[
https://issues.apache.org/jira/browse/CASSANDRA-8915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14528503#comment-14528503
]
Benedict commented on CASSANDRA-8915:
-------------------------------------
My mistake, I thought I linked it. My version with updated tests and
optimization is
[here|https://github.com/belliottsmith/cassandra/tree/mergeiterator-comparison]
That sounds like a much simpler solution; if we can get even 50% of the benefit
with that approach I'm happy. I'll take a look shortly
> Improve MergeIterator performance
> ---------------------------------
>
> Key: CASSANDRA-8915
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8915
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Branimir Lambov
> Assignee: Branimir Lambov
> Priority: Minor
> Fix For: 3.x
>
>
> The implementation of {{MergeIterator}} uses a priority queue and applies a
> pair of {{poll}}+{{add}} operations for every item in the resulting sequence.
> This is quite inefficient as {{poll}} necessarily applies at least {{log N}}
> comparisons (up to {{2log N}}), and {{add}} often requires another {{log N}},
> for example in the case where the inputs largely don't overlap (where {{N}}
> is the number of iterators being merged).
> This can easily be replaced with a simple custom structure that can perform
> replacement of the top of the queue in a single step, which will very often
> complete after a couple of comparisons and in the worst case scenarios will
> match the complexity of the current implementation.
> This should significantly improve merge performance for iterators with
> limited overlap (e.g. levelled compaction).
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
