[GitHub] metron issue #990: METRON-1520: Add caching for stellar field transformation...

[cestella <gi...@git.apache.org>]

Github user cestella commented on the issue:

    https://github.com/apache/metron/pull/990
  
    This PR provides an expression cache for stellar when using the stellar field transformations in parsers.  Specifically, we found that without caching we were substantially stymied when performance tuning enrichments.  Thus, other places where stellar is in the critical path might derive benefit from similar caching in Enrichments.
    A couple of points about the implementation:
    * We use the same underlying caching strategy as in enrichments (caffeine-based least frequently used cache).
    * This caching is implemented in stellar core as an alternative to the StellarProcessor.  This way it is reusable elsewhere that stellar is used eventually.
    * This caching is slightly different than the caching in enrichments in that:
      * Enrichment caching is done regardless of adapter (stellar enrichments uses the same cache as the hbase enrichments)
      * Enrichment caching for stellar is at the group level (e.g. the key is the group of stellar expressions and the input variables used in the group adn the value is the set of results for that group given the input).  This implementation is at the individual expression level.


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