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Robert Stupp commented on CASSANDRA-11206:
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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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