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https://issues.apache.org/jira/browse/CASSANDRA-20173?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17947139#comment-17947139
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Dmitry Konstantinov commented on CASSANDRA-20173:
-------------------------------------------------
I have squashed the changes and rebased them on top of trunk:
[https://github.com/apache/cassandra/pull/4117]
Big Endian off-heap access logic needed for NativeAccessor is implemented using
the same approach as in CASSANDRA-20190
> Avoid new ByteBuffer allocation for each NativeCell/NativeClustering during
> flushing of offheap_objects memtable
> ----------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-20173
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20173
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Memtable
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Fix For: 5.x
>
> Attachments: image-2024-12-29-13-06-13-115.png,
> native_clustering_byte_buffer_alloc.png
>
> Time Spent: 3h 40m
> Remaining Estimate: 0h
>
> Currently for memtable_allocation_type: offheap_objects when we flush a
> memtable we allocate new ByteBuffer object for each NativeCell and
> NativeClustering to write it to disk. It is one of the main contributors
> (together with CASSANDRA-20162) to memory allocation for MemtableFlushWriter
> thread:
> !image-2024-12-29-13-06-13-115.png|width=570!
> !native_clustering_byte_buffer_alloc.png|width=570!
> Instead of retrieving of the value() as ByteBuffer we can introduce
> NativeValueAccessor to not expose ByteBuffer + keep it inside NativeCell as a
> thread-local to re-use. Same idea is applicable for NativeClustering
> Note: for Cassandra 4.x the situation is even worse because we clone very
> BTreeRow from off-heap to heap due to using the same iterator as for usual
> reads (where we need to protect against memtable lifecycle changes). In case
> of flushing such protection is not needed. For TrieMemtable we skip such
> cloning (CASSANDRA-17240,
> [https://github.com/apache/cassandra/blob/cassandra-5.0/src/java/org/apache/cassandra/db/memtable/TrieMemtable.java#L393]).
> It makes sense to consider such skipping for over types of memtable too..
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