Dmitry Konstantinov created CASSANDRA-20176:
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Summary: 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
Attachments: image-2025-01-01-13-14-02-562.png,
image-2025-01-01-13-15-16-767.png
There is a quite massive 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 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 a thread
is needed 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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