IIslave processes

> priyeshp@aol.com (PRIYESHP) wrote:
> 
> > I was under the impression that ingres made best use of slave processes
> > when they were configured as an even number. .....
> 
> I was told this once too.  When I inquired further, another person in
> Level 2 support (whom I will not name, if he wishes to put in his 2 cents
> publicly that's his affair) said that "it sounded like voodoo to him".
> 
> Also, I wouldn't use RAID 5 for Ingres myself, having been burned by
> its poor write performance.  If it works for you, fine.  If you have
> 5 drives I would probably try for 4 or 5 slaves;  but this number is
> a) quite dependent on the characteristics of the RAID subsystem, and
> b) not all that critical anyway, as near as I can tell.

In a very I/O intensive system, with lots of active, concurrent
sessions, more slaves may improve performance.  I've seen up to 3 slaves
per spindle used effectively, allowing intelligent controllers to
optimize seeks.  Few real systems are I/O intensive enough to see much
benefit, though.  

RAID complicates things a bit, but the principles still hold true. 
Another post mentions tuning the number of slaves by adding more until
the last one is not used.  That technique works as well as any.  The
cost of overconfiguring the slaves is mainly in the wasted process that
an idle slave represents, and a trifling amount of wasted swap space. 
If you aren't tight on resources, don't worry about having one or two
more slaves than is ideal.
> 
> Karl Schendel
> Telesis Computer Corp

-- 
Jerry Lohr                           Silicon Graphics, Inc.
Email:  glohr@engr.sgi.com           2011 N. Shoreline Blvd.  08L-855
Phone:  +1 415 933 4661              Mountain View, CA 94043-1389




        The number of slaves you have is defined by the environment
        variable II_NUM_SLAVES. Normally you have 2 of them or at least
        one for every database disk. The dbms-process forks them. I don't have 
        the code, so I don't know if they try to become daemons after forking.
        The slave processes are a substitute for the lack of asynchonous I/O 
        (a matter of history as you see). OI uses AIO if available and doesn't 
        need slaves in such a case.

	Ronald Jeninga
	Jeninga@t-online.de
Ingres Q & A
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