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https://issues.apache.org/jira/browse/CASSANDRA-15452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17846740#comment-17846740
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Jon Haddad commented on CASSANDRA-15452:
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Jordan and I did some additional testing today and were able to get about 8x
improvement to compaction throughput while running a write heavy workload. We
actually hit the EBS throughput limit instead of the IOPS limit and scaled the
volume up to see where it caps out. The green line is the node with the patch,
the other nodes are the head of 5.0.
!throughput.png!
> Improve disk access patterns during compaction and streaming
> ------------------------------------------------------------
>
> Key: CASSANDRA-15452
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15452
> Project: Cassandra
> Issue Type: Improvement
> Components: Legacy/Local Write-Read Paths, Local/Compaction
> Reporter: Jon Haddad
> Assignee: Jordan West
> Priority: Normal
> Attachments: everyfs.txt, iostat-5.0-head.output,
> iostat-5.0-patched.output, iostat-ebs-15452.png, iostat-ebs-head.png,
> iostat-instance-15452.png, iostat-instance-head.png, results.txt,
> sequential.fio, throughput-1.png, throughput.png
>
>
> On read heavy workloads Cassandra performs much better when using a low read
> ahead setting. In my tests I've seen an 5x improvement in throughput and
> more than a 50% reduction in latency. However, I've also observed that it
> can have a negative impact on compaction and streaming throughput. It
> especially negatively impacts cloud environments where small reads incur high
> costs in IOPS due to tiny requests.
> # We should investigate using POSIX_FADV_DONTNEED on files we're compacting
> to see if we can improve performance and reduce page faults.
> # This should be combined with an internal read ahead style buffer that
> Cassandra manages, similar to a BufferedInputStream but with our own
> machinery. This buffer should read fairly large blocks of data off disk at
> at time. EBS, for example, allows 1 IOP to be up to 256KB. A considerable
> amount of time is spent in blocking I/O during compaction and streaming.
> Reducing the frequency we read from disk should speed up all sequential I/O
> operations.
> # We can reduce system calls by buffering writes as well, but I think it
> will have less of an impact than the reads
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