commit | f4273a40fe2e2ab0806f0324ecf33a25b3df6279 | [log] [tgz] |
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author | Shant Hovsepian <shant@cloudera.com> | Thu Aug 20 23:16:27 2020 -0400 |
committer | Impala Public Jenkins <impala-public-jenkins@cloudera.com> | Tue Sep 01 08:54:42 2020 +0000 |
tree | ccf500d38cfc128158c0aac0ad5a0fb320f73cc5 | |
parent | f85dbff97618066d60f37736808c8c24aa0a98e5 [diff] |
IMPALA-7310: Partial fix for NDV cardinality with NULLs. This fix just handles the case where a column's cardinality is zero however it's nullable and we have null stats to indicate there are null values, therefore we adjust the cardinality from 0 to 1. The cardinality of zero was especially problematic when calculating cardinalities for multiple predicates with multiplication. The 0 would propagate up the plan tree and result in poor plan choices such as always using broadcast joins where shuffle would've been more optimal. Testing: * 26 Node TPC-DS 30TB run had better plans for Q4 and Q11 - Q4 172s -> 80s - Q11 103s -> 77s * CardinalityTest * TpcdsPlannerTest Change-Id: Iec967053b4991f8c67cde62adf003cbd3f429032 Reviewed-on: http://gerrit.cloudera.org:8080/16349 Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Lightning-fast, distributed SQL queries for petabytes of data stored in Apache Hadoop clusters.
Impala is a modern, massively-distributed, massively-parallel, C++ query engine that lets you analyze, transform and combine data from a variety of data sources:
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