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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-10993) Make read and write requests paths fully non-blocking, eliminate related stages
Date Wed, 03 Aug 2016 16:06:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15406130#comment-15406130
] 

Sylvain Lebresne commented on CASSANDRA-10993:
----------------------------------------------

I won't pretend having read very carefully neither this patch nor the one for RxJava but the
argument that with little proof of performance advantage we're better off leveraging and existing
and tested library, especially when the API is getting somewhat standardized, resonates with
me. I also share the gut feeling that the bulk of the wins is going to actually get to TPC
(or as close to it as we can) so we can simplify data structures (not only in term of performance,
but also in term of complexity required by these data structures), and re-using an existing
library sounds like it can get us there sooner without too much drawback.

> 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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