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Posted to dev@hive.apache.org by "Illya Yalovyy (JIRA)" <ji...@apache.org> on 2015/09/18 19:26:04 UTC
[jira] [Created] (HIVE-11882) Fetch optimizer should stop source
files traversal once it exceeds the hive.fetch.task.conversion.threshold
Illya Yalovyy created HIVE-11882:
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Summary: Fetch optimizer should stop source files traversal once it exceeds the hive.fetch.task.conversion.threshold
Key: HIVE-11882
URL: https://issues.apache.org/jira/browse/HIVE-11882
Project: Hive
Issue Type: Improvement
Components: Physical Optimizer
Affects Versions: 1.0.0
Reporter: Illya Yalovyy
Hive 1.0's fetch optimizer tries to optimize queries of the form "select <C> from <T> where <F> limit <L>" to a fetch task (see the hive.fetch.task.conversion property). This optimization gets the lengths of all the files in the specified partition and does some comparison against a threshold value to determine whether it should use a fetch task or not (see the hive.fetch.task.conversion.threshold property). This process of getting the length of all files. One of the main problems in this optimization is the fetch optimizer doesn't seem to stop once it exceeds the hive.fetch.task.conversion.threshold. It works fine on HDFS, but could cause a significant performance degradation on other supported file systems.
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