Re: gc buffer busy from the same instance??

From: Mladen Gogala <>
Date: Sat, 9 May 2009 16:44:47 +0000 (UTC)
Message-ID: <gu4btv$a6t$>

On Fri, 08 May 2009 12:10:54 -0700, Steve Howard wrote:

> When I select from gv$session, I see session x on instance 2 waiting on
> "db file sequential read" for a given file and block number. I see
> session y, also on instance 2, waiting on "gc buffer busy" for the same
> file and block. These are the only two sessions going after this block.
> I can understand (and would expect) this if session y was on instance 3,
> or whatever. However, since both sessions are on the same instance, why
> is this not either recorded as "read by other session" or "buffer busy
> waits" event?

If the block is owned by another instance (10.2 RAC has dynamic remastering,  but it takes some time to for one instance to take ownership from another) then both sessions could be talking to the instance that owns the block. Usually that would result in the "2-way" waits, but since the requesting processes are both on the same instance, I am not sure. So, it's not completely out of this world but I do admit that the situation is unusual.

Received on Sat May 09 2009 - 11:44:47 CDT

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