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Re: Default threads value in OpenLDAP



--On Wednesday, April 18, 2007 1:43 PM -0700 Howard Chu <hyc@symas.com> wrote:

Quanah Gibson-Mount wrote: 
After extensive benchmarking by both Howard & I, it seems the default
value  for the threads setting in OpenLDAP (16) is excessive for most
hardware.  Unless someone has plenty of CPUs (at least 4+, not counting
fake HT CPUs),  slapd performance is significantly improved by running
at 8 threads.  Recent tests done by Howard indicated that dropping the
number of threads  to 4 on my 2 CPU boxes further improved read
performance, but I haven't had  the time to do the corresponding write
performance tests to see how they  were impacted.  In any case, the "8"
value is definitely better for both  read & write performance for 1 & 2
CPU servers (and possibly 4, I just  haven't had one to experiment on).
The only time I've found a need to  increase the number of threads was
when I was benchmarking the Sun T2000,  which had 32 cores.  Given all
of this, I'd like to propose that we change

SLAP_MAX_WORKER_THREADS

in slap.h from 16 to 8 for OpenLDAP 2.4.

Thoughts? 

I think we should leave this alone until we have read/write test results
to confirm things. Also, our testing was primarily on Linux 2.6; other
platforms may have more efficient thread scheduling.

I reached the same conclusions on my old Solaris V120's, with RW tests too. ;) If we get that build farm proposal, that might be a good opportunity to do some testing of small DB's on a variety of platforms, I suppose. However, I'm guessing the majority of OpenLDAP users fall into the Linux and Solaris categories.

--Quanah

--
Quanah Gibson-Mount
Senior Systems Software Developer
ITS/Shared Application Services
Stanford University
GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html