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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15051) FSDataOutputStream returned by LocalFileSystem#createNonRecursive doesn't have hflush capability
Date Sun, 19 Nov 2017 11:01:06 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16258442#comment-16258442

Steve Loughran commented on HADOOP-15051:

that's because it doesn't hflush. it's a checksummed output stream and it doesn't write until
it's got enough to checksum, or you reach the EOF. It has been like this for a very long time.

See HADOOP-13327 for adding the capability declarations to the output streams, with tests.
This will allow local FS to make absolutely clear that local FS doesn't do hflush/hsync.

> FSDataOutputStream returned by LocalFileSystem#createNonRecursive doesn't have hflush
> ------------------------------------------------------------------------------------------------
>                 Key: HADOOP-15051
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15051
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: fs
>    Affects Versions: 3.0.0-beta1
>            Reporter: Ted Yu
> See HBASE-19289 for background information.
> Here is related hbase code (fs is instance of LocalFileSystem):
> {code}
>     this.output = fs.createNonRecursive(path, overwritable, bufferSize, replication,
>       null);
>     // TODO Be sure to add a check for hsync if this branch includes HBASE-19024
>     if (!(CommonFSUtils.hasCapability(output, "hflush"))) {
>       throw new StreamLacksCapabilityException("hflush");
> {code}
> StreamCapabilities is used to poll "hflush" capability.
> [~busbey] suggested fixing this in hadoop.

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