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https://issues.apache.org/jira/browse/CASSANDRA-21683?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jon Haddad updated CASSANDRA-21683:
-----------------------------------
Description:
When Cassandra writes a BTI SSTable, it builds a partition index: a trie that
maps each partition key to its position on disk. To place a key in the trie,
the builder first converts it to a byte-comparable form, a byte string that
sorts in the same order as the key.
That conversion runs repeatedly. For each partition, the builder re-encodes the
same one or two keys about four times: once to find where a key differs from
its neighbour, once to cut the shared prefix, and again when the trie re-reads
the previous key. Each encode allocates a chain of throwaway objects
(ByteSource, Multi, varargs arrays, escapers), roughly nineteen short-lived
objects per partition. Across a flush or compaction with millions of
partitions, this is a large amount of garbage, and it pressures the garbage
collector
was:Placeholder...
> Reduce allocations in BTI writes
> --------------------------------
>
> Key: CASSANDRA-21683
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21683
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/SSTable
> Reporter: Jon Haddad
> Assignee: Jon Haddad
> Priority: Normal
>
> When Cassandra writes a BTI SSTable, it builds a partition index: a trie that
> maps each partition key to its position on disk. To place a key in the trie,
> the builder first converts it to a byte-comparable form, a byte string that
> sorts in the same order as the key.
> That conversion runs repeatedly. For each partition, the builder re-encodes
> the same one or two keys about four times: once to find where a key differs
> from its neighbour, once to cut the shared prefix, and again when the trie
> re-reads the previous key. Each encode allocates a chain of throwaway objects
> (ByteSource, Multi, varargs arrays, escapers), roughly nineteen short-lived
> objects per partition. Across a flush or compaction with millions of
> partitions, this is a large amount of garbage, and it pressures the garbage
> collector
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