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From Raymond Lau <raymond.lau...@gmail.com>
Subject Instagram's "Anticolumn"
Date Sun, 07 Sep 2014 08:25:01 GMT
So I watched Instagram’s presentation about Cassandra and how they handle undos/deletes (http://youtu.be/xDtclzE4ydA?t=12m55s)
and how to get around the race condition that a get-before-write causes.  

They use this anti-column that stores an action where the first component of the composite
column is a 0 or 1, 0 if it’s an undo, 1 if it’s the action.  The second component of
the composite column is the md5 hash of the activity if it is an undo (anti-column = 0), and
the actual data pertaining to the activity if anti-column = 1.  Why is the undo activity
stored as an md5 hash?  Do they md5 hash everything (both anti column = 1 and anti column
= 0), compare the two lists, and negate everything where the md5 hashes match?  

-Raymond
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