Re: Oracle creates multiple shared memory segments despite SGA < SHMMAX

snip

> Also see metalink 747486.1, 784919.1, 761065.1,7685006
>
> http://download.oracle.com/docs/cd/B19306_01/server.102/b15658/appb_h...
> says
> "When an Oracle Database instance starts, it creates memory segments
> by dividing the shared memory allocated for creating the Oracle Shared
> Global Area (SGA) by the value of the HP-UX shmmax kernel parameter.
> For example, if 64 GB of shared memory is allocated for a single
> Oracle instance and the value of the shmmax parameter is 1 GB, then
> Oracle Database creates 64 shared memory segments for that instance.
>
> Performance degradation can occur when an Oracle instance creates
> multiple shared memory segments. This is because each shared memory
> segment receives a unique protection key when Oracle Database creates
> the instance..."
>
> which seems at odds with what the OP is seeing... perhaps a support
> call would clear up what is happening.  My speculation is that MMAN
> had some problems which were hacked to fix, resulting in oddness like
> this.  Perhaps Sybrand is right, MMAN locking all those memory
> granules could mean a small number of users would set off swapping
> Real Soon Now, assuming the 10G implies physical memory.
>
> Or maybe they were trying to be nice about swap, and setting a big
> SHMMAX conflicts with that:  http://unix.derkeiler.com/Newsgroups/comp.sys.hp.hpux/2008-02/msg0007...
>
> jg
> --
> _at_home.com is bogus.http://www3.signonsandiego.com/stories/2009/mar/06/1b6kb215027-former...

Also take a look at the posts over here ... http://kevinclosson.wordpress.com/

Looks like I messed up his name earlier.

There's something going on with NUMA and opterons ... not sure ( but possible ) that the Itanium's could run into something similar.

I haven't looked at the notes you posted ( thanks for the effort ) perhaps they have the subject addressed already. Received on Fri Mar 06 2009 - 17:10:55 CST