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https://issues.apache.org/jira/browse/CASSANDRA-20176?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17915797#comment-17915797
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Josh McKenzie commented on CASSANDRA-20176:
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Not sure how much time and appetite you have for experimentation, but I'd be
very interested to see the non-SEP executor running on virtual threads in JDK22
(since prior have a synchronized deadlock limitation with vthreads). We have a
ticket w/JDK21 support in CASSANDRA-18831; I expect the JDK21-JDK22 support
delta wouldn't be large at all. build.xml and startup script changes most
likely. [~edimitrova] did some prototyping on JDK22 if I'm not mistaken.
Anyway - just in case any of the above is interesting to you, figured I'd point
it out. Super interesting work here.
> Reduce memory allocation in SEP Worker spin wait logic
> ------------------------------------------------------
>
> Key: CASSANDRA-20176
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20176
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Other
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Attachments: image-2025-01-01-13-14-02-562.png,
> image-2025-01-01-13-15-16-767.png, ttop_disabled_sep.txt, ttop_enabled_sep.txt
>
>
> There is a visible memory allocation within spin waiting logic in SEP
> Executor: org.apache.cassandra.concurrent.SEPWorker#doWaitSpin for some
> workloads. For example it is observed for a writing test described in
> CASSANDRA-20165 where ~8.5% of total allocations are from this logic:
> !image-2025-01-01-13-14-02-562.png|width=570!
> !image-2025-01-01-13-15-16-767.png|width=570!
> The idea of this parking is to avoid unpark signalling costs. The logic
> selects a random time period to park a thread by LockSupport.parkNanos and
> put the thread into a ConcurrentSkipListMap using wake up time as a key, so
> the map is used as a concurrent priority queue. Once the parking is finished
> - the thread removes itself from the map. When we neede to schedule a task -
> we take a spinning thread with the smallest wake up time from the map.
> We can try to implement another algorithm for this logic without memory
> allocation overheads, for example based on a Timing Wheel data structure.
> Note: it also makes sense to check granularity of actual parking time
> (https://hazelcast.com/blog/locksupport-parknanos-under-the-hood-and-the-curious-case-of-parking/)
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