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Many entries, deletes getting painfully slow


I have a database with close to 11 million entries and lately deletes have started to get painfully slow. I've set up a new server with a lot of improvements, but if anyone have an idea about what the deciding factor for the performance difference is, then I would be grateful.

On the old server:
-16 cores. 42Gb RAM, entire database in memory
-XFS file system on (hw)RAID-1
-Database and BerkeleDB log on same filesystem
-some, but not much load (~35 read waiters)
-time to delete 157 entries: 9 minutes.

New server:
-16 cores, 48Gb RAM, entire database in memory
-ext3 filesystem on (hw)RAID-10
-Database and log on difference disk
-no load.
-time to delete the same 157 entries: 6.2 seconds

I'm aware that the new server has all the benefits, but even under low load conditions, the old server is only able to delete an entry every 3 seconds and there's orders of magnitude difference between 6 and 540 seconds.

My suspicion is that there's one of the above factors (XFS?, db/log on same fs?) which get very pronounced when the database gets above a certain size, since this slowdown for deletes seem to have accelerated with the growth of the database the last few months.