?
>>
>> Often (but not always) ours is quite high which, from the little I've
>> read, is not a good thing. For example:
>>
>> onstat -P | tail -10
>>
>> Totals: 400000 223186 173344 3470 299
>>
>> Percentages:
>> Data 43.34
>> Btree 55.80
>> Other 0.87
>>
>> Is it OK/normal for it to fluctuate between a low and high percentage?
>> What settings should I be looking at to tune?
>>
>> Thanks!
>>
>> Brian Amstutz
>> Asbury Theological Seminary
>>
>>
>>
>>
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Messages In This Thread

• Significance of high Btree percentage?
  Brian Amstutz -- Monday, 5 October 2009, at 3:09 p.m.
  • Re: Significance of high Btree percentage?
    Art Kagel -- Monday, 5 October 2009, at 4:20 p.m.
    • RE: Significance of high Btree percentage?
      Brian Amstutz -- Tuesday, 6 October 2009, at 10:31 a.m.
      • Re: Significance of high Btree percentage?
        Art Kagel -- Tuesday, 6 October 2009, at 11:23 a.m.

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