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From Sivaramakrishnan Narayanan <tarb...@gmail.com>
Subject Re: Caching metastore objects
Date Wed, 27 May 2015 05:12:29 GMT
Thanks for the replies.

@Ashutosh - thanks for the pointer! Yes I was running 0.11 metastore. Let
me try with 0.13 metastore! Maybe my woes will be gone. If they don't then
I'll continue working along these lines.

@Alan - agreed. Caching MTables seems like a better approach if 0.13
metastore perf is not as good as I'd like.

@Scott - a pluggable hook for metastore calls would be super useful. If you
want to generate events for client-side actions, I suppose you could just
implement a dynamic proxy class over the metastore client class which does
whatever you need it to. Similar technique could work in the server side -
I believe there is already a RetryingMetaStoreClient proxy class in place.


On Wed, May 27, 2015 at 7:32 AM, Ashutosh Chauhan <hashutosh@apache.org>
wrote:

> Are you running pre-0.12 or with hive.metastore.try.direct.sql = false;
>
> Work done on https://issues.apache.org/jira/browse/HIVE-4051 should
> alleviate some of your problems.
>
>
> On Mon, May 25, 2015 at 8:19 PM, Sivaramakrishnan Narayanan <
> tarball@gmail.com> wrote:
>
> > Apologies if this has been discussed in the past - my searches did not
> pull
> > up any relevant threads. If there are better solutions available out of
> the
> > box, please let me know!
> >
> > Problem statement
> > --------------------------
> >
> > We have a setup where a single metastoredb is used by Hive, Presto and
> > SparkSQL. In addition, there are 1000s of hive queries submitted in batch
> > form from multiple machines. Oftentimes, the metastoredb ends up being
> > remote (in a different region in AWS etc) and round-trip latency is high.
> > We've seen single thrift calls getting translated into lots of small SQL
> > calls by datanucleus and the roundtrip latency ends up killing
> performance.
> > Furthermore, any of these systems may create / modify a hive table and
> this
> > should be reflected in the other system. Example, I may create a table in
> > hive and query it using Presto or vice versa. In our setup, there may be
> > multiple thrift metastore servers pointing to the same metastore db.
> >
> > Investigation
> > -------------------
> >
> > Basically, we've been looking at caching to solve this problem (will come
> > to invalidation in a bit). I looked briefly at DN's support for caching -
> > these two parameters seem to be switched off by default.
> >
> >     METASTORE_CACHE_LEVEL2("datanucleus.cache.level2", false),
> >     METASTORE_CACHE_LEVEL2_TYPE("datanucleus.cache.level2.type", "none"),
> >
> > Furthermore, my reading of
> > http://www.datanucleus.org/products/datanucleus/jdo/cache.html suggests
> > that there is no sophistication in invalidation - seems like only
> > time-based invalidation is supported and it can't work across multiple
> PMFs
> > (therefore, multiple thrift metastore servers)
> >
> > Solution Outline
> > -----------------------
> >
> >    - Every table / partition will have an additional property called
> >    'version'
> >    - Any call that modifies table or partition will bump up version of
> the
> >    table / partition
> >    - Guava based cache of thrift objects that come from metastore calls
> >    - We fire a single SQL matching versions before returning from cache
> >    - It is conceivable to have a mode wherein invalidation based on
> version
> >    happens in a background thread (for higher performance, lower
> fidelity)
> >    - Not proposing any locking (not shooting for world peace here :) )
> >    - We could extend HiveMetaStore class or create a new server
> altogether
> >
> > Is this something that would be interesting to the community? Is this
> > problem already solved and should I spend my time watching GoT instead?
> >
> > Thanks
> > Siva
> >
>

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