You are viewing a plain text version of this content. The canonical link for it is here.
Posted to commits@cassandra.apache.org by "Caleb Rackliffe (Jira)" <ji...@apache.org> on 2025/02/06 21:23:00 UTC
[jira] [Commented] (CASSANDRA-15452) Improve disk access patterns during compaction and range reads
[ https://issues.apache.org/jira/browse/CASSANDRA-15452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17924704#comment-17924704 ]
Caleb Rackliffe commented on CASSANDRA-15452:
---------------------------------------------
Had a Slack conversation about 4-5 minor items w/ [~jwest], but assuming those are buttoned up, +1
> Improve disk access patterns during compaction and range reads
> --------------------------------------------------------------
>
> Key: CASSANDRA-15452
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15452
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Legacy/Local Write-Read Paths, Local/Compaction
> Reporter: Jon Haddad
> Assignee: Jordan West
> Priority: Normal
> Fix For: 4.1.x, 5.0.x, 5.x
>
> Attachments: everyfs.txt, image-2024-11-22-16-17-23-194.png, image-2025-01-07-16-04-23-909.png, image-2025-01-07-16-56-12-853.png, image-2025-01-07-16-57-29-134.png, 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, screenshot-1.png, screenshot-2.png, screenshot-3.png, screenshot-4.png, screenshot-5.png, screenshot-6.png, sequential.fio, throughput-1.png, throughput.png
>
> Time Spent: 8.5h
> Remaining Estimate: 0h
>
> 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
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscribe@cassandra.apache.org
For additional commands, e-mail: commits-help@cassandra.apache.org