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I'm afraid to increase the cachesize in DB_CONFIG:

ch_realloc means the system ran out of memory. Increasing the DB_CONFIG cachesize will run you out of memory more quickly.

I'm sitting JUST NOW in front of the LDAP Server and slapcat/slapadd the database to reorganize .. (database is almost 4 years old) 2 hours ago, booth servers crashed again ... I can't belief, that 16G RAM not enough for 1500000 entires/objects ...

I need about 5G for set_cache_size (DB_CONFIG) and the other RAM (11G) is for shared memory and the other caches (cachesize, dncachesize, idlcachesize). How much need the three caches?

And if to less cache, the machines should run slower, but not run out of memory?

The best thing for you to do would be to upgrade to OpenLDAP 2.4.33 and switch to using back-mdb.

Softwareupdate is possible not before january 2013. I was wrong with the version, we use 2.4.31 I'm looking to mdb since a few month, but is it usable for production?

If you are not capable of doing that, I would suggest you use tcmalloc as an alternative memory allocator to glibc, and reduce your entry cachesize and idlcachesize. If you can reclaim enough space, you should increase your DB_CONFIG cachesize, as that is the most important element of performance with back-bdb/hdb.

Yes, not before january 2013 ... Hope after reorganization, slapd runs more stable... The only thing I can do for now.

Thanks Meike