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From Prasanth Jayachandran <>
Subject Re: Hive alter table concatenate loses data - can parquet help?
Date Tue, 08 Mar 2016 09:35:53 GMT
Hi Marcin

What hive version are you using? There has been some fixes to concatenate lately. I will let
you know if your hive version contains all fixes.


On Mar 8, 2016, at 3:29 AM, Mich Talebzadeh <<>>


can you please provide DDL for this table "show create table <TABLE>"

Dr Mich Talebzadeh


On 7 March 2016 at 23:25, Marcin Tustin <<>>
Hi All,

Following on from from our parquet vs orc discussion, today I observed hive's alter table
... concatenate command remove rows from an ORC formatted table.

1. Has anyone else observed this (fuller description below)? And
2. How to do parquet users handle the file fragmentation issue?

Description of the problem:

Today I ran a query to count rows by date. Relevant days below:
2016-02-28 16866
2016-03-06 219
2016-03-07 2863
I then ran concatenation on that table. Rerunning the same query resulted in:

2016-02-28 16866
2016-03-06 219
2016-03-07 1158

Note reduced count for 2016-03-07

I then ran concatenation a second time, and the query a third time:
2016-02-28 16344
2016-03-06 219
2016-03-07 1158

Now the count for 2016-02-28 is reduced.

This doesn't look like an elimination of duplicates occurring by design - these didn't all
happen on the first run of concatenation. It looks like concatenation just kind of loses data.

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