I've tested HBase 0.90 + HBase-trx 0.90.0 and i've run it over old data from 
0.89x using a variety of seeded unit test/QA data and cluster configurations.

But when it came time to upgrade some production data I got snagged on 
HBASE-3524. The gist of it is in Ryan's last points:

* compaction is "optional", meaning if it fails no data is lost, so you
should probably be fine.

* Older versions of the code did not write out time tracker data and
that is why your older files were giving you NPEs.

Makes sense.  But why did I not encounter this with my initial data upgrades on 
very similar data pkgs?

So I applied Ryan's patch, which simply assigns a default value 
(Long.MIN_VALUE) when a StoreFile lacks a timeRangeTracker and I "fixed" the 
data by forcing major compactions on the regions affected.  Preliminary poking 
has not shown any instability in the data since.

But I confess that I just don't have the time right now to really dig into the 
code and validate that there are no more gotchya's or data corruption that 
could have resulted.

I guess the questions that I have for the team are:

* What state would 9 out of 50 tables be in to miss the new 0.90.0 
timeRangeTracker injection before the first major compaction check?
* Where else is the new TimeRangeTracker used?  Could a StoreFile with a null 
timeRangeTracker have corrupted the data in other subtler ways?
* What other upgrade-related data changes might not have completed elsewhere?

Thanks,

James Kennedy
Project Manage
Troove Inc.

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