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https://issues.apache.org/jira/browse/HDFS-3120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13241465#comment-13241465
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Eli Collins commented on HDFS-3120:
-----------------------------------
Forgot to mention, given that we know there are data loss issues with append,
why don't we remove the ability to enable it at the same time? It's an
incompatible change, however there's also no reason in letting users shoot
themselves in the foot.
> Provide ability to enable sync without append
> ---------------------------------------------
>
> Key: HDFS-3120
> URL: https://issues.apache.org/jira/browse/HDFS-3120
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 1.0.1
> Reporter: Eli Collins
> Assignee: Eli Collins
>
> The work on branch-20-append was to support *sync*, for durable HBase WALs,
> not *append*. The branch-20-append implementation is known to be buggy.
> There's been confusion about this, we often answer queries on the list [like
> this|http://search-hadoop.com/m/wfed01VOIJ5]. Unfortunately, the way to
> enable correct sync on branch-1 for HBase is to set dfs.support.append to
> true in your config, which has the side effect of enabling append (which we
> don't want to do).
> Let's add a new *dfs.support.sync* option that enables working sync (which is
> basically the current dfs.support.append flag modulo one place where it's not
> referring to sync). For compatibility, if dfs.support.append is set,
> dfs.support.sync will be set as well. This way someone can enable sync for
> HBase and still keep the current behavior that if dfs.support.append is not
> set then an append operation will result in an IOE indicating append is not
> supported. We should do this on trunk as well, as there's no reason to
> conflate hsync and append with a single config even if append works.
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