[jira] [Updated] (CASSANDRA-7282) Faster Memtable map

["C. Scott Andreas (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

C. Scott Andreas updated CASSANDRA-7282:
----------------------------------------
    Component/s: Local Write-Read Paths

> Faster Memtable map
> -------------------
>
>                 Key: CASSANDRA-7282
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7282
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local Write-Read Paths
>            Reporter: Benedict
>            Assignee: Michael Burman
>            Priority: Major
>              Labels: performance
>             Fix For: 4.x
>
>         Attachments: jasobrown-sample-run.txt, profile.yaml, reads.svg, run1.svg, writes.svg
>
>
> Currently we maintain a ConcurrentSkipLastMap of DecoratedKey -> Partition in our memtables. Maintaining this is an O(lg(n)) operation; since the vast majority of users use a hash partitioner, it occurs to me we could maintain a hybrid ordered list / hash map. The list would impose the normal order on the collection, but a hash index would live alongside as part of the same data structure, simply mapping into the list and permitting O(1) lookups and inserts.
> I've chosen to implement this initial version as a linked-list node per item, but we can optimise this in future by storing fatter nodes that permit a cache-line's worth of hashes to be checked at once,  further reducing the constant factor costs for lookups.



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