[jira] [Commented] (HADOOP-16786) SequenceFile.Writer#hsync does not sync to disk when checksums are used

["Steve Loughran (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-16786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17007538#comment-17007538 ] 

Steve Loughran commented on HADOOP-16786:
-----------------------------------------

yeah, it's a known issue. I should make sure that the docs in HADOOP-13327 cover this "detail"

FWIW, calling hsync all the time has adverse consequences on HDFS, object stores etc. Only use it when you absolutely need to

> SequenceFile.Writer#hsync does not sync to disk when checksums are used
> -----------------------------------------------------------------------
>
>                 Key: HADOOP-16786
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16786
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Mathias Herberts
>            Priority: Major
>
> Recently I created a SequenceFile Writer and was surprised to see that the file size was not changing despite hsync being called after each append.
> After some fiddling around, I noticed that if write checksums are disabled then the hsync is effective.
> I checked the documentation and could not find any mention of the fact that hsync could be ineffective when write checksums are on.
> The Writer was using the LocalFilesystem.



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