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https://issues.apache.org/jira/browse/CASSANDRA-4860?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632991#comment-13632991
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Jonathan Ellis commented on CASSANDRA-4860:
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bq. 2M KV with Measure.measure() will take 96,000,000 or 96M (2 *24 * 2000000
bytes) will fit in key cache.
b1. 2M KV with measureDeep() will take 96M + 48M (48 * 2000000 + 24 * 2000000)
where 48 is the index min size and 24 is the key size.
Clarifying for my own benefit: Vijay is saying that before the original fix,
the key cache underestimated the real entry size by 1/3, so a configured size
of 2M would actually allow caching 3M worth of entries. So to compare
performance apples-to-apples, we need to allow the fixed code to use an
equivalent size.
> Estimated Row Cache Entry size incorrect (always 24?)
> -----------------------------------------------------
>
> Key: CASSANDRA-4860
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4860
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.1.0, 1.2.3, 2.0
> Reporter: Chris Burroughs
> Assignee: Vijay
> Fix For: 1.2.0 beta 3
>
> Attachments: 0001-4860-v2.patch, 0001-4860-v3.patch,
> 0001-CASSANDRA-4860-for-11.patch, 0001-CASSANDRA-4860.patch,
> 4860-perf-test.zip, trunk-4860-revert.patch
>
>
> After running for several hours the RowCacheSize was suspicious low (ie 70
> something MB) I used CASSANDRA-4859 to measure the size and number of
> entries on a node:
> In [3]: 1560504./65021
> Out[3]: 24.0
> In [4]: 2149464./89561
> Out[4]: 24.0
> In [6]: 7216096./300785
> Out[6]: 23.990877204647838
> That's RowCacheSize/RowCacheNumEntires . Just to prove I don't have crazy
> small rows the mean size of the row *keys* in the saved cache is 67 and
> Compacted row mean size: 355. No jamm errors in the log
> Config notes:
> row_cache_provider: ConcurrentLinkedHashCacheProvider
> row_cache_size_in_mb: 2048
> Version info:
> * C*: 1.1.6
> * centos 2.6.32-220.13.1.el6.x86_64
> * java 6u31 Java HotSpot(TM) 64-Bit Server VM (build 20.6-b01, mixed mode)
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