The Unbearable Slowness of Some disc_only_copies Transactions

adam <>
Tue Dec 8 06:19:01 CET 2009


Multiple volumes. We ended up creating several Erlang nodes on the
same machine, one for each volume, then we relied on mnesia_frag to
distribute table fragments evenly over the Erlang nodes, and hence
over the EBS volumes.

On Dec 7, 7:28 pm, Garrett Smith <> wrote:
> Do you mean mount a single volume on multiple EBS partitions (e.g.
> raid-0) or to explicitly store different Mnesia tables/fragments on
> multiple volumes?
>
>
>
> On Mon, Dec 7, 2009 at 5:02 PM, adam <> wrote:
> > Not sure if this will help anyone else, but there are two parts to the
> > solution I used for this:
>
> > 1) Use +A [Num threads] with erl to increase the number of
> > asynchronous threads for IO. (Thanks to Valentin Micic for this one)
> > 2) If using a file store like EBS, distribute the database across
> > several EBS volumes.
>
> > Adam
>
> > On Dec 2, 10:24 pm, adam <> wrote:
> >> We have running Erlang code that is executing about 30 transactions
> >> per second. Each transaction puts a write lock on a couple of records,
> >> then performs a read and a write. We need to hold several hundred
> >> million records simultaneously.
>
> >> When using disc_copies tables, we can easily manage to run about 160
> >> transactions per second. We also see that each transaction takes an
> >> average of about 750-1400 microseconds to run. Min time is 350
> >> microseconds, and max time seems to go between 30-100 milliseconds.
>
> >> However, with disc_only_copies tables, individual transaction time
> >> ranges between 500 microseconds up to about 90 seconds(!). Why do
> >> individual transactions sometimes take such a long time with
> >> disc_only_copies?
>
> >> Thank you!
> >> Adam
>
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>
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