There is some discussion on how to improve this situation occurring on
the roundup-devel list.

See:

  https://sourceforge.net/p/roundup/mailman/message/31511901/

titled: warm_cache call initial results and failures

for a prototype of a mechanism to replace many single
item loads with a batch item load that provides a speedup.

Also see:

  https://sourceforge.net/p/roundup/mailman/message/31511633/

titled: Re: load spikes due to user lookup

for tuning to make sure that the rdbms cache is correctly tuned for
your workload along with background discussion on the thread
that lead to the warm_cache implementation.