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Re: Default threads value in OpenLDAP
Buchan Milne wrote:
On Wednesday 18 April 2007, Quanah Gibson-Mount wrote:
--On Wednesday, April 18, 2007 11:49 PM +0200 Raphaël Ouazana-Sustowski
Le Mer 18 avril 2007 23:17, Quanah Gibson-Mount a écrit :
What sort of tests are you doing ?
I reached the same conclusions on my old Solaris V120's, with RW tests
;) If we get that build farm proposal, that might be a good opportunity
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.
A series of tests where I have mixed read/write ratios. In particular:
30% read, 70% write
50% read, 50% write
70% read, 30% write
with multiple increasing numbers of threads.
And, how many databases ?
I assume the recommendation is based on one database? In my deployment, I have
3 relatively large databases (~400 000, ~500 000, ~800 000), so since better
performance at the reduced thread number is probably due to reduced database
contention, 24 threads may be more appropriate for me?
Or, should the number of threads be configurable at the database level ?
That wouldn't make any sense, since threads are a global resource for
the process. Also, a single operation can span multiple databases (e.g.
using glue/subordinate) so there's really no point to that.
It really comes down to read vs write contention. With the current entry
cache in OpenLDAP 2.4, I can get a single client to read an entire
380,000 entry database (contained completely in the back-bdb entry
cache) in only 0.70 seconds. On the same system (which has a dual-core
processor) two clients can perform the same search in 0.71 seconds.
I.e., database contention is almost nonexistent. The real problem seems
to be that thread scheduling overhead is too high relative to the CPU
cost of a single LDAP read operation. When you have a large number of
slower operations (e.g. writes with a lot of index updates) then the
thread overhead becomes proportionately smaller.
-- Howard Chu
Chief Architect, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/