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https://issues.apache.org/jira/browse/CASSANDRA-21354?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dmitry Konstantinov updated CASSANDRA-21354:
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Summary: Avoid serialization and deserialization for coordinator-local
single partition data read (was: Avoid serialization and deserialization for
coordnator local single partition data read)
> Avoid serialization and deserialization for coordinator-local single
> partition data read
> ----------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21354
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21354
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Other
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Fix For: 6.x, 7.x
>
> Attachments: image-2026-05-07-10-10-16-886.png, may3_max_alloc.html
>
>
> Currently when we execute a local read we fetch data from SSTables and
> Memtables using a merging iterator and write it to a byte buffer. Later when
> we combine a CQL response we deserialize the data back to iterate over them
> as a part of coordinator logic. So, we allocate rows and cells twice here,
> during the read from SSTables/Memtables and during the deserialization by
> coordinator logic if we read data locally (it is a typical scenario because
> usually drivers are sending requests to replicas).
> The idea of optimization: if we do a single partition read of a small number
> of rows we can keep the data in memory and avoid this double row objects
> allocation.
> We should limit amount of such data kept in memory to avoid too much pressure
> on GC due to extended lifetime for these objects and promoting them to an old
> generation.
> So, a system property can be used to limit number of rows we keep in memory
> in this scenario, as well as to disable the logic in case of any issues.
> !image-2026-05-07-10-10-16-886.png|width=800!
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