IDS Forum

RE: How do it get writes form the lrus in V10

Posted By: Doug Conrey
Date: Wednesday, 3 May 2006, at 9:36 a.m.

In Response To: How do it get writes form the lrus in V10 (Bill Marshall)

> -----Original Message-----
> From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Bill
> Marshall
> Sent: Wednesday, May 03, 2006 7:21 AM
> To: ids@iiug.org
> Subject: How do it get writes form the lrus in V10 [6648]
>
>
> I have a new HP Intel 32 bit chip machine with 2 dual core processors
> and 8 Gb of memory.
>
> This machine runs one production database (Mostly OLTP) and a test
> database that is same thing but very low transactions
>
> When I run on stat -F I have 0 FG writes and 0 LRU writes and Chuunk
> writes of 15558 ( NOte this is after only approx 1 hour of production.
>
> I am running INFORMIX 10.00.UC3 workgroup edition.
>
> I am attaching the onconfig file and output of onstat -d
>
> I think I should be getting LRU writes. If you agree what parameters
> should I change to get them?
>
> ========================================
>
> # The following parameters are related to the buffer pool
> #BUFFERPOOL
>
default,buffers=800000,lrus=8,lru_min_dirty=20.000000,lru_max_dirty=25.0
00
> 000
> BUFFERPOOL
>
default,buffers=800000,lrus=8,lru_min_dirty=0.000010,lru_max_dirty=25.00
00
> 00
> #BUFFERPOOL
>
size=2K,buffers=800000,lrus=8,lru_min_dirty=20.000000,lru_max_dirty=25.0
00
> 000
> BUFFERPOOL
>
size=2K,buffers=800000,lrus=8,lru_min_dirty=0.000010,lru_max_dirty=10.00
00
> 00

The database will do LRU writes when the number of dirty buffers exceeds
a percentage set in the onconfig file. It will continue writing until
the percentage of dirty buffers reaches another percentage. The
percentages are set by the above parameters. Is this a Windows machine?
If so, you have two buffer pools, one 4K and one 2K. Each of these
tracks dirty buffers separately.
So you will start seeing LRU writes once your 4K buffer pool reaches 25%
dirty (200,000 4K buffers = 800MB) or once your 2K buffer pool reaches
10% dirty (80,000 2K buffers = 160MB). If this isn't a Windows or AIX
machine your default buffer pool size will be 2K, and I'm not certain
what these parameters will produce, since I believe you can only have
one buffer pool of a given size. 'onstat -R' will tell you.
In any case, you don't necessary want to see LRU writes unless you're
concerned about the length of your checkpoints. If you checkpoints are
short I don't think you really have a problem. Chunk writes are
generally more efficient. If your checkpoints are longer than you want,
you can increase LRU writing by decreasing the lru_max_dirty parameter.
On our production OLTP system (which has far fewer buffers) we have it
set to 1.25% to ensure that checkpoints are always very short (2 seconds
or less). You might also increase the lru_min_dirty (since it's
effectively at 0) so that the LRU writes don't last very long (since
they tend to be less efficient).
All of this comes from my knowledge of 9.4 and reading the docs for
10.0. I don't think it's changed too much.

DC

Messages In This Thread

• How do it get writes form the lrus in V10
  Bill Marshall -- Wednesday, 3 May 2006, at 9:21 a.m.
  • RE: How do it get writes form the lrus in V10
    Doug Conrey -- Wednesday, 3 May 2006, at 9:36 a.m.
  • Re: How do it get writes form the lrus in V10
    ART KAGEL, BLOOMBERG/ 731 LEXIN -- Wednesday, 3 May 2006, at 9:52 a.m.
  • Re: How do it get writes form the lrus in V10
    Nilesh Ozarkar -- Thursday, 4 May 2006, at 1:34 p.m.
    • Re: How do it get writes form the lrus in V10
      Bill Marshall -- Thursday, 4 May 2006, at 3:41 p.m.
      • Re: How do it get writes form the lrus in V10
        ART KAGEL, BLOOMBERG/ 731 LEXIN -- Thursday, 4 May 2006, at 4:28 p.m.

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