OS buffer cache with DIO on Linux

From: Vitalis Jerome <vitalisman_at_gmail.com>
Date: Mon, 19 May 2008 15:25:54 +0200
Message-ID: <68b128550805190625x49f80f68k522c10c3aefc72c9@mail.gmail.com>

Hi all,

On RHEL4, RAC 10g+OCFS2 and filesystemio_options=setall, I've checked that physical reads still increase the "cached" column of "free" output, i.e. reading 1GB of data results in 1GB for the "cached" value.

Since it is of concern for such direct I/O, I've asked the Oracle support about that and their tentative explanation is that the shared memory (SGA) is included in this "cached" value on RHEL4. Any thought about that?

FYI this 32-bit system is not configured with HugePages nor ramfs or shmfs for the SGA. It is a "standard" RHEL4 installation regarding memory allocation.


Received on Mon May 19 2008 - 08:25:54 CDT

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