C. Scott Andreas created CASSANDRA-21285:
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Summary: Reduce allocations + copies due to rebuffering in
LocalDataResponse row serialization
Key: CASSANDRA-21285
URL: https://issues.apache.org/jira/browse/CASSANDRA-21285
Project: Apache Cassandra
Issue Type: Task
Components: Messaging/Client
Reporter: C. Scott Andreas
Attachments: CASSANDRA-21285.diff, after.png, before.png
This patch reduces allocations due to rebuffering in LocalDataResponse row
serialization.
Today, LocalDataResponse#build serializes row responses without providing a
size estimate when initializing a DataOutputBuffer. Read responses that exceed
the initial size of 128 bytes incur progressive size doubling, allocation, and
buffer copying until the result fits.
This patch maintains a lightweight moving average of read response sizes and
uses this to size the initial response.
In a read-heavy workload dominated by resultset paging, this change reduces
memory allocations/copies by about 9%. [1]
The change is most visible in the Native-Transport-Requests threadpool.
*Trunk:*
{{Thread Pool Threads Allocated
Count % of Total}}
{{----------------------------------------------------------------------------------------------------}}
{{Native-Transport-Requests 10 68.45 GiB
348,724 74.02%}}
*Trunk + Patch:*
{{Thread Pool Threads Allocated
Count % of Total}}
{{----------------------------------------------------------------------------------------------------}}
{{Native-Transport-Requests 11 62.52 GiB
324,523 74.13%}}
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[1] Workload example:
[https://gist.github.com/cscotta/580378387c73b49822f287910771d14f]
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