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тАО09-07-2009 12:56 AM
тАО09-07-2009 12:56 AM
Thank you and regards,
Tiziano.
Solved! Go to Solution.
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тАО09-07-2009 01:46 AM
тАО09-07-2009 01:46 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
Read Cache Hits 394 99.7 22226096 99.9 100.0
Write Cache Hits 20 50.0 786281 87.3
100% for reads and 50% for writes, now I'm at 100% memory allocation, my question is: tune down the max buffer cache or keep it like it is because if the user-sys procs require more memory it will be automatically deallocated?
Tiziano.
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тАО09-07-2009 04:10 AM
тАО09-07-2009 04:10 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
buffer cache does dynaically allocate between the dbc_min_pct and the dbc_max_pct in the kernel.
There is a huge performance penalty whenever the buffer cache changes so most folks set both numbers at a fixed figure that works for their server.
SEP
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
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тАО09-07-2009 04:41 AM
тАО09-07-2009 04:41 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
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тАО09-07-2009 04:47 AM
тАО09-07-2009 04:47 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
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тАО09-07-2009 05:34 AM
тАО09-07-2009 05:34 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
You mention of dbc_max_pct, and not filecache* implies that you are not on 11.31 yet, but you did not specify the exact version. This is important
The performance impact SEP refers to has been getting less important as HPUX has improved over time over the various releases.
On 11.31 you would pretty much no longer need to worry about it.
Now whether the you have to worry about 50% buffer cache can not be determined by looking at the buffer cache, but rather at the VM side where it is potential stealing from.
So you need to look a vmstat, and swapinfo or th glance components to see whether there is (excessive) page in and page out (some is ok).
Whether the cache is big enough can only be answerred if you understand the IO configuration. The purpose of the cache it to reduce the system IO requirements to a level that can be satisfied by the IO system.
If the system requires 10,000 pages per second, and there is 99% cache hit rate, then the IO subsystem needs to deliver 100 pages/sec which even a single disk can do. The cache is big enough or even oversized.
But if the box needs 1,000,000 pages per second then a 99% hit rate still leaves 10,000 real IO/sec and you'll either need a whopping serious IO system with several fibrechannel connections and 100+ disks behind that, or you need more cache still.
Whether the cache is big enough or too big can almost best be asked to the application users. Is the system 'behaving'? Are the end users happy with the performance?
I would like to encourage you to read up on some of this in the HP UX cookbook (Stephen Ciullo, & Doug Grumann).
Start with a search for reference to dbc_max_pct ... but do not stop there!
http://h21007.www2.hp.com/portal/download/files/unprot/devresource/Docs/TechPapers/UXPerfCookBook.pdf
Enjoy!
Hein.
HvdH Performance Consulting.
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тАО09-07-2009 06:35 AM
тАО09-07-2009 06:35 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
It's an 11i v2 on PA-RISC.
Ther's no significant page-in page-out activity and low physical IO on the discs, but all the memory is allocated. My question is: if I start a process _now_, will it allocate physical mem (deallocating buffer/cache) or will it be allocated in the swap area of the virtual mem space?
They are afraid that 100% memory allocation means no more physical mem for the user procs, but my knowledge was that buffercache is deallocated for sys/user procs mem.
I've attached some mem and VM stats.
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тАО09-07-2009 06:41 AM
тАО09-07-2009 06:41 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
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тАО09-08-2009 03:20 AM
тАО09-08-2009 03:20 AM
Re: About buffer cache allocation, really dynamic? dbc_max_pct dbc_min_pct
"They are afraid that 100% memory allocation means no more physical mem for the user procs, but my knowledge was that buffercache is deallocated for sys/user procs mem."
Thank you!
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тАО09-08-2009 03:33 AM
тАО09-08-2009 03:33 AM