We've discovered a problem that can cause the commit log to not get garbage
collected.  The problem occurs after tables are dropped.  There is a simple
fix, which is to add the following property to the hypertable.cfg file,
push the new file out to all slave machines in your Hypertable cluster, and
then restart your Hypertable instance.

Hypertable.RangeServer.CommitLog.FragmentRemoval.RangeReferenceRequired=false

The commit that introduced the problem was introduced to solve a data loss
problem that occurred under a very rare set of circumstances.  It occurred
with the following sequence:

1. RangeServer happened to not have any data in its in-memory CellCaches
2. A range was transferred to it
3. After the new range's transfer log was linked into the RangeServer's
commit log, but before the RSML entry was written for the new range, the
RangeServer crashed
4. The RangeServer was restarted

By setting the above property, you essentially re-introduce this problem,
however it is so rare (in particular #1) that it is not worth worrying
about.  I recommend that everyone running Hypertable add the above property
and restart.  We'll have a fix for it in the upcoming 0.9.6.3 release after
which you can remove the property.

- Doug

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