slapd becoming mysteriously slow

[Johan Jönemo <johan.jonemo@hep.lu.se>]

I have made a test package to see if people understanding openLDAP
better than I do can reproduce and possibly explain the strange behavior
I have been plagued by.

I run an application that updates a directory more or less continuously
and it runs at a reasonable speed. Often this can last for hours. Then
everything slows down drastically (by more than a factor 10) in one
instant (i e it doesn't slow down gradually). I think that slapd spends
long times in some kind of waiting state. I base this on the fact that I
can induce the behaviour regardless of which of a large number of
methods I have tried on the "client" side, i e the application updating
the directory. I have tried calling the ldap client tools from shell
scripts and using the API with perl bindings and so on. The WCHAN seem
to be the same most of the time that te application is slow.
Unfortunately I wasn't able to make any sense of this numerical
information (I'm not too familiar with kernels and such).

I have got this behaviour with different versions of openLDAP I have
tried (the newest being 2.3.32). Different Berkley db packages in the
range 4.3-4.5 didn't seem to matter. The instructions for the package
can be found at:

http://www.hep.lu.se/staff/jonemo/README.txt

And the test package itself at:

http://www.hep.lu.se/staff/jonemo/cached-dryrun.tar.bz2

It does a none intrusive set-up in order to set some paths but it
doesn't copy anything to outside its own directory. It starts an
instance of the local slapd on a non-standard port using its own
configuration and schema.

I would be very interested if anyone would try out this package and see
if they can explain the behavior (or reproduce it at all, as the case
may be).

Thanks in advance

Johan Jönemo