Large directory cache tuning on Windows 2003

Question

I have some questions about cache sizes for a directory server deployment (2005Q4) on Windows 2003 (customer's choice), provided that the db directory is about 2 Gb with the following layout, in bytes:
37 DBVERSION
16,384 userRoot_aci.db3
1,286,144 userRoot_ancestorid.db3
76,210,176 userRoot_cn.db3
168,583,168 userRoot_entrydn.db3
1,752,236,032 userRoot_id2entry.db3
152,354,816 userRoot_nsUniqueId.db3
16,384 userRoot_numsubordinates.db3
1,646,592 userRoot_objectclass.db3
286,720 userRoot_parentid.db3
5,398,528 userRoot_uid.db3
- changing allidsthreshold from 4000 to 65000 and reindexing doesn't impact the db directory size since I only have equality indexes on uid and cn.
- According to the tuning guide, the overall directory cache sizes should fit
in 2Gb, but the database cache size shouldn't be set to more than 1Gb.
I would rather tend to set the database cache to about 1,5 Gb and
leave the remaining memory to the entry cache (and so that the slapd.exe process does'nt exceed 2Gb), and thus I wonder what's the best/recommanded strategy in such a case ?
- Should I recommend the customer to purchase lots of memory, to profit
from the Windows 2003 filesystem cache, or should we rather rely on
hardware caches from the disks subsystem ?

Answer 1

Cyril,
Directory Server cache tuning is a very difficult art, especially on Windows and 32 bit OS...
I'm afraid we do not have a definitive answers on what is best. The answer also depend on many other parameters such as request patterns, entry size...
Favoring the db cache seems to work well with machines that are very fast and with a very performant memory allocation system.
Ludovic.