topic Re: Good Value For Buffer Cache in Operating System - HP-UX

Good Value For Buffer Cache

Basheer_2 — Thu, 12 Jan 2006 09:51:34 GMT

Hello Good morning

rp7420
11.23
dbc_min_pct = 5
dbc_max_pct = 7
Tot RAM = 24 GB
nproc = 4200
maxuprc = 4111
8 CPUs
Oracle11i ( ora 9.2.0)
No Other Apps.

Using this to calculate bufcache.
for the last week it is 1717 MB.

All docs say 300 to 400 MB is a Good one.
why is mine 1717 MB

all my other servers ( again only oracle) are above 500 MB and one is at 6500 MB.

Any Suggestions
Any Links for HP-UX ORACLE tuning, Parameters

Thanks

/usr/sbin/sysdef |grep bufpages|awk '{print $2*4096/(1024*1024)}'

Re: Good Value For Buffer Cache

Peter Godron — Thu, 12 Jan 2006 09:55:48 GMT

Basheer,
lots of info at:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=419867

Re: Good Value For Buffer Cache

Pete Randall — Thu, 12 Jan 2006 09:56:15 GMT

.05 x 24GB = 1.2GB, that's why.

Pete

Re: Good Value For Buffer Cache

James R. Ferguson — Thu, 12 Jan 2006 09:57:10 GMT

Hi Basheer:

You can use 'glance' to see the buffer cache in use let alone to monitor overall performance.

There is no "good" value other than what works best in your environment. I don't find the 5-7% range with 24GB a bad choice.

Regards!

...JRF...

Re: Good Value For Buffer Cache

baiju_3 — Thu, 12 Jan 2006 09:59:51 GMT

Hi Basheer,

Plz see the Unix Performance Cook Book attached .Its a good reference .

The values you have for a RAM of 24GB is a good one , I believe.

thx,
bl.

Re: Good Value For Buffer Cache

A. Clay Stephenson — Thu, 12 Jan 2006 10:02:03 GMT

Generally (and especially on systems with large amounts of memory) I find it better to set a static buffer size by setting bufpages to a non-zero value indicating the number of 4k pages.

On 11.11 and up, the buffer size "sweet spot" has moved up from the 400-800MB range to somewhere in the 1200-1600MB -- on most systems. Your values are not unreasonable but the nice thing about fixed buffer caches is that they remain fixed when the amount of memory changes --- and generally that means when more memory is added.

I would set the buffer cache on your box to about 1600MB (bufpages = 409600). The only real way to know where YOUR sweet spot is is to measure. In any event, given your amount of memory as long as you have your buffer cache somewhere near 1600MB the actual performance is only going to vary a little.

Re: Good Value For Buffer Cache

Victor BERRIDGE — Thu, 12 Jan 2006 10:29:06 GMT

Hi,

The issue is the sync time...
More you have buffers more time it will take to sync in ordinary usage (OLTP) the impact may not be noticable except for cursor not following when you are typing at the prompt for example
But when comes to batches it can give you some very nasty side effects....

So to answer you will have to try and see..
the values generally give here at ITRC are what we all found and agreed to be a good compromize and works for all of us.

I had once helped a bank 5 years ago which could not explain why their L2000 freezed for more than 15 minutes and had very bad performance every morning (early - end of night batches) and found out that the box and the default parameters but 8GB of RAM, I asked them to change min and dbc_max_pct to more convenient values and set swapmem_on to 0 and the system worked fine ever since...

All the best
Victor