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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9486) LazilyCompactedRow accumulates all expired RangeTombstones
Date Tue, 02 Jun 2015 14:40:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14569175#comment-14569175
] 

Sylvain Lebresne commented on CASSANDRA-9486:
---------------------------------------------

I had actually forgot one "add" in {{update}} which was breaking tests. I've pushed the fix
and I'll wait once the tests have ran.

bq. the semantics of an arbitrary method labelled insertBefore might well want to do so

Right, felt more logical so makes hypothetical future misuse of the method less likely.

> LazilyCompactedRow accumulates all expired RangeTombstones
> ----------------------------------------------------------
>
>                 Key: CASSANDRA-9486
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9486
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Sylvain Lebresne
>            Priority: Critical
>             Fix For: 3.x, 2.1.x, 2.0.x, 2.2.x, 1.2.x
>
>         Attachments: 0001-9486.patch
>
>
> LazilyCompactedRow initializes a ColumnIndex.Builder to use its RangeTombstone.Tracker,
but it only calls update() with a RT argument, never an atom. The Tracker only ever _adds_
if it receives a RT, never removes. So all the RT ever seen for the partition (that have expired)
remain in memory until the compaction completes. To make matters worse, this then forces a
linear scan of all of these RT for each live cell we add, so this extra load hangs around
for a long time, and compactions stall.
> This issue is biting one of our users badly (at least, it seems likely to be this issue),
and there may be others. This user is not even making use of RT extensively themselves, only
collections (presumably with a complete overwrite of the contents of the collection, resulting
in a RT being generated).
> Probably the best solution is to make the RT addition itself remove any already present
that are no longer helpful.



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