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Re: Many entries, deletes getting painfully slow

Peter Mogensen <apm@mutex.dk> writes:

> Hi,
> 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.

To my opinion there are three factors which have influence on
- keeping db transaction logs on a different disk reduces writes on
  the database disk,
- ext3 vs. xfs, xfs is known to be slower than ext3 in handling small
- raid-10 provides a small gain in performance, if disk caching is
  configured properly.


Dieter Klünter | Systemberatung