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https://issues.apache.org/jira/browse/CASSANDRA-10993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15425038#comment-15425038
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Jonathan Ellis commented on CASSANDRA-10993:
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Isn't this a good example of a case where we can start with an off the shelf
API (Rx, or Reactor) and optimize later? Given that the approach won't change
qualitatively, we can always refactor method names to a differently library
easily enough.
If we have strong evidence that off the shelf is crap (and I think Tyler's
tests show it's decent enough to be competitive with state machine, at least),
AND that we know enough to build it "right," we could start doing that in
parallel with the refactoring work to off-the-shelf. But if we don't know
enough yet, then imo that's again an indication that we should start with
off-the-shelf.
Am I missing something?
> Make read and write requests paths fully non-blocking, eliminate related
> stages
> -------------------------------------------------------------------------------
>
> Key: CASSANDRA-10993
> URL: https://issues.apache.org/jira/browse/CASSANDRA-10993
> Project: Cassandra
> Issue Type: Sub-task
> Components: Coordination, Local Write-Read Paths
> Reporter: Aleksey Yeschenko
> Assignee: Tyler Hobbs
> Fix For: 3.x
>
> Attachments: 10993-reads-no-evloop-integration-six-node-stress.svg,
> tpc-benchmarks-2.txt, tpc-benchmarks.txt
>
>
> Building on work done by [~tjake] (CASSANDRA-10528), [~slebresne]
> (CASSANDRA-5239), and others, convert read and write request paths to be
> fully non-blocking, to enable the eventual transition from SEDA to TPC
> (CASSANDRA-10989)
> Eliminate {{MUTATION}}, {{COUNTER_MUTATION}}, {{VIEW_MUTATION}}, {{READ}},
> and {{READ_REPAIR}} stages, move read and write execution directly to Netty
> context.
> For lack of decent async I/O options on Linux, we’ll still have to retain an
> extra thread pool for serving read requests for data not residing in our page
> cache (CASSANDRA-5863), however.
> Implementation-wise, we only have two options available to us: explicit FSMs
> and chained futures. Fibers would be the third, and easiest option, but
> aren’t feasible in Java without resorting to direct bytecode manipulation
> (ourselves or using [quasar|https://github.com/puniverse/quasar]).
> I have seen 4 implementations bases on chained futures/promises now - three
> in Java and one in C++ - and I’m not convinced that it’s the optimal (or
> sane) choice for representing our complex logic - think 2i quorum read
> requests with timeouts at all levels, read repair (blocking and
> non-blocking), and speculative retries in the mix, {{SERIAL}} reads and
> writes.
> I’m currently leaning towards an implementation based on explicit FSMs, and
> intend to provide a prototype - soonish - for comparison with
> {{CompletableFuture}}-like variants.
> Either way the transition is a relatively boring straightforward refactoring.
> There are, however, some extension points on both write and read paths that
> we do not control:
> - authorisation implementations will have to be non-blocking. We have control
> over built-in ones, but for any custom implementation we will have to execute
> them in a separate thread pool
> - 2i hooks on the write path will need to be non-blocking
> - any trigger implementations will not be allowed to block
> - UDFs and UDAs
> We are further limited by API compatibility restrictions in the 3.x line,
> forbidding us to alter, or add any non-{{default}} interface methods to those
> extension points, so these pose a problem.
> Depending on logistics, expecting to get this done in time for 3.4 or 3.6
> feature release.
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