[hibernate-dev] [OGM] MongoDB time spikes

[Guillaume SCHEIBEL]

Hi all,

What do you think about using the Ehcache module to store the data between
2 flushes ?
I will open a JIRA about this point if it has not already been done.

Guillaume

2012/4/25 Emmanuel Bernard <emmanuel at hibernate.org>

> Hi Alan and all,
>
> I have been researching the spikes issue you encounter in the stress test
> from a theoretical point of view.
> You were trying a different associations storage approach (splitting
> associations as one row per document rather than the whole association per
> document). Does that return better results?
>
> I am skeptical for a few reasons. MongoDB has a global write lock per
> mongod process (they are working on a more fine grained solution). So if
> the spikes are due to lock contention, shuffling data won't help much. Also
> make sure you use MongoDB 2.0 instead of 1.8 as they yield lock on page
> fault which should solve a lot of these spikes problems.
>
> I have found this blog entry to be quite insightful
> http://blog.pythonisito.com/2011/12/mongodbs-write-lock.html
>
> Generally speaking, if all data can stay in memory, MongoDB should behave
> wonderfully.
>
> Which leads to my demo and the time difference between Infinispan 5s and
> Mongodb 20s. I can see several reasons:
>
> - we don't really batch operations in the mongodb dialect and we should.
>  We should accumulate operations and apply them at the end of the flush
> operation in one batch. That will require some new infrastructure from
> OGM's engine though
>  to tell the dialect when to "flush".
> - my VM might swap memory on disk which would explain the difference
> - or it could be that Infinispan is simply 4 times faster which would not
> be too surprising as Infinispan is in-process.
>
> Emmanuel
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