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https://issues.apache.org/jira/browse/CASSANDRA-18464?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Josh McKenzie reassigned CASSANDRA-18464:
-----------------------------------------
Assignee: Amit Pawar
> Enable Direct I/O For CommitLog Files
> -------------------------------------
>
> Key: CASSANDRA-18464
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18464
> Project: Cassandra
> Issue Type: New Feature
> Components: Local/Commit Log
> Reporter: Josh McKenzie
> Assignee: Amit Pawar
> Priority: Normal
> Fix For: 6.x
>
> Attachments: UseDirectIOFeatureForCommitLogFiles.patch
>
>
> Relocating from [dev@ email
> thread.|https://lists.apache.org/thread/j6ny17q2rhkp7jxvwxm69dd6v1dozjrg]
>
> I shared my investigation about Commitlog I/O issue on large core count
> system in my previous email dated July-22 and link to the thread is given
> below.
> [https://lists.apache.org/thread/xc5ocog2qz2v2gnj4xlw5hbthfqytx2n]
> Basically, two solutions looked possible to improve the CommitLog I/O.
> # Multi-threaded syncing
> # Using Direct-IO through JNA
> I worked on 2nd option considering the following benefit compared to the
> first one
> # Direct I/O read/write throughput is very high compared to non-Direct I/O.
> Learnt through FIO benchmarking.
> # Reduces kernel file cache uses which in-turn reduces kernel I/O activity
> for Commitlog files only.
> # Overall CPU usage reduced for flush activity. JVisualvm shows CPU usage <
> 30% for Commitlog syncer thread with Direct I/O feature
> # Direct I/O implementation is easier compared to multi-threaded
> As per the community suggestion, less in code complex is good to have. Direct
> I/O enablement looked promising but there was one issue.
> Java version 8 does not have native support to enable Direct I/O. So, JNA
> library usage is must. The same implementation should also work across other
> versions of Java (like 11 and beyond).
> I have completed Direct I/O implementation and summary of the attached patch
> changes are given below.
> # This implementation is not using Java file channels and file is opened
> through JNA to use Direct I/O feature.
> # New Segment are defined named “DirectIOSegment” for Direct I/O and
> “NonDirectIOSegment” for non-direct I/O (NonDirectIOSegment is test purpose
> only).
> # JNA write call is used to flush the changes.
> # New helper functions are defined in NativeLibrary.java and platform
> specific file. Currently tested on Linux only.
> # Patch allows user to configure optimum block size and alignment if
> default values are not OK for CommitLog disk.
> # Following configuration options are provided in Cassandra.yaml file
> a. use_jna_for_commitlog_io : to use jna feature
> b. use_direct_io_for_commitlog : to use Direct I/O feature.
> c. direct_io_minimum_block_alignment: 512 (default)
> d. nvme_disk_block_size: 32MiB (default and can be changed as per the
> required size)
> Test matrix is complex so CommitLog related testcases and TPCx-IOT benchmark
> was tested. It works with both Java 8 and 11 versions. Compressed and
> Encrypted based segments are not supported yet and it can be enabled later
> based on the Community feedback.
> Following improvement are seen with Direct I/O enablement.
> # 32 cores >= ~15%
> # 64 cores >= ~80%
> Also, another observation would like to share here. Reading Commitlog files
> with Direct I/O might help in reducing node bring-up time after the node
> crash.
> Tested with commit ID: 91f6a9aca8d3c22a03e68aa901a0b154d960ab07
> The attached patch enables Direct I/O feature for Commitlog files. Please
> check and share your feedback.
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