Simhadri G created HIVE-26009:
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Summary: Determine number of buckets for implicitly bucketed
ACIDv2 tables
Key: HIVE-26009
URL: https://issues.apache.org/jira/browse/HIVE-26009
Project: Hive
Issue Type: Improvement
Reporter: Simhadri G
Assignee: Simhadri G
Hive tries to set number of reducers equal to number of buckets here:
[https://github.com/apache/hive/blob/9857c4e584384f7b0a49c34bc2bdf876c2ea1503/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java#L6958]
The numberOfBuckets for implicitly bucketed tables is set to -1 by default.
When this is the case, it is left to hive to estimate the number of reducers
required the job, based on job input, and configuration parameters.
[https://github.com/apache/hive/blob/9857c4e584384f7b0a49c34bc2bdf876c2ea1503/ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java#L3369]
This estimate is not optimal in all cases. In the worst case, it case result in
a single reducer being launched , which can lead to a significant bottleneck in
performance .
Ideally, the number of reducers launched should equal to number of buckets,
which is the case for explicitly bucketed tables.
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