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From "Zoltan Haindrich (JIRA)" <>
Subject [jira] [Updated] (HIVE-18149) Stats: rownum estimation from datasize underestimates in most cases
Date Thu, 14 Dec 2017 13:59:00 GMT


Zoltan Haindrich updated HIVE-18149:
    Attachment: HIVE-18149.03wip01.patch

> Stats: rownum estimation from datasize underestimates in most cases
> -------------------------------------------------------------------
>                 Key: HIVE-18149
>                 URL:
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Statistics
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>         Attachments: HIVE-18149.01.patch, HIVE-18149.01wip01.patch, HIVE-18149.02.patch,
> rownum estimation is based on the following fact as of now:
> * datasize being used from the following sources:
> ** basicstats aggregates the loaded "on-heap" row sizes ; other readers are able to give
"raw size" estimation - I've checked orc; but I'm sure others will do the same....api docs
are a bit vague about the methods purpose...
> ** if the basicstats level info is not available; the filesystem level "file-size-sums"
are used as the "raw data size" ; which is multiplied by the [deserialization ratio|]
; which is currently 1.
> the problem with all of this is that deser factor is 1; and that rowsize counts in the
online object headers..
> example; 20 rows are loaded into a partition [columnstats_partlvl_dp.q|]
> after HIVE-18108 [this explain|]
will estimate the rowsize of the table to be 404 bytes; however the 20 rows of text is only
169 it ends up with 0 rows...

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