Too-frequent checkpoints; which parameters to check?

I've got a situation with On-Line 7.22 (SPARC, Solaris 2.5.1) where we get flurries of checkpoints at short intervals, during some update periods that look like: 23:35:07 Checkpoint Completed: duration was 2 seconds. 23:35:14 Checkpoint Completed: duration was 1 seconds. 23:35:22 Checkpoint Completed: duration was 1 seconds. 23:35:30 Checkpoint Completed: duration was 1 seconds. 23:35:38 Checkpoint Completed: duration was 1 seconds. 23:35:46 Checkpoint Completed: duration was 2 seconds. 23:35:53 Checkpoint Completed: duration was 1 seconds. ... 23:45:06 Checkpoint Completed: duration was 1 seconds. 23:45:14 Checkpoint Completed: duration was 1 seconds. Needless to say, queries slow to a crawl when there's a checkpoint every few seconds. Log files aren't a problem, but I'm not sure exactly what is... Which tuning parameters should I be looking to change: PHYSFILE, the LRU* ones, or ???