[
https://issues.apache.org/jira/browse/IMPALA-9911?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Aman Sinha resolved IMPALA-9911.
--------------------------------
Fix Version/s: Impala 4.0
Resolution: Fixed
> IS [NOT] NULL predicate selectivity estimate is wrong if #nulls is 0
> --------------------------------------------------------------------
>
> Key: IMPALA-9911
> URL: https://issues.apache.org/jira/browse/IMPALA-9911
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 3.4.0
> Reporter: Aman Sinha
> Assignee: Aman Sinha
> Priority: Major
> Fix For: Impala 4.0
>
>
> Consider the tpcds customer table .. its c_current_addr_sk column has #Nulls
> = 0 as shown below.
> {noformat}
> tpcds> show column stats customer;
> +------------------------+--------+------------------+--------+----------+-------------------+
> | Column | Type | #Distinct Values | #Nulls | Max Size |
> Avg Size |
> +------------------------+--------+------------------+--------+----------+-------------------+
> ....
> | c_current_cdemo_sk | INT | 91558 | 3438 | 4 | 4
> |
> | c_current_hdemo_sk | INT | 7376 | 3431 | 4 | 4
> |
> | c_current_addr_sk | INT | 42003 | 0 | 4 | 4
> |
> ....
> {noformat}
> The cardinality estimate for the following predicates shows a default
> selectivity of 10% being applied which is not correct:
> {noformat}
> explain select c_current_addr_sk from customer where c_current_addr_sk is not
> null;
> | 00:SCAN HDFS [tpcds.customer] |
> | HDFS partitions=1/1 files=1 size=12.60MB |
> | predicates: c_current_addr_sk IS NOT NULL |
> | row-size=4B cardinality=10.00K |
> +------------------------------------------------------------+
> explain select c_current_addr_sk from customer where c_current_addr_sk is
> null;
> | 00:SCAN HDFS [tpcds.customer] |
> | HDFS partitions=1/1 files=1 size=12.60MB |
> | predicates: c_current_addr_sk IS NULL |
> | row-size=4B cardinality=10.00K |
> {noformat}
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
