From: Kazakin, Leon (Leon.Kazakin@CIBC.ca)
Date: Fri Dec 19 2003 - 15:33:22 EST
Thank you all.
I copy 2 most helpful responses here.
=================================================================
> I was approached by a DBA and requested to increase shmmax
> from 1,53GB to 3 GB on 4GB RAM N class and 5 GB on 6GB RAM N class.
Hummm. If the DBA is really going to use all that shared memory, the
performance will be AWFUL since data and processes will always be
swapping in and out. You can set shmmax to a large value and then
increase Sybase's use of the memory until page-outs (from Glance or
vmstat) start moving into the double digit area for many minutes.
> Those systems run 64-bit Sybase and that's pretty much it for the
workload.
> It's HP-UX 11.
It doesn't matter what application you are using. You'll need several
dozen
megs for the opsystem, several hundred (up to about 500 max) for the
buffer cache and a few megs for the applications. Generally, having one
VERY large share memory segment is not too efficient unless you enable
large memory pages for the Sybase executables that will access this
memory. Otherwise, you'll get a lot of TLB misses (called page faults in
Glance). This is a hardware register issue and definitely needs to be
considered for massively large data areas. The chatr program can change
an executable to utilize large memory pages.
Bill
--
Best regards,
Bill Hassell (blhconsulting@mindspring.com)
=================================================================
From: Abramson, Stuart
I think that the rules are the same. If you are using 64 bit applications
you can use big shared memories.
I would see what the system runs "empty" with glance, and then set shmmax to
the remainder. There's not a lot of point to swapping out your shared
memory.
# /usr/contrib/Q4/bin/kmeminfo
kmeminfo (3.11)
libp4 (5.17): Opening /stand/vmunix /dev/kmem
Loading symbols from /stand/vmunix
======================================================================
Date: Thu Dec 18 14:08:05 2003
Processing pfdat table (2042785 entries)...
----------------------------------------------------------------------
Physical memory usage summary (in pages):
Physmem = 2097152 Available physical memory:
Freemem = 1091460 Free physical memory
Used = 1005692 Used physical memory:
System = 451878 by kernel:
Static = 54367 for text and static data
Dynamic = 183653 for dynamic data
Bufcache = 209715 for file-system buffer cache
Eqmem = 47 for equiv. mapped page pool
SCmem = 4096 for system critical page pool
User = 507069 by user processes
Uarea = 4440 for thread uareas
Disowned = 50864 disowned pages
A "page" is 4096 bytes:
. My kernel uses 451878 x 4096 bytes/page = 1.8 GB
. My pesky users use 507069 x 4096 bytes/page = 2.X GB
So, I could set shmmax to 4 GB on an 8 GB machine.
You want to ensure that your maxdsiz_64 and his little friends (_64 friends)
are set correctly.
Stuart
-----Original Message-----
From: hpux-admin-owner@DutchWorks.nl [mailto:hpux-admin-owner@DutchWorks.nl]
On Behalf Of Kazakin, Leon
Sent: Thursday, December 18, 2003 1:57 PM
To: 'hpux-admin@dutchworks.nl'
Subject: [HPADM] Sybase and shared memory
Hi all,
I was approached by a DBA and requested to increase shmmax from 1,53GB to
3 GB on 4GB RAM N class
and
5 GB on 6GB RAM N class.
Those systems run 64-bit Sybase and that's pretty much it for the workload.
It's HP-UX 11.
I have some Oracle tuning experience, but none with Sybase.
Any thoughts?
--
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