Conference futurs::sybase

    Here are parameters that set up for Sybase 11.0.2/DUNIX 4.0b benchmarks
    on the AS8400.
    rt:
    aio-max-num=1024
    ipc:
    shm-seg=1024
    shm-max=2147483136
    ssm-threshold=0
    
    If ssm-threshold is not set to 0, you won't be able to startup the
    server after configuring a new server.
    
    Also, you may want to increase maxuser, max-proc-per-user, 
    per-proc-address-space, max-vas, etc... depending on the workload.
    
    

               <<< Note 499.1 by LABC::NGUYEN "benchmark man" >>>
                       -< ssm-threshold=0 , definitely! >-

	Many thanks!  This is a 4100 with 1 GB of memory,
	
	current settings are:

	rt:
	aio-max-num=1024
	ipc:
	shm-seg=32
	shm-max=943718400
	shm-threshold=943718400

	This is not a benchmark, but a production system.  All users
	come over the Internet using ODBC to access Sybase, they
	do not login as Unix users to the system.  maxusers is
	set to 256 in the kernel conf file.  Any suggestions on
	these other parms ?

	thanks,

	...larry



>>    Here are parameters that set up for Sybase 11.0.2/DUNIX 4.0b benchmarks
>    on the AS8400.
>    rt:
>    aio-max-num=1024
>    ipc:
>    shm-seg=1024
>    shm-max=2147483136
>    ssm-threshold=0
    
>    If ssm-threshold is not set to 0, you won't be able to startup the
>    server after configuring a new server.
    
>    Also, you may want to increase maxuser, max-proc-per-user, 
>    per-proc-address-space, max-vas, etc... depending on the workload.
    
    

    re: shared memory/gh-chunks
    
The following are what I have been gathering from the Digital UNIX notes
plus my experience with SYBASE and DUNIX 4.0+.

For Digital UNIX V4.0+, there are three implementation of shared
memory: general (no shared PTEs & pageable), granularity hints (shared PTEs,
non-paged, 8 MB alignment), and segmented shared memory (shared PTEs, paged,
8MB alignment).

The default shared memory method is segmented. It seems that the
SYBASE does not work well with 8MB alignment restrictions. Therefore,
the sgemented shared memory (ssm) should be turned off by setting ssm-threshold
to 0. This will cause all shared memory requests to use the general
method instead.

The general method has no alignment restrictions. However, if you have
a large numbers of users and a large shared memory size, the connect/
disconnect performance problem may cause the system to hang or panic.
The connect/disconnect performance refers to n users connecting/disconnecting
from a shared memory segment of size s in time t. I heard numbers something
    like n=200,s=10GB,t=2.

The granularity hint method (GH) should be used in this case. Granularity
hints is a Translation Buffer (TB) optimization that allows to map more
than a single page. The benefit is a lower rate of TB misses/files. The ORACLE
TPC benchmark runs showed an improvement about 4% with granularity hints.
I have no data for Sybase. To enable GH, set ssm-threshold to 0 and gh-chunks
to the number of 512 page chunks in the shared memory region. There is no
    known connect/disconnect problems for the GH method.
    
    For Digital UNIX Version 3.2+, the segemented shared memory (ssm) is
    not available. Granularity hints is available via a patch.

    
    

	Many thanks for the clear explanation!
	Customer set SSM-THRESHOLD=0 and has been
	running without problems so far.  

	Someone needs to get this word to Sybase - one
	of their support reps was the one who said that
	ssm-threshold should be set to the same value 
	as shmmax !

	Now if we can get Sybase to recompile System 11
	on a 4.0 system !!    
    

	...larry

    Not only Sybase, but Oracle and Informix have a similar problem 
    with the segmented shared memory on the DUNIX V4.0+. The fix for
    now is to set ssm-threshold=0.