Re: Multi Master Enviornment for Openldap 2.3

[Quanah Gibson-Mount <quanah@stanford.edu>]

--On Friday, February 02, 2007 11:29 AM +0200 Buchan Milne 
<bgmilne@staff.telkomsa.net> wrote:

> Hmm, I load balance OpenLDAP 2.3. Why ? Because, on the occasions we have
> heavy writes (averaging 30-40 modifications per second over a few hours),
> one  slaves isn't guaranteed to respond to our radius servers within the
> time we  have to send a response back to the radius proxy. Under the high
> write load,  1 slave would not handle the full read load (about 1000
> operations per  second), but each slave can normally still handle about
> 250 operations per  second without too much delay.
>
> Sure, pure read performance is much higher than I need (easily 10000
> searches/sec on boxes with no write load), but you need to consider
> worst-case load over the entire lifetime of the installation, and write
> load  can have a big impact.

There are other reasons to load balance, as well.  Consider 24/7 uptime 
requirements.  If I have only 1 server, that is a SPOF.  Even if I have 2 
servers, the risk of not meeting the 24/7 needs rather great.  At Stanford, 
we have one master, isolated for nearly pure write purposes, 1 HA Standby 
master (waiting on 2.4), and 4 replicas that are geographically diverse. 
This also means I can upgrade the entire replica cluster with no outage. 
And of course, as Buchan notes, if there was a high volume of writes to hit 
the servers, this helps mitigate the impact.

And although OpenLDAP is blazingly fast, when you start throwing things in 
like SASL/GSSAPI binds, your performance can take a major hit.  Although my 
hardware can sustain 15,000 authorizations/second with simple binds (30,000 
searches/second), it drops to 100 searches/second with SASL/GSSAPI in play 
if the application connects, binds, searches, disconnects.  If it uses 
persistent connections, then it is again blazingly fast, since the 
massively slow bind step is removed.

--Quanah

--
Quanah Gibson-Mount
Principal Software Developer
ITS/Shared Application Services
Stanford University
GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html