[erlang-questions] Mnesia slow down system performance when table size reaches a certain value

Solomon <>
Wed Sep 5 16:17:01 CEST 2012


My system has enough memory, is there memory limit of erlang vm?
(I run the server at 32bit os with pae patch, and the problem did not arise
at 64bit os)

2012/9/5 Michael Turner <>

> On Wed, Sep 5, 2012 at 5:33 PM, Dan Gudmundsson <> wrote:
> > Is it a bag table, If so how unique are your keys?
> >
> > Do you have an index on table, if so how unique are the secondary keys?
> >
> > Insertion time in bags are linear, (and indices are bag tables).
>
> Dan, that would explain a relatively smooth degradation in
> performance, as size goes up. What's being reported here doesn't sound
> like that. Quantum leaps in execution time are often caused by a level
> of the memory hierarchy getting maxed out, by something that's doing a
> comprehensive scan of data that, up to a point, fits in that level of
> the hierarchy. With CPU load going to (near-) zero, sounds like the
> level is that of virtual memory: thrashing, I/O bound through
> page-replacement. Even if that's the case here, the mystery is why
> deleting some records doesn't "fix" the problem.
>
> -michael turner
>
>
> > On Wed, Sep 5, 2012 at 8:02 AM, Solomon <> wrote:
> >> I set up a web server with erlang and use mnesia to save the session.
> >> I test server, at beginning, system run well and cpu load were about
> 90%.
> >> Whe session table size reached a certain value, most web requests were
> >> failure, and cpu were idle. I delete some records in session table, but
> it
> >> were not worked, then I used mnesia:clear_table/1 to clear session,
> system
> >> run normal again.
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