Re: gc buffer busy from the same instance??
From: <stevedhoward_at_gmail.com>
Date: Sun, 10 May 2009 11:33:56 -0700 (PDT)
Message-ID: <871d1775-a9d1-432e-82d9-fc7a07d9a81d_at_o30g2000vbc.googlegroups.com>
On May 9, 12:44 pm, Mladen Gogala <mla..._at_bogus.email.com> wrote:
> On Fri, 08 May 2009 12:10:54 -0700, Steve Howard wrote:
> > When I select from gv$session, I see session x on instance 2 waiting on
> > "db file sequential read" for a given file and block number. I see
> > session y, also on instance 2, waiting on "gc buffer busy" for the same
> > file and block. These are the only two sessions going after this block.
>
> > I can understand (and would expect) this if session y was on instance 3,
> > or whatever. However, since both sessions are on the same instance, why
> > is this not either recorded as "read by other session" or "buffer busy
> > waits" event?
>
> If the block is owned by another instance (10.2 RAC has dynamic re-
> mastering, but it takes some time to for one instance to take ownership
> from another) then both sessions could be talking to the instance that
> owns the block. Usually that would result in the "2-way" waits, but since
> the requesting processes are both on the same instance, I am not sure. So,
> it's not completely out of this world but I do admit that the situation is
> unusual.
>
> --http://mgogala.freehostia.com
Date: Sun, 10 May 2009 11:33:56 -0700 (PDT)
Message-ID: <871d1775-a9d1-432e-82d9-fc7a07d9a81d_at_o30g2000vbc.googlegroups.com>
On May 9, 12:44 pm, Mladen Gogala <mla..._at_bogus.email.com> wrote:
> On Fri, 08 May 2009 12:10:54 -0700, Steve Howard wrote:
> > When I select from gv$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 re-
> mastering, 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.
>
> --http://mgogala.freehostia.com
Thanks, Mladen. Received on Sun May 10 2009 - 13:33:56 CDT