[
https://issues.apache.org/jira/browse/CASSANDRA-20176?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17942330#comment-17942330
]
Jon Haddad commented on CASSANDRA-20176:
----------------------------------------
Fwiw, I'm running a test now and seeing doWaitSpin taking up ~ 11% of CPU on a
very busy system. Most of the time is spent in LockSupport.parkNanos.
Flame graph attached.
> 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: flame-cassandra0-2025-04-09_23-56-13.html,
> 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/)
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
