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From Gregory Chanan <gcha...@cloudera.com>
Subject Proposal: Remove explicit RowLocks in 0.96
Date Tue, 11 Dec 2012 21:52:31 GMT
Over in HBASE-7263 there has been some discussion about removing support
for explicit RowLocks in 0.96.  This would involve the following:
- Remove lockRow/unlockRow functions in HTable and similar
- Remove constructors for Put/Delete/Increment/Get that take RowLocks
- functions in HRegion no longer take lockIds (checkAndPut, append,
increment, etc).  This would affect coprocessors that call directly into
those functions.

I have a patch in HBASE-7315 with the details.

This would violate our usual rule of deprecating a feature one release
before removing.  The reasoning is as follows:
1) RowLocks are broken
 They are only kept in the memory associated with the region, so on a
split, region move, RS crash, they just disappear

2) 0.96 is special
Now seems like a good time to clean things up since we've made some
incompatible changes already (e.g. protobufing) and we could have a cleaner
client implementation

3) RowLocks have been deprecated "in spirit" for awhile
Here's a post from 2009 cautioning against their use:
http://bb10.com/java-hadoop-hbase-user/2009-09/msg00239.html
and a more recent example:
http://permalink.gmane.org/gmane.comp.java.hadoop.hbase.user/23488

4) RowLocks are hard to use effectively
Clients can deadlock or starve themselves, either by forgetting to release
the RowLocks or by starving other non-contending row operations by
occupying server handlers stuck waiting to acquire the locks.

Thoughts?

Greg

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