GitHub user cestella opened a pull request:

    Single bolt split join poc

    ## Contributor Comments
    There are some deficiencies to the split/join topology.
    It's hard to reason about
    * Understanding the latency of enriching a message requires looking at 
multiple bolts that each give summary statistics
    * The join bolt's cache is really hard to reason about when performance 
    * During spikes in traffic, you can overload the join bolt's cache and drop 
messages if you aren't careful
    * In general, it's hard to associate a cache size and a duration kept in 
cache with throughput and latency
    * There are a lot of network hops per message
    * Right now we are stuck at 2 stages of transformations being done 
(enrichment and threat intel).  It's very possible that you might want stellar 
enrichments to depend on the output of other stellar enrichments.  In order to 
implement this in split/join you'd have to create a cycle in the storm topology
    I propose that we move to a model where we do enrichments in a single bolt 
in parallel using a static threadpool (e.g. multiple workers in the same 
process would share the threadpool).  IN all other ways, this would be 
backwards compatible.  A transparent drop-in for the existing enrichment 
    There are some pros/cons about this too:
    * Pro
      * Easier to reason about from an individual message perspective
      * Architecturally decoupled from Storm
      * This sets us up if we want to consider other streaming technologies
      * Fewer bolts
        * spout -> enrichment bolt -> threatintel bolt -> output bolt
      * Way fewer network hops per message
    currently 2n+1 where n is the number of enrichments used (if using stellar 
subgroups, each subgroup is a hop)
      * Easier to reason about from a performance perspective
      * We trade cache size and eviction timeout for threadpool size
      * We set ourselves up to have stellar subgroups with dependencies
    i.e. stellar subgroups that depend on the output of other subgroups
    If we do this, we can shrink the topology to just spout -> 
enrichment/threat intel -> output
    * Con
      * We can no longer tune stellar enrichments independent from HBase 
        * To be fair, with enrichments moving to stellar, this is the case in 
the split/join approach too
      * No idea about performance
    What I propose is to submit a PR that will deliver an alternative, 
completely backwards compatible topology for enrichment that you can use by 
adjusting the `` script to use 
`remote-unified.yaml` instead of `remote.yaml`.  If we live with it for a while 
and have some good experiences with it, maybe we can consider retiring the old 
enrichment topology.
    To test this, spin up vagrant and edit 
`$METRON_HOME/bin/` to use `remote-unified.yaml` 
instead of `remote.yaml`.  Restart enrichment and you should see a topology 
that looks something like:
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You can merge this pull request into a Git repository by running:

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    This closes #940
commit a4f618a3ad895d62772366e0e93e5b8b37c5c964
Author: cstella <cestella@...>
Date:   2018-02-21T23:59:16Z

    Adding parallel enrichment bolt.

commit 99fe0b86005fe04294b3851a17ae3d88f228c5d2
Author: cstella <cestella@...>
Date:   2018-02-22T00:21:06Z

    Updating to include trace statements.

commit 79736c6f3fab04d01dd1eb998b308f438003a0e1
Author: cstella <cestella@...>
Date:   2018-02-22T15:35:44Z

    Updating with some cleanup

commit cb4a527c9146865dafad1d597ba93032ef398d94
Author: cstella <cestella@...>
Date:   2018-02-22T15:48:11Z

    Updating spec.

commit fb4d4383f366776f446e33a422652c3ec1f56bfa
Author: cstella <cestella@...>
Date:   2018-02-22T18:00:36Z

    Updating threadpool creation

commit 87ef6a72827c31f8adee42ee71272a32c350bc1f
Author: cstella <cestella@...>
Date:   2018-02-22T18:04:37Z

    better docs



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