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https://issues.apache.org/jira/browse/CASSANDRA-6199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13855977#comment-13855977
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Benedict commented on CASSANDRA-6199:
-------------------------------------
That is a very bad reason to consider it the only correct usage. There is a
stronger reason to provide the return value, and that is linearizability. You
cannot be sure in many use cases of CHM.putIfAbsent that get() will return the
value you inserted, so some uses require it for actual correctness of function.
Since each key is immutable in our use case, this is not true, and we can do it
safely. Since there is a stronger reason to require the functionality, and
because in highly contended use cases there is a performance benefit, it is not
reasonable to assume that in situations where the stronger requirement is not
present and the performance is irrelevant that the functionality must be used.
Either way, I have agreed to the change, so I suggest we leave it there :-)
> Improve Stress Tool
> -------------------
>
> Key: CASSANDRA-6199
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6199
> Project: Cassandra
> Issue Type: Improvement
> Components: Tools
> Reporter: Benedict
> Assignee: Benedict
> Priority: Minor
> Attachments: new.read.latency.svg, new.read.rate.distribution.svg,
> new.write.latency.svg, new.write.rate.distribution.svg, old.read.latency.svg,
> old.read.rate.distribution.svg, old.write.latency.svg,
> old.write.rate.distribution.svg, ops.read.svg, ops.write.svg
>
>
> The stress tool could do with sprucing up. The following is a list of
> essential improvements and things that would be nice to have.
> Essential:
> - Reduce variability of results, especially start/end tails. Do not trash
> first/last 10% of readings
> - Reduce contention/overhead in stress to increase overall throughput
> - Short warm-up period, which is ignored for summary (or summarised
> separately), though prints progress as usual. Potentially automatic detection
> of rate levelling.
> - Better configurability and defaults for data generation - current column
> generation populates columns with the same value for every row, which is very
> easily compressible. Possibly introduce partial random data generator
> (possibly dictionary-based random data generator)
> Nice to have:
> - Calculate and print stdev and mean
> - Add batched sequential access mode (where a single thread performs
> batch-size sequential requests before selecting another random key) to test
> how key proximity affects performance
> - Auto-mode which attempts to establish the maximum throughput rate, by
> varying the thread count (or otherwise gating the number of parallel
> requests) for some period, then configures rate limit or thread count to test
> performance at e.g. 30%, 50%, 70%, 90%, 120%, 150% and unconstrained.
> - Auto-mode could have a target variance ratio for mean throughput and/or
> latency, and completes a test once this target is hit for x intervals
> - Fix key representation so independent of number of keys (possibly switch to
> 10 digit hex), and don't use String.format().getBytes() to construct it
> (expensive)
> Also, remove the skip-key setting, as it is currently ignored. Unless
> somebody knows the reason for it.
> - Fix latency stats
> - Read/write mode, with configurable recency-of-reads distribution
> - Add new exponential/extreme value distribution for value size, column count
> and recency-of-reads
> - Support more than 2^31 keys
> - Supports multiple concurrent stress inserts via key-offset parameter or
> similar
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