Re: Oracle creates multiple shared memory segments despite SGA < SHMMAX
From: <johnbhurley_at_sbcglobal.net>
Date: Fri, 6 Mar 2009 03:42:14 -0800 (PST)
Message-ID: <b8a1fc27-7a29-41ea-a639-10e690e3e2d9_at_r29g2000vbp.googlegroups.com>
On Mar 5, 5:15 pm, ca111..._at_gmail.com wrote:
> This is new installation of 10.2.0.4 on HP-UX 11.23 Itanium.
> HP-UX kernel parameter SHMMAX is 10G,
> Oracle parameter SGA_MAX_SIZE set to 8G.
>
> On startup Oracle creates 4 shared memory segments, size in bytes:
> 4064346112
> 4076863488
> 488710144
> 20480
>
> Any idea why?
>
> Yes I know that it *should* run OK with multiple shared memory
> segments,
> and I am aware that it is normal to create segments with different
> size
> (Metalink Note 15566.1). Still I would prefer to have one segment, not
> 4.
>
> There is only one instance on this server, there is no other software
> that uses IPC (Tuxedo, etc), Oracle started immediatelly after server
> reboot.
>
> The only kernel parameter set to 4G is MAXDSIZ_64BIT. As far as I
> understand
> it shouldn't affect sizing of shared memory segments.
Date: Fri, 6 Mar 2009 03:42:14 -0800 (PST)
Message-ID: <b8a1fc27-7a29-41ea-a639-10e690e3e2d9_at_r29g2000vbp.googlegroups.com>
On Mar 5, 5:15 pm, ca111..._at_gmail.com wrote:
> This is new installation of 10.2.0.4 on HP-UX 11.23 Itanium.
> HP-UX kernel parameter SHMMAX is 10G,
> Oracle parameter SGA_MAX_SIZE set to 8G.
>
> On startup Oracle creates 4 shared memory segments, size in bytes:
> 4064346112
> 4076863488
> 488710144
> 20480
>
> Any idea why?
>
> Yes I know that it *should* run OK with multiple shared memory
> segments,
> and I am aware that it is normal to create segments with different
> size
> (Metalink Note 15566.1). Still I would prefer to have one segment, not
> 4.
>
> There is only one instance on this server, there is no other software
> that uses IPC (Tuxedo, etc), Oracle started immediatelly after server
> reboot.
>
> The only kernel parameter set to 4G is MAXDSIZ_64BIT. As far as I
> understand
> it shouldn't affect sizing of shared memory segments.
I think I remember something similar from Kevin Claussens ( sp? ) blog. Probably not remembering correctly but thought that the postings were on linux but that at some point oracle code internally can allocate it in separate chunks.
Personally I am still paranoid about oracle re-sizing SGA components as their have been more than a few bugs in that whole area.
Anyway see if you can dig out what Kevin wrote up ( might have also been on So What ) which may or may not be relevant. Push oracle support to see if you can get some details out of them.
I don't see anything like that on my hpux 11.23 machines but they are not Itanium and also not using the dynamic size changing stuff for SGA. Received on Fri Mar 06 2009 - 05:42:14 CST