[jira] [Resolved] (IMPALA-10287) Distribution strategy is sub-optimal for certain queries

["Aman Sinha (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-10287?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aman Sinha resolved IMPALA-10287.
---------------------------------
    Fix Version/s: Impala 4.0
       Resolution: Fixed

> Distribution strategy is sub-optimal for certain queries
> --------------------------------------------------------
>
>                 Key: IMPALA-10287
>                 URL: https://issues.apache.org/jira/browse/IMPALA-10287
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Frontend
>    Affects Versions: Impala 3.4.0
>            Reporter: Aman Sinha
>            Assignee: Aman Sinha
>            Priority: Major
>             Fix For: Impala 4.0
>
>
> I ran a simplified query (extracted from q78 of TPC-DS) on a 600GB dataset on an 8 node cluster. I forced the distribution strategy for the left outer join and compared Broadcast vs Hash Partition for different values of mt_dop.  The example query and results are shown below (elapsed times are in seconds):
> {noformat}
> Query (with shuffle or broadcast hint):
> select count(*)
>    from store_sales
>    left join [shuffle] store_returns on sr_ticket_number=ss_ticket_number 
>          and ss_item_sk=sr_item_sk
>    join date_dim on ss_sold_date_sk = d_date_sk
>    where sr_ticket_number is null
>    and d_year=2002;
> {noformat}
> ||mt_dop||Broadcast||Partition||
> |1|45|15|
> |2|37|9|
> |4|33|5|
> |8|31|4|
> |12|31|4|
> Given the nearly 7.5x speedup for partition distribution at mt_dop = 12 (which is the default), it indicates that the cost formula comparing the broadcast vs partition needs to be modified to take into account the mt_dop.



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