Re: RE: increasing number of sessions vs. processes

  • From: Jesper Haure Norrevang <jhn.aida@xxxxxx>
  • To: Paula_Stankus@xxxxxxxxxxxxxxx
  • Date: Wed, 19 Jan 2005 18:24:32 +0100


Comments inline.

> There is a relationship between sessions on a database and the 
> number of
> processes.  What happens if we increase the number of sessions without
> increasing the number of processes???

The parameters SESSIONS and PROCESSES determine the
size of two arrays in the SGA.

If you try to create more sessions on an instance than specified
by the SESSIONS  parameter, you will get an ORA-00018: maximum
number of sessions exceeded.

If you try to create more processes on an instances than specified
by the PROCESSES prameter, you wil get an ORA-00020: maximum
number of processes exceeded.

The number of sessions and processes on your instance can been
seen using a COUNT(*) against V$PROCESS and V$SESSION.
Your job is to determine resonable values, so your users can continue
to work without getting neither ORA-18 nor ORA-20 during normal
conditions. (A run away job, that keeps starting new sessions is not
a normal condition, and it should be stopped by ORA-18 or ORA-20
whichever happens first).

You can join the two V$-views using the columns V$SESSION.PADDR

It is quite normal to see a 1:1 relationship between processes
and sessions. However one OCI-program can create multiple
sessions belonging to one process. Users of Oracle Portal
will experience this behaviour.

The default value for SESSIONS is 1.1*PROCESSES + 5. 
It is appropriate for some databases and inappropriate for
others (e.g. Oracle Portal).

> Also, I remember a limit on the OS regarding the number of processes
> allowed per Oracle user - also I know there is a semaphore 
> relationship.

On HP-UX there is a kernel parameter called NPROC. Like
PROCESSES and SESSIONS it should have a reasonable

Hope this helps.

Jesper Haure Norrevang


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