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From "Clint Morgan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1880) DeleteColumns are not recovered properly from the write-ahead-log
Date Thu, 01 Oct 2009 22:50:23 GMT
DeleteColumns are not recovered properly from the write-ahead-log

                 Key: HBASE-1880
                 URL: https://issues.apache.org/jira/browse/HBASE-1880
             Project: Hadoop HBase
          Issue Type: Bug
          Components: regionserver
    Affects Versions: 0.20.0, 0.20.1, 0.21.0
            Reporter: Clint Morgan
            Priority: Critical

I found a couple of issues:
 - The timestamp is being set to now after it has been written to the wal. So if the WAL was
flushed on that write, it gets in with ts of MAX_INT and is effectively lost.

 - Even after that fix, I had issues getting the delete to apply properly. In my case, the
WAL had a put to a column, then a DeleteColumn for the same column. The DeleteColumn KV had
a later timestamp, but it was still lost on recovery. I traced around a bit, and it looks
like the current approach of just using an HFile.writer to write the set of KVs read from
the log will not work. There is special logic in MemStore for deletes that needs to happen
before writing. I got around this by just adding to memstore in the log recovery process.
Not sure if there are other implications of this.

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