Hi Taliesin
Thanks very much for your help.

I have run the check indexes utility and it reports no problems.

We have 333 active courses, around 5500 users in the user table but not all
are active.  I never know how to measure "activity" but 2405 different users
have logged on since 1 April and we have around 1000 - 1400 logins a day.

The excessive memory usage I reported is for Apache (and we get errors in
the log "ADODB Error: Database connection failed". This happens once or
twice a week at the moment but seems to be increasing.  It looks like it
happens when a lot of students are trying to access the system around the
same time eg when we put the student satisfaction survey on Moodle. 
Currently the httpd process is 166k, but not many users are logged on.  I
increased max_connections to 200 in postgresql.conf but it didn't help.  

We also have an issue with slow login times (now > 30 seconds), this has
increased over the last couple of months - it used to be a lot faster.

Apart from these issues everything else runs well except when we experience
the memory problems.

Regards
Barbara