Re: NDBM :-( (Was problems...)

Tim Howes (
Tue, 18 Jun 1996 16:31:44 -0700

Russell Fulton wrote:
> What is so nasty is that the indexing fails silently. I didn't get a
> message that I have exceeded the limits so it never occured to me that
> ndbm was the problem. (Yeah, I'm still naive, I've only been in this
> business 20 odd years... err, pehaps that should be senile)
> Would it be worth adding an extra warning to the README file saying
> "Don't use ndbm unless you absolutely have to and if you do use it it
> may fail silently in mysterious ways" That avoids having to alter the
> User Guide.

Yeah, that does stink. Any future relese should include
such a warning.

> What are the advantages of Berkeley db over gdbm? Performance?
> If one does use the Berkeley package is there any preference for the
> hash or btree implementaions.

I haven't done any scientific performance testing, but one
disadvantage of using gdbm is that its free space management
is pretty bad, so your database files can tend to grow unless
you reorganize them. And I've seen a bug in gdbm that can
prevent you from reorganizing.

The other advantage of using the btree package is that
it provides an ordered retrieval method. Slapd does not
currently make use of this (e.g., to index >= or <= queries),
but we always planned to make it work. Unless you're using
an ordered data structure like a btree, this is not really

> I would like to take this opportunity of saying Thanks!! to
> The University of Michigan for making this execellent software
> available. It has allowed us to get off the ground with this project
> and provide us with a server to test mail clients against.
> Long term we may buy a commercial server but being able to 'test the
> water' cheaply and easily makes a big difference to us.
> I would also like to say a personal thanks to Tim Howes who obviously
> still maintains a keen interest in the package even though he (at
> least from his email address) no longer works for U Michigan. Thanks
> Tim and thanks to all the other helpful people on the list.

Thanks, that's nice to hear. I'll pass along your thanks
to both U-M and my new employer, Netscape, who have been
kind enough to allow my colleagues and me to spend a little
time still doing ldap support. -- Tim