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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11206) Support large partitions on the 3.0 sstable format
Date Thu, 14 Apr 2016 21:08:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15241925#comment-15241925
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T Jake Luciani commented on CASSANDRA-11206:
--------------------------------------------

* You need to change the version of sstable since this change alters the Index component.
* Please run dtests/unit test with column_index_cache_size_in_kb: 0 
* Is the AutoSavingCache change require a step on the users part or will it naturally skip
the saved cache on startup?
* The 0,1,2 magic bytes that encode what type of index entry this is should be made constants

> Support large partitions on the 3.0 sstable format
> --------------------------------------------------
>
>                 Key: CASSANDRA-11206
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11206
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Robert Stupp
>             Fix For: 3.x
>
>         Attachments: 11206-gc.png, trunk-gc.png
>
>
> Cassandra saves a sample of IndexInfo objects that store the offset within each partition
of every 64KB (by default) range of rows.  To find a row, we binary search this sample, then
scan the partition of the appropriate range.
> The problem is that this scales poorly as partitions grow: on a cache miss, we deserialize
the entire set of IndexInfo, which both creates a lot of GC overhead (as noted in CASSANDRA-9754)
but is also non-negligible i/o activity (relative to reading a single 64KB row range) as partitions
get truly large.
> We introduced an "offset map" in CASSANDRA-10314 that allows us to perform the IndexInfo
bsearch while only deserializing IndexInfo that we need to compare against, i.e. log(N) deserializations.



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