In some particular deployments, the Replication code believes it has
reached EOF for a WAL prior to succesfully parsing all bytes known to
exist in a cleanly closed file.
Consistently this failure happens due to an InvalidProtobufException
after some number of seeks during our attempts to tail the in-progress
RegionServer WAL. As a work-around, this patch treats cleanly closed
files differently than other execution paths. If an EOF is detected due
to parsing or other errors while there are still unparsed bytes before
the end-of-file trailer, we now reset the WAL to the very beginning and
attempt a clean read-through.
In current testing, a single such reset is sufficient to work around
observed dataloss. However, the above change will retry a given WAL file
indefinitely. On each such attempt, a log message like the below will
be emitted at the WARN level:
Processing end of WAL file '{}'. At position {}, which is too far away
from reported file length {}. Restarting WAL reading (see HBASE-15983
for details).
Additionally, this patch adds some additional log detail at the TRACE
level about file offsets seen while handling recoverable errors. It also
add metrics that measure the use of this recovery mechanism.
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