Jeffrey Zhong created HBASE-8208:
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Summary: Data could not be replicated to slaves when
deferredLogSync is enabled
Key: HBASE-8208
URL: https://issues.apache.org/jira/browse/HBASE-8208
Project: HBase
Issue Type: Bug
Affects Versions: 0.94.6, 0.95.0, 0.98.0
Reporter: Jeffrey Zhong
This is a subtle issue. When deferredLogSync is enabled, there are chances we
could flush data before syncing all HLog entries. Assuming we just flush the
internal cache and the server dies with some unsynced hlog entries.
Data is not lost at the source cluster while replication is based on WAL files
and some changes we flushed at the source won't be replicated the slave
clusters.
Although enabling deferredLogSync with tolerances of data loss, it breaks the
replication assumption that whatever persisted in the source should be
replicated to its slave clusters.
In short, the slave cluster could end up with double losses: the data loss in
the source and some data stored in source cluster may not be replicated to
slaves either.
The fix of the issue isn't hard. Basically we can invoke sync during each flush
when replication is enabled for a region server. Since sync returns immediately
when nothing to sync so there should be no performance impact.
Please let me know what you think!
Thanks,
-Jeffrey
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