We run a compaction script that compacts every database every night. 
Compaction of our biggest (0.6 TB) database took about 10 hours today. 
Granted, the hardware has poor I/O bandwidth, but even if we improve the 
hardware, a change in strategy could be good.  Along with splitting that 
database into more manageable pieces, I hope to write a compaction 
script that only compacts a database sometimes (a la Postgresql's 
autovacuum).  To do that, I want some way to estimate whether there's 
anything to gain from compacting any given database.

I thought I could use the doc_del_count returned by GET /<database-name> 
as a gauge of whether to compact or not, but in my tests doc_del_count 
remained the same after compaction.  Are there any statistics, however 
imperfect, that could help my code guess when compaction ought to be done?

Best Regards,
Wayne Conrad