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From "Benedict (JIRA)" <>
Subject [jira] [Comment Edited] (CASSANDRA-7282) Faster Memtable map
Date Thu, 21 Aug 2014 01:55:45 GMT


Benedict edited comment on CASSANDRA-7282 at 8/21/14 1:55 AM:

memtable_heap_space_in_mb: 4096
memtable_offheap_space_in_mb: 2048
-Xm[xn]8Gb (or more)

Looks like the top two settings were missing from the yaml somehow. Ninja'd them in.

was (Author: benedict):
memtable_heap_space_in_mb: 4096
memtable_offheap_space_in_mb: 2048

> Faster Memtable map
> -------------------
>                 Key: CASSANDRA-7282
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>              Labels: performance
>             Fix For: 3.0
> 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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