[jira] [Updated] (IMPALA-7653) Improve accuracy of compute incremental stats cardinality estimation

["Balazs Jeszenszky (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-7653?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Balazs Jeszenszky updated IMPALA-7653:
--------------------------------------
    Summary: Improve accuracy of compute incremental stats cardinality estimation  (was: Improve accuracy of incremental stats cardinality estimation)

> Improve accuracy of compute incremental stats cardinality estimation
> --------------------------------------------------------------------
>
>                 Key: IMPALA-7653
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7653
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Frontend
>    Affects Versions: Impala 3.0
>            Reporter: Balazs Jeszenszky
>            Priority: Major
>
> Currently, the operators of a compute [incremental] stats' subquery rely on combined selectivities - as usual - to estimate cardinality, e.g. during aggregation. For example, note the expected cardinality of the aggregation on this subquery:
> {code}
> F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=4
> Per-Host Resources: mem-estimate=305.20GB mem-reservation=136.00MB
> 01:AGGREGATE [STREAMING]
> |  output: [...]
> |  group by: col_a, col_b, col_c
> |  mem-estimate=76.21GB mem-reservation=34.00MB spill-buffer=2.00MB
> |  tuple-ids=1 row-size=104.83KB cardinality=693000
> |
> 00:SCAN HDFS [default.test, RANDOM]
>    partitions=1/554 files=1 size=109.65MB
>    stats-rows=1506374 extrapolated-rows=disabled
>    table stats: rows=821958291 size=unavailable
>    column stats: all
>    mem-estimate=88.00MB mem-reservation=0B
>    tuple-ids=0 row-size=2.06KB cardinality=1506374
> {code}
> This was generated as a result of compute incremental stats on a single partition, so the output of that aggregation is a single row. Due to the width of the intermediate rows, such overestimations lead to bloated memory estimates. Since the amount of partitions to be updated is known at plan-time, Impala could use that to set the aggregation's cardinality.



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