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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2022/06/06 02:19:46 UTC

[GitHub] [spark] beliefer commented on pull request #36295: [SPARK-38978][SQL] Support push down OFFSET to JDBC data source V2

beliefer commented on PR #36295:
URL: https://github.com/apache/spark/pull/36295#issuecomment-1146967033

   > Can we have some kind of performance numbers for "push down OFFSET could improves the performance."?
   
   For most JDBC data source, push down OFFSET could improves the performance.
   There are three reasons:
   1. JDBC data source knows the data distribution.
   2. JDBC data source constructs index for data.
   3. JDBC data source may have the query cache.
   4. Some JDBC data source running in native.
   5. push down OFFSET could reduce the I/O, then may reduce the shuffle size.


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