Re: commit: ldap/doc/man/man5 slapd-bdb.5

[Howard Chu <hyc@OpenLDAP.org>]

Gavin Henry wrote:
> <quote who="hyc@OpenLDAP.org">
> > Update of /repo/OpenLDAP/pkg/ldap/doc/man/man5
> >
> > Modified Files:
> > 	slapd-bdb.5  1.36 -> 1.37
> >
> > Log Message:
> > Add dncachesize
>
> A new one for the tuning section. Will add soon.
>
> Also, in the e-mail titled "Maximum size of the database."
>
> - What is the maximum size of the database that OpenLDAP can support ?
> - What is the maxmum number of dns it can hold ?
>
> For the Tuning section and General info in out Guide, how does someone
> calculate the above?
>
> I'm interested as you said, "For a machine with 4GB of RAM I think it will
> max out at around 1-2 million DNs."
>
> What is the rule of thumb for above?

I probably misspoke. See 
http://www.openldap.org/lists/openldap-software/200611/msg00051.html instead.

A back-bdb EntryInfo node on a 32 bit machine is around 64 bytes, not including 
the length of the RDN stored in the node. (For back-hdb the node is about 20 
bytes larger). Assuming an average RDN length of 20-30 bytes, that makes each 
node around 100 bytes total. So 1 million DNs would consume about 100MB, and 10 
million DNs would consume about 1GB.

On a 32 bit machine a user process typically can only address 2GB of memory, 
though you can sometimes tweak that up to 3GB.

Of course if your average RDN length is shorter, then you can cache more within 
those constraints. Likewise, if you're running a 64 bit OS, your process 
address space has much higher limits, far higher than anyone is likely to bump 
into.
--
  -- 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/