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From Gopal Vijayaraghavan <>
Subject Re: merge small orc files
Date Tue, 21 Apr 2015 02:41:35 GMT

>How to set the configuration hive-site.xml to automatically merge small
>orc file (output from mapreduce job) in hive 0.14 ?

Hive cannot add work-stages to a map-reduce job.

Hive follows merge.mapfiles=true when Hive generates a plan, by adding
more work to the plan as a conditional task.

>-rwxr-xr-x   1 root hdfs      29072 2015-04-20 15:23

This looks like it was written by an MRv2 Reducer and not by the Hive
FileSinkOperator & handled by the MR outputcommitter instead of the Hive

But 0.14 has an option which helps ³hive.merge.orcfile.stripe.level². If
that is true (like your setting), then do

³alter table <table> concatenate²

which effectively concatenates ORC blocks (without decompressing them),
while maintaining metadata linkage of start/end offsets in the footer.


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