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https://issues.apache.org/jira/browse/HDFS-15567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17193230#comment-17193230
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Konstantin Shvachko commented on HDFS-15567:
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Here are some options to start the discussion:
# A straightforward way is to just add {{msync()}} to {{FileSystem}} with the
default implementation as unsupported operation. This is similar to snapshot or
extended attributes operations, which have meaningful implementation only for
HDFS-based file systems: {{WebHdfsFileSystem}}, {{ViewFileSystem}}.
# Add {{DistributedFileSystem.msync()}}, but not {{FileSystem}}. {{msync()}}
is specific to HDFS, although both WebHDFS and ViewFS can benefit from it.
# Expose {{msync()}} via some utility class like {{HAUtil}}. In the end it is
an HA feature.
# Do nothing - calling {{msync()}} via DFSClient is good enough.
> [SBN Read] HDFS should expose msync() API to allow downstream applications
> call it explicetly.
> ----------------------------------------------------------------------------------------------
>
> Key: HDFS-15567
> URL: https://issues.apache.org/jira/browse/HDFS-15567
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: ha, hdfs-client
> Reporter: Konstantin Shvachko
> Priority: Major
>
> Consistent reads from Standby introduced {{msync()}} API HDFS-13688, which
> updates client's state ID with current state of the Active NameNode to
> guarantee consistency of subsequent calls to an ObserverNode. Currently this
> API is exposed via {{DFSClient}} only, which makes it hard for applications
> to access {{msync()}}. One way is to use something like this:
> {code}
> if(fs instanceof DistributedFileSystem) {
> ((DistributedFileSystem)fs).getClient().msync();
> }
> {code}
> This should be exposed both for {{FileSystem}} and {{FileContext}}.
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