[jira] [Commented] (IMPALA-9632) Implement ds_hll_sketch() and ds_hll_estimate() functions

["ASF subversion and git services (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IMPALA-9632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17126120#comment-17126120 ] 

ASF subversion and git services commented on IMPALA-9632:
---------------------------------------------------------

Commit 3713d5db8dcac540ce0b5cb45974054ca87792db in impala's branch refs/heads/master from Gabor Kaszab
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=3713d5d ]

IMPALA-9820: Pull Datasketches-5 HLL MurmurHash fix

There is a bug in DataSketches HLL MurmurHash where long strings are
over-read resulting a cardinality estimate that is more than 15% off
from the correct cardinality number. A recent upstream fix in Apache
DataSketches addresses this issue and this patch pulls it to Impala.

https://issues.apache.org/jira/browse/DATASKETCHES-5

Testing:
  - I used ds_hll_sketch() and ds_hll_estimate() functions from
    IMPALA-9632 to trigger DataSketches HLL functionality.
  - Ran DataSketches HLL on lineitem.l_comment in TPCH25_parquet to
    reproduce the issue. The symptom was that the actual result was
    around 15% off from the correct cardinality result (~69M vs 79M).
  - After applying this fix re-running the query gives much closer
    results, usually under 3% error range.

Change-Id: I84d73fce1e7a197c1f8fb49404b58ed9bb0b843d
Reviewed-on: http://gerrit.cloudera.org:8080/16026
Reviewed-by: Impala Public Jenkins <im...@cloudera.com>
Tested-by: Impala Public Jenkins <im...@cloudera.com>


> Implement ds_hll_sketch() and ds_hll_estimate() functions
> ---------------------------------------------------------
>
>                 Key: IMPALA-9632
>                 URL: https://issues.apache.org/jira/browse/IMPALA-9632
>             Project: IMPALA
>          Issue Type: New Feature
>          Components: Backend, Frontend
>            Reporter: Gabor Kaszab
>            Assignee: Gabor Kaszab
>            Priority: Major
>
> These should be built-in functions that use DataSketches functionality that was integrated by IMPALA-9631.
> ds_hll_sketch() should receive a primitive expression and return a sketch.
>  ds_hll_estimate() should receive a sketch and return a primitive that is the cardinality estimate for that set of data provided to the sketch.
> Usage:
>  select ds_hll_estimate(ds_hll_sketch(col_name)) from table_name;
>  Returns a cardinality estimate (similarly to ndv() ) for that particular column.
> Hive change that introduced the same: https://issues.apache.org/jira/browse/HIVE-22940



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