Re: reliability of LDAP lookups

[kunkee@neosoft.com (Randy Kunkee)]

> Hugo.van.der.Kooij@caiw.nl wrote:
> 
> > On Sat, 28 Oct 2000, Pierangelo Masarati wrote:
> >
> > > I use an OpenLDAP server to check whether or not a user can send mail
> > > outside of the company. Actually, there are a set of replicas of the
> > > main
> > > server that are used for many different purposes, so it happens they are
> > > very
> > > busy, so sendmail hangs waiting for reply and eventually times out.
> > > For those who are not familiar with LDAP API, a client can be configured
> >
> > Seems to me you are searching on non-indexed attributes. As I understood
> > from various postings it will make a very significant difference in speed.
> 
> Actually, it's not! It's more like a bug than a performance problem, but it
> happens
> very often that one server for a while is kind of hung: it still accepts
> connections,
> and eventually replies, but it may take a few seconds. After a while
> everything is ok.
> I've spent a lot of time trying to track the problem down. This is one of the
> reasons
> we use many servers (we are giving directory access to a lot of service for
> sendmail
> routing address, smtpauth (testing), imap auth, proxy auth, proxy redirect,
> web auth,
> app profiling, address booking and so for some 25,000 users. The servers are
> VERY
> loaded and maybe this is the only reason. At present I'm using
> OpenLDAP 1.2.11
> and testing OpenLDAP 2.0.x; in 1.2.11's slapd.conf I set
> 
> > index <binary attrs> none
> > index default pres,eq,sub,approx
> 
> so I'm positive it's not an indexing problem!
> 
> Moreover, I think the possibility to try another server in the list not only
> in case of no availability, but also in case of timeout or in general for
> application
> dependent reasons would give developers more flexibility.
> 
> Bye, Pierangelo.

It would not be difficult to write a function that would rotate between
a number of entries in the host list.  In fact, you could experiment with
writing your own function (or modifying one of the low-level functions in
the client library) to have a static int that increments each time it is
called, such that the open tries:

	host[0] thru host[n]
then	host[1] thru host[n], host[0]
and	host[2] thru host[n], host[0] thru host[1]
	etc.

This might also have a nice affect of balancing load between a number
of replicas.  Optimally, this could become a new option, eg. an
LDAP_API_FEATURE_X_OPENLDAP_ROUND_ROBIN or something like that,
with a default behavior configured at compile time.

Randy