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From "Gopal V (JIRA)" <>
Subject [jira] [Created] (HIVE-5170) Sorted Bucketed Partitioned Insert hard-codes the reducer count == bucket count
Date Thu, 29 Aug 2013 20:36:52 GMT
Gopal V created HIVE-5170:

             Summary: Sorted Bucketed Partitioned Insert hard-codes the reducer count == bucket
                 Key: HIVE-5170
             Project: Hive
          Issue Type: Bug
          Components: Query Processor
    Affects Versions: 0.12.0
         Environment: Ubuntu LXC
            Reporter: Gopal V

When performing a hive sorted-partitioned insert, the insert optimizer hard-codes the number
of output files to the actual bucket count of the table.

We need at least that many reducers or if limited, switch to multi-spray (as implemented already),
but more reducers is wasteful as long as the HiveKey only contains the partition columns.

At this point, we're limited to reducers = n-bucket still, which is a problem for partitioning
requests which need to insert nearly a terabyte of data into a single-digit bucket count and
four-digit partition count.

Since that is routed by the hasCode of the HiveKey, we can ensure that works by modifying
the HiveKey to handle n-buckets internally.

Basically it should only generate hashCode = (sort_cols.hashCode() % n) routing only to n
reducers over-all, despite how many we spin up.

So far so good with the hard-coded reducer count.

But provided we fix the issues brought up by HIVE-5169, the insert becomes friendlier to a
higher reducer count as well.

At this juncture, we can modify the hashCode to be slightly more interesting.

hashCode = (part_cols.hashCode()*31 + (sort_cols.hashCode() % n)) 

This generates somewhere between n to partition_count * n unique hash-codes.

Since the sort-order & bucketing has to be maintained per-partition dir, distributing
this equally across any number of reducers will result in the scale-out of the reducer count.

This will allow a reducer count that will allow for far faster inserts of ORC data into a
partitioned/sorted table.

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