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тАО03-16-2006 03:04 AM
тАО03-16-2006 03:04 AM
We have some rx4640's with 24 Gig each of memory and two rx2620's with 8 Gig each of memory. These servers run oracle but are still configured such that the dbc_max_pct and dbc_min_pct are at 50 and 5 percent respectively. I understand that these values are high. One of the HP tuning manuals recommends 30 and 20 percent respectivly. From what I have read on this forum, it is not the percent value but the absolute value that should be considered in adjusting these parameters. First, is this true? Second, can anyone give me an absolute value recommendation for these two parameters. I will not poison the returns by listing the most commonly recommended absolute values mentioned on this forum.
Thanks,
Darrell Tschakert
Solved! Go to Solution.
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тАО03-16-2006 03:11 AM
тАО03-16-2006 03:11 AM
Re: dbc_max_pct settings
Pete
Pete
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тАО03-16-2006 03:13 AM
тАО03-16-2006 03:13 AM
SolutionNo - 20 & 30% are probably *still* too high.
Set the % such that you allocate a max of around 800MB - so that would be around 4% on the 24GB system & 10% on the 8GB system.
Your minimum can be probably 2%.
HTH,
Jeff
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тАО03-16-2006 03:13 AM
тАО03-16-2006 03:13 AM
Re: dbc_max_pct settings
You are going to find that the "sweet spot" lies somewhere in the 800-1600MB range on the newer versions of HP-UX. Very seldom, do cache sizes above 1600MB improve performance. If you are running Oracle, especially with raw devices, then you should make the SGA's large and reduce the UNIX buffer cache to ~800MB.
Eventhough the newer versions of HP-UX are good at ramping down the dynamic buffer cache, I still prefer to run static buffer caches by setting bufpages to a non-zero value (bufpages=409600 for 1600MB). This means that the buffer cache stays near the "sweet spot" even if you add much more meory to these boxes.
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тАО03-16-2006 03:18 AM
тАО03-16-2006 03:18 AM
Re: dbc_max_pct settings
Since you have alot of memory talking in % make s not much sence...
The issues you have with to much buffers is when it comes to sync... it can take quite some time if very large and there is alotto write down to disks, so I suppose it depends on your disks performance (FC ? on a SAN cache centric?...) but to be safe try to stay within a limit a 1 GB, I wouldnt give more than 500 MB to system with 8GB RAM...
All the best
Victor
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тАО03-16-2006 03:39 AM
тАО03-16-2006 03:39 AM
Re: dbc_max_pct settings
Isn't the size of this buffer cache as important as the options you used to mount your database ?
What I mean is that in performance course we speak about the well known "double buffers, so isn't it much intersting to have for exemple a buffer cache ,as defined like Victor says or up to 800 Mo according to Clay, but bypassing this buffer cache for oracle datafiles than having a big one of 1600Mo and a high level access on it and impacting the others FS using it ?
Any advise ?
Regards
Pat
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тАО03-16-2006 03:47 AM
тАО03-16-2006 03:47 AM
Re: dbc_max_pct settings
At 11.23, you even have the Cluster File System (CFS) so that fully cooked files can be used with OracleRAC.
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тАО03-16-2006 03:59 AM
тАО03-16-2006 03:59 AM
Re: dbc_max_pct settings
This famous performance course was provided by HP education on HP11i, so I'm also surprised but it's a very good think to have you explanation.
Thanks a lot.
Pat
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тАО03-16-2006 04:09 AM
тАО03-16-2006 04:09 AM
Re: dbc_max_pct settings
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тАО03-16-2006 04:55 AM
тАО03-16-2006 04:55 AM
Re: dbc_max_pct settings
Darrell Tschakert