Always flush HLog on root or meta region updates
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Key: HBASE-1148
URL: https://issues.apache.org/jira/browse/HBASE-1148
Project: Hadoop HBase
Issue Type: Bug
Components: regionserver
Affects Versions: 0.19.0, 0.19.1, 0.20.0
Reporter: Jim Kellerman
Assignee: Jim Kellerman
Priority: Critical
Flushing an HLog does not currently guarantee that the updates will be visible
(see HADOOP-4379), however in the case of root or meta region updates, this is
critical.
I was able to create a situation by killing both the root and meta region
servers, from which the cluster recovered, but because of the missed edits,
clients found the old parent region rather than the new child regions because
the fact that the parent region had split was not in the HLog of the crashed
region servers (the master knew because of the MSG_REGION_SPLIT message it
received) but the clients read the meta table and because that change was lost,
clients were trying to find the parent region.
So, when a SequenceFile.Writer.sync() guarantees that what has been written
will be visible to new readers, we need to modify HLog so that if it is writing
an update to the root or meta regions, that it immediately flushes (syncs) the
log file so that the changes will be visible when the log file is recovered.
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