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Yang, Tong 6182f91ba8 MRS component operation guide_normal 2.0.38.SP20 version 
Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com>
Co-authored-by: Yang, Tong <yangtong2@huawei.com>
Co-committed-by: Yang, Tong <yangtong2@huawei.com>
2022-12-09 14:55:21 +00:00

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Why Cannot Data Be Queried After the MapReduce Engine Is Switched After the Tez Engine Is Used to Execute Union-related Statements?

Question

Hive uses the Tez engine to execute union-related statements to write data. After Hive is switched to the MapReduce engine for query, no data is found.

Answer

When Hive uses the Tez engine to execute the union-related statement, the generated output file is stored in the HIVE_UNION_SUBDIR directory. After Hive is switched back to the MapReduce engine, files in the directory are not read by default. Therefore, data in the HIVE_UNION_SUBDIR directory is not read.

In this case, you can set mapreduce.input.fileinputformat.input.dir.recursive to true to enable union optimization and determine whether to read data in the directory.

Parent topic: Common Issues About Hive