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Posted to issues-all@impala.apache.org by "Balazs Jeszenszky (JIRA)" <ji...@apache.org> on 2018/09/05 09:38:00 UTC
[jira] [Created] (IMPALA-7528) Division by zero when computing
cardinalities of many to many joins on NULL columns
Balazs Jeszenszky created IMPALA-7528:
-----------------------------------------
Summary: Division by zero when computing cardinalities of many to many joins on NULL columns
Key: IMPALA-7528
URL: https://issues.apache.org/jira/browse/IMPALA-7528
Project: IMPALA
Issue Type: Improvement
Components: Frontend
Affects Versions: Impala 2.12.0
Reporter: Balazs Jeszenszky
The following:
{code:java}
| F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=1 |
| Per-Host Resources: mem-estimate=33.94MB mem-reservation=1.94MB |
| 02:HASH JOIN [INNER JOIN, BROADCAST] |
| | hash predicates: b.code = a.code |
| | fk/pk conjuncts: none |
| | runtime filters: RF000 <- a.code |
| | mem-estimate=1.94MB mem-reservation=1.94MB spill-buffer=64.00KB |
| | tuple-ids=1,0 row-size=163B cardinality=9223372036854775807 |
| | |
| |--03:EXCHANGE [BROADCAST] |
| | | mem-estimate=0B mem-reservation=0B |
| | | tuple-ids=0 row-size=82B cardinality=823 |
| | | |
| | F01:PLAN FRAGMENT [RANDOM] hosts=1 instances=1 |
| | Per-Host Resources: mem-estimate=32.00MB mem-reservation=0B |
| | 00:SCAN HDFS [default.sample_07 a, RANDOM] |
| | partitions=1/1 files=1 size=44.98KB |
| | stats-rows=823 extrapolated-rows=disabled |
| | table stats: rows=823 size=44.98KB |
| | column stats: all |
| | mem-estimate=32.00MB mem-reservation=0B |
| | tuple-ids=0 row-size=82B cardinality=823 |
| | |
| 01:SCAN HDFS [default.sample_08 b, RANDOM] |
| partitions=1/1 files=1 size=44.99KB |
| runtime filters: RF000 -> b.code |
| stats-rows=823 extrapolated-rows=disabled |
| table stats: rows=823 size=44.99KB |
| column stats: all |
| mem-estimate=32.00MB mem-reservation=0B |
| tuple-ids=1 row-size=82B cardinality=823 |
+--------------------------------------------------------------------+
{code}
is the result of both join columns having 0 as NDV.
https://github.com/cloudera/Impala/blob/cdh5-trunk/fe/src/main/java/org/apache/impala/planner/JoinNode.java#L368
should handle a potential division by zero.
IMPALA-7310 makes it a bit more likely that someone will run into this.
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