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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