Originally posted by: SystemAdmin

We have a Oracle10g RAC ( 8 node) using ASM as storage on AIX 5.3L. we have 64GB memory, out of which 24 GB allocated to Oracle SGA. We observe, almost 50+% of total memory being used in File system Cache (reported by svmon -G+nmon ).

Since ASM (non AIX filesystem) being used here, we don't need to cache any data.. Do we? Using 50+% of total memory for filesystem where no data (except root fileystem & Oracle Binaries ) seems to be a waste. Isn’t it? .

What’s the recommended way to reduce memory used by File system cache? Is it possible to reduce maxclient & maxperm ( we have lru_repage = 0 and maxclient & perm parameters at their defaults ) in this scenario? What are the implications of having maxperm/maxclient reduced?

Thanks in advance for your help.
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Originally posted by: esv

Are you using JFS2 filesystems? if so, you could use CIO option but you need to setup Oracle to work with the CIO (concurrent I/O) also, for CIO filesystems, you need to umount and re-mount the filetsystems.

You have to make sure your cache hit ratio is high otherwise your application will suffer.

best regards,
esv.
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Originally posted by: SystemAdmin

Enrique,

Thanks for your reply.. Only JFS2 file systems we have is root (for AIX binaries & paging/swap space ) and other is for oracle binaries and I guess, none of them can be made to use CIO/DIO... Right?

All the data is stored on Oracle ASM storage ( i.e. raw volumes ) which does not use Filesystem cache.. so looking for ways to reduce the filesystem cache size...

Thanks
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Originally posted by: orphy

Go through this wp, specifically pages 12-13 for you.

http://www-03.ibm.com/support/techdocs/atsmastr.nsf/5cb5ed706d254a8186256c71006d2e0a/f939ff19b6430df7862570e5005027dc/$FILE/10gRAC_ASM.pdf
Orphy
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Originally posted by: SystemAdmin

Here are the lines from this doc..

With AIX5.2ML4 and above, we instead typically use the following values:

• lru_file_repage=0
• minperm% = 5
• maxclient% = 80
• maxperm% = 80

My question is, can maxclient and maxclient be lower value than 80%? What are the implications of doing that?

With this setting, AIX using 75% of Total memory for FS cache..in our case 64*.75= 48GB.. So, the question is , Does AIX needs this much memory when there is no data on File system? What happens when sudden surge of demand for process memory ? LRUD needs to free-up these pages from FS memory and that incure some cost. Doesn't it?
Hope I'm clear now...

TIA.
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Originally posted by: MarkTaylor

If there are no file pages to cache, then no file pages will get cached

maxperm and maxclient are only high water marks used by VMM to determine allowable memory for file system cache usage. if you dont access any files, then you wont get any file pages cached.


In what circumstances woul this actually happen. You have already stated that your SGA is 24GB, so Oracle wont just go and grab another 24GB ?? and also, if you dont cache file pages as you dont have any to cache, then there are still going to be pages left on the freelist.

vmstat -v ## will show numperm% and numclient%

Rgds
Mark Taylor
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Originally posted by: SystemAdmin

1) there is sudden burst of connections.. This would need process memory...or Parallel Query slaves being spwaned etc etc..
Also I'm still scratching my head as to what's using the File system cache.. All I have is AIX (root volumes ) & Oracle binaries and paging space... What command would show me the contents of filesystem cache?
Thanks again..
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Originally posted by: SystemAdmin

Any more feed back ??
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