[jira] [Commented] (CASSANDRA-14466) Enable Direct I/O

["Ariel Weisberg (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-14466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16489366#comment-16489366 ] 

Ariel Weisberg commented on CASSANDRA-14466:
--------------------------------------------

How does this work with early open where the file is currently being written with buffered IO? I thought buffered IO and direct IO shouldn't be mixed on the same file?

Also what hardware were you testing on? What benchmark did you run? Was this running with or without compression?

I've got to say it's a little surprising that reading from RAM is slower than reading from an ordinary SATA or NVMe flash device. Can you explain that result? Was this a completely uncachable read workload?

> Enable Direct I/O 
> ------------------
>
>                 Key: CASSANDRA-14466
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14466
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Local Write-Read Paths
>            Reporter: Mulugeta Mammo
>            Priority: Major
>         Attachments: direct_io.patch
>
>
> Hi,
> JDK 10 introduced a new API for Direct IO that enables applications to bypass the file system cache and potentially improve performance. Details of this feature can be found at [https://bugs.openjdk.java.net/browse/JDK-8164900].
> This patch uses the JDK 10 API to enable Direct IO for the Cassandra read path. By default, we have disabled this feature; but it can be enabled using a  new configuration parameter, enable_direct_io_for_read_path. We have conducted a Cassandra read-only stress test and measured a throughput gain of up to 60% on flash drives.
> The patch requires JDK 10 Cassandra Support - https://issues.apache.org/jira/browse/CASSANDRA-9608 
> Please review the patch and let us know your feedback.
> Thanks,
> [^direct_io.patch]
>  



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