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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6199) Improve Stress Tool
Date Mon, 14 Oct 2013 22:49:41 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13794591#comment-13794591
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Benedict commented on CASSANDRA-6199:
-------------------------------------

The short warm-up period is meant to take the place of the current arbitrary imposition of
dropping the first 10% of all results. Often this is much more than needs to be ignored, especially
for large tests, so it should at least be an improvement from what we currently have.

As to affecting the post warm-up phase, this is true for writes, but I would note again both
that this change should reduce the problem, and that whilst it is fairly difficult to avoid
the problem entirely, assuming a constant rate of stress any latent effects should reach a
steady state at some point - hence the idea of an auto mode, which attempts to establish the
steady state and report this, as opposed to running for n iterations. If analysing a graph
of the results for n iterations any warm-up period would be included anyway, and could be
understood, as is currently the case.

bq. FBUtilities has an implementation, incidentally.

In this case simple creating a Random in each thread should be the easiest solution, thread
local isn't really helpful here.

> 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
>
> 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.
> - Per thread Random
> 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
> Also, remove the skip-key setting, as it is currently ignored. Unless somebody knows
the reason for it.



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