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https://issues.apache.org/jira/browse/METRON-1460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16383872#comment-16383872
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ASF GitHub Bot commented on METRON-1460:
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Github user arunmahadevan commented on the issue:
https://github.com/apache/metron/pull/940
Managing threadpools within a bolt isn't fundamentally wrong, we have see
some use cases where this is done. However, we have been putting efforts to
reduce the overall number of threads created internally within storm since the
thread context switches were causing performance bottlenecks. I assume the
threadpool threads are mostly IO/network bound so it should not cause too much
harm.
Do you need multiple threads since the enrichments involve external DB look
ups and are time consuming ? Maybe you could compare the performance of
maintaining a thread pool v/s increasing the bolt's parallelism to achieve a
similar effect.
Another option might be to prefetch the enrichment data and load it into
each bolt so that you might not need separate threads to do the enrichment.
If you are able to manage without threads, that would be preferable. Even
otherwise its not that bad as long as you don't create too many threads and
they are cleaned up properly. (we have had some cases were the internal threads
were causing workers to hang).
> Create a complementary non-split-join enrichment topology
> ---------------------------------------------------------
>
> Key: METRON-1460
> URL: https://issues.apache.org/jira/browse/METRON-1460
> Project: Metron
> Issue Type: New Feature
> Reporter: Casey Stella
> Priority: Major
>
> 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
> tuning
> * 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 topology.
> 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
> enrichments
> * 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 start_enrichment_topology.sh 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.
>
>
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