[jira] [Updated] (CASSANDRA-10993) Make read and write requests paths fully non-blocking, eliminate related stages

["Tyler Hobbs (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-10993?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tyler Hobbs updated CASSANDRA-10993:
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    Attachment: 10993-reads-no-evloop-integration-six-node-stress.svg

I finally got a proper setup for recording some flamegraphs of the current 10993 branch during reads.  The attached image was recorded while six stress processed read from a single C* node.  All of the reads were served from a memtable.

In short, it looks like we spend very little time dealing with the netty task queue when the node is actually saturated with reads (roughly ~1%).  Previous flamegraphs were misleading, because a single stress client was not enough to saturate the node, so a higher percentage of time was spent in the event loops waiting for tasks.

Based on this data, I'm not sure that it makes sense to focus on creating a custom Netty event loop for more efficient integration.  So, I plan to move onto benchmarking in-memory reads with the current 10993 vs trunk (at least, the common ancestor of trunk and 10993) vs CASSANDRA-10528 (ported to the same trunk ancestor).

> 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
>
>
> 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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