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From "Robert Stupp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11206) Support large partitions on the 3.0 sstable format
Date Fri, 15 Apr 2016 18:22:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15243356#comment-15243356
] 

Robert Stupp commented on CASSANDRA-11206:
------------------------------------------

Pushed another commit for the metrics. Intention of the metrics is to find the _sweet spot_
of {{column_index_cache_size_in_kb}}. In order to find that _sweet spot_ you need to know
the size of the entries. The metrics below {{org.apache.cassandra.metrics:type=Index,name=RowIndexEntry}}
are updated on each call to {{openWithIndex}}. But again, configuring {{column_index_cache_size_in_kb}}
too high would result in GC pressure and probably in a bad key cache hit ratio.
* {{IndexedEntrySize}} histogram about the side of IndexedEntry (every type)
* {{IndexInfoCount}} histogram about the number of IndexInfo objects per IndexedEntry (every
type)
* {{IndexInfoGets}} histogram about the number of gets of a IndexInfo objects per IndexedEntry
(every type) (for example the number of gets for a binary search)


> 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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