Quoting Dieter Kluenter <dieter@dkluenter.de>:
Is there any chaining, back-ldap or back-meta involved?
On the consumer, I'm using the chain overlay, which requires the back_ldap module. The large numbers of open file descriptors occur on both the consumer and the provider, although this may be symptomatic.
I am not aware of any FD leak, although 2.4.11 is rather old (July 2008). As since then numerous syncrepl bugs have been fixed, you should probably update to 2.4.21
I'll give it a spin and see if it makes a difference. Cheers, Jaap