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From "Dominic Letz (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-8546) RangeTombstoneList becoming bottleneck on tombstone heavy tasks
Date Tue, 06 Jan 2015 02:21:34 GMT


Dominic Letz commented on CASSANDRA-8546:

This makes all sense. From my reading it also appeared that the way the RangeTombstoneList
is used in reads vs. in compaction and other places is actually so different that it could
use  different use case optimized data-structures in different places rather than re-using
the RangeTombstoneList. CASSANDRA-8099 might be an opportunity to change that.

Until then though the GapList change could be a minimal impact fix. It does not change the
structure of the code and does not regress the read path while fixing the reverse read issue
and giving linear speedups:
- Read in forward stays as is.
- Read in reverse moves from O(n) to O(1)
- grow() becomes 4x faster since there is only one array to grow
- insertFrom becomes at least 8x faster (only one array to shift instead of four , and in
worst case only every second insert) 

Obviously I'm scratching here my own itch to improve reverse reads and compaction with tombstone
heavy workloads - is there any way I can help make that happen for 2.1 ?

> RangeTombstoneList becoming bottleneck on tombstone heavy tasks
> ---------------------------------------------------------------
>                 Key: CASSANDRA-8546
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>         Environment: 2.0.11 / 2.1
>            Reporter: Dominic Letz
>            Assignee: Benedict
>             Fix For: 2.1.3
>         Attachments: cassandra-2.0.11-8546.txt, cassandra-2.1-8546.txt, tombstone_test.tgz
> I would like to propose a change of the data structure used in the RangeTombstoneList
to store and insert tombstone ranges to something with at least O(log N) insert in the middle
and at near O(1) and start AND end. Here is why:
> When having tombstone heavy work-loads the current implementation of RangeTombstoneList
becomes a bottleneck with slice queries.
> Scanning the number of tombstones up to the default maximum (100k) can take up to 3 minutes
of how addInternal() scales on insertion of middle and start elements.
> The attached test shows that with 50k deletes from both sides of a range.
> INSERT 1...110000
> flush()
> DELETE 1...50000
> DELETE 110000...60000
> While one direction performs ok (~400ms on my notebook):
> {code}
> SELECT * FROM timeseries WHERE name = 'a' ORDER BY timestamp DESC LIMIT 1
> {code}
> The other direction underperforms (~7seconds on my notebook)
> {code}
> SELECT * FROM timeseries WHERE name = 'a' ORDER BY timestamp ASC LIMIT 1
> {code}

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