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Chris Lohfink commented on CASSANDRA-21550:
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Adding [https://github.com/apache/cassandra/pull/5015] as a 4.1 branch for
anticompaction only
Note on PR size: 78% documentation and tests
> Zero-copy sstable splitting for anticompaction, and partial-sstable zero-copy
> streaming
> ---------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21550
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21550
> Project: Apache Cassandra
> Issue Type: New Feature
> Reporter: Chris Lohfink
> Priority: Normal
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Anticompaction and range streaming both spend most of their cost re-doing
> work whose result they already have on disk. Anticompaction rewrites every
> row of an sstable through three writers only to place each partition into a
> repaired, transient or unrepaired child. Streaming a subset of an sstable's
> ranges takes the row-by-row path, where the sender is cheap (whole
> compression chunks are sent verbatim) but the receiver decompresses,
> deserialises, re-serialises and recompresses every row and then rebuilds the
> index, filter and summary it could have been handed. Both are avoidable when
> the bytes wanted are a contiguous run of the parent's compression chunks: the
> chunks can be copied (or extent-shared) verbatim and every other component
> rebuilt from an index-only pass, with no row deserialised on either side.
> This adds that machinery and the two callers for it. Both are off by default.
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