METRON-820: StellarProcessor should have a static expression cache

[cestella]

Contributor Comments

We recreate StellarProcessor objects all over the place which do not reuse their expression caches. This results in a significant performance regression as we are compiling the expression and then processing for every message, rather than compiling once and reusing.

As far as testing, unit tests cover this functionality quite a bit. Also, a smoke-test with vagrant is in order (i.e. ensuring data flows through the topology) with a field transformation and a stellar enrichment set.

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[ottobackwards]

1 question -> does this require any relation to the VFS cache?

[cestella]

@ottobackwards It should not. When we start being able to handle people dropping new jars in HDFS on a running topology, then we will need to prune this cache. As of now, though, a new jar in HDFS requires a topology restart, so this cache would always be fresh.

[ottobackwards]

+1 by inspection, although I'm inclined to think of a reason not to have a static cache, but instead an instance based one, I can't think of a specific case.

[mmiklavc]

Any implications to having a static cache initialized and unused if an alternate cache is passed in via the other constructors?

[cestella]

None other than the fact that we might have an empty guava cache hanging around in memory. At the moment, nobody uses the alternative cache.

[mmiklavc]

+1 by inspection