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From "Pavel Yaskevich (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-4718) More-efficient ExecutorService for improved throughput
Date Sat, 17 May 2014 16:41:17 GMT


Pavel Yaskevich commented on CASSANDRA-4718:

I think you have plotted numbers from May16. I'm not sure what do you mean by "often" the
problem with numbers is that they apparently cut off for both branches :( We have to redo
the test I think, [~jasobrown] is there a way to guarantee that both branches are going to
do the same number of runs with stress? I disagree with #2 because sep shows a sudden drop
at the end as do runs 1 and 3 so we don't really know what is going to happen with sep on
the high stress concurrency in those runs.

bq. This work is clearly disk bound as the same hardware was pushing 250k/s with similar record
sizes when exclusively in memory - we're seeing only 5% of that now. Unless possibly in-memory
index scans are occupying all of the time (but according to Jason CPU utilisation was around
30% from a random non-scientific poll).

I'm not sure if we can count 250K/s as a disk bound workload, which is only 3 buffer reads
per second. 

> More-efficient ExecutorService for improved throughput
> ------------------------------------------------------
>                 Key: CASSANDRA-4718
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Benedict
>            Priority: Minor
>              Labels: performance
>             Fix For: 2.1.0
>         Attachments: 4718-v1.patch,, austin_diskbound_read.svg, aws.svg,
aws_read.svg, backpressure-stress.out.txt, baq vs trunk.png, belliotsmith_branches-stress.out.txt,
jason_read.svg, jason_read_latency.svg, jason_run1.svg, jason_run2.svg, jason_run3.svg, jason_write.svg,
op costs of various queues.ods, stress op rate with various queues.ods, stress_2014May15.txt,
stress_2014May16.txt, v1-stress.out
> Currently all our execution stages dequeue tasks one at a time.  This can result in contention
between producers and consumers (although we do our best to minimize this by using LinkedBlockingQueue).
> One approach to mitigating this would be to make consumer threads do more work in "bulk"
instead of just one task per dequeue.  (Producer threads tend to be single-task oriented by
nature, so I don't see an equivalent opportunity there.)
> BlockingQueue has a drainTo(collection, int) method that would be perfect for this. 
However, no ExecutorService in the jdk supports using drainTo, nor could I google one.
> What I would like to do here is create just such a beast and wire it into (at least)
the write and read stages.  (Other possible candidates for such an optimization, such as the
CommitLog and OutboundTCPConnection, are not ExecutorService-based and will need to be one-offs.)
> AbstractExecutorService may be useful.  The implementations of ICommitLogExecutorService
may also be useful. (Despite the name these are not actual ExecutorServices, although they
share the most important properties of one.)

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