RE: About O/S file system cache in any Linux OS: RHEL/OEL

From: William Muriithi <>
Date: Sun, 1 Nov 2009 20:59:45 -0600
Message-ID: <>


By default you dont have to do any special configuration to use Linux file system buffer cache, Linux tries to cache everything.

Correct, by default, caching is enabled. However if you still want to change it, look at this two parameters in the file /etc/sysctl.conf. You can see all the parameters by typing /sbin/sysctl -a on the terminal

vm.overcommit_ratio = 50
vm.overcommit_memory = 0

Worth looking at this article

But filesystem buffer read is not very good idea, if you are using Linux 32 bit it is ok but if you are using 64 bit you should give more memory to db_cache_size and cache in Oracle's own cache and avoid double buffering (file system buffer and oracle data block buffer).

On top of double caching as explained above, do not be too aggressive with overcommit. If you are running a program that is misbehaving, it can lead to the kernel rudely killing oracle. This would happen after the run away process has exhausted all resources and the kernel has to do something for the system to be usable again.

If you have less that 4GB RAM, 32 and 64 kernel should just about behave the same way. However, with more than 4GB, the oracle can still get killed if you run out of the lower memory. It wouldn't matter if there exist tonnes of unused upper memory. The solution is to configure the kernel to use the higher memory for caching. Look at the sysctl if that happen to be your case.


On Sun, Nov 1, 2009 at 6:48 AM, sundar mahadevan <<>> wrote: Hi Gurus,
I was reading through metalink to know more about db file scattered read on Note 223117.1 which further provided link to Note 34558.1

One of the solutions to decreasing wait times was using O/S file system cache : "It can help to place files which incur frequent table/index scans on disks which have are buffered by an O/S file system cache. Often this will allow some of Oracles read requests to be satisfied from the OS cache rather than from a real disk IO."

I know about the table CACHE feature that can be used to help cache tables that are frequently scanned within oracle.

But how does one setup O/S file system cache. I googled about O/S file system cache but not with much help. Any links or thoughts are much appreciated. Thanks in advance.

-- Received on Sun Nov 01 2009 - 20:59:45 CST

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