Github user marmbrus commented on the pull request:

    https://github.com/apache/spark/pull/6351#issuecomment-105712920
  
    That is not fundamentally a problem.  Honestly some more thought probably 
needs to be put into the batches.  Really the only reasons for splitting are 
the following:
     - Large batches are inherently more costly as you must go through every 
rule, even if only a small number are making changes.  So if rules will never 
interact they can be in separate batches.
     - However, large batches are more powerful as there is more opportunity 
for rules to interact
     - Its possible for rules to undo the result of other rules.  In this case 
they *must* be in separate batches or it will go back and forth till the limit 
is reached
     - Another reason for batches is satisfying preconditions. (i.e. a plan 
must be analyzed before optimizing it).


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