Thanks Richard.
It certainly does appear to be memory related (on a smaller data set of
250K subscribers, all accesses are < 1ms).
We're going to play with increasing RAM on the machine, and applying the
optimisation levels on the page you recommended.
(We're also running on a hardware RAID controlled SCSI set - mirrored
disks so reading should be very fast).
Cheers,
Damien
