[jira] [Created] (HDFS-3120) Provide ability to enable sync without append

["Eli Collins (Created) (JIRA)" <ji...@apache.org>]

Provide ability to enable sync without append
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                 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.hsync* 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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