[
https://issues.apache.org/jira/browse/HIVE-17896?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Gopal V updated HIVE-17896:
---------------------------
Description:
For TPC-DS Query27, the TopN operation is delayed by the group-by - the
group-by operator buffers up all the rows before discarding the 99% of the rows
in the TopN Hash within the ReduceSink Operator.
The RS TopN operator is very restrictive as it only supports doing the
filtering on the shuffle keys, but it is better to do this before breaking the
vectors into rows and losing the isRepeating properties.
Adding a TopN operator in the physical operator tree allows the following to
happen.
GBY->RS(Top=1)
can become
TopN(1)->GBY->RS(Top=1)
So that, the TopN can remove rows before they are buffered into the GBY and
consume memory.
Here's the equivalent implementation in Presto
https://github.com/prestodb/presto/blob/master/presto-main/src/main/java/com/facebook/presto/operator/TopNOperator.java#L35
Adding this as a sub-feature of GroupBy prevents further optimizations if the
GBY is on keys "a,b,c" and the TopN is on just "a".
was:
For TPC-DS Query27, the TopN operation is delayed by the group-by - the
group-by operator buffers up all the rows before discarding the 99% of the rows
in the TopN Hash within the ReduceSink Operator.
The RS TopN operator is very restrictive as it only supports doing the
filtering on the shuffle keys, but it is better to do this before breaking the
vectors into rows and losing the isRepeating properties.
Adding a TopN operator in the physical operator tree allows the following to
happen.
GBY->RS(Top=1)
can become
TopN(1)->GBY->RS(Top=1)
So that, the TopN can remove rows before they are buffered into the GBY and
consume memory.
Here's the equivalent implementation in Presto
https://github.com/prestodb/presto/blob/master/presto-main/src/main/java/com/facebook/presto/operator/TopNOperator.java#L35
> TopN: Create a standalone vectorizable TopN operator
> ----------------------------------------------------
>
> Key: HIVE-17896
> URL: https://issues.apache.org/jira/browse/HIVE-17896
> Project: Hive
> Issue Type: New Feature
> Components: Operators
> Affects Versions: 3.0.0
> Reporter: Gopal V
>
> For TPC-DS Query27, the TopN operation is delayed by the group-by - the
> group-by operator buffers up all the rows before discarding the 99% of the
> rows in the TopN Hash within the ReduceSink Operator.
> The RS TopN operator is very restrictive as it only supports doing the
> filtering on the shuffle keys, but it is better to do this before breaking
> the vectors into rows and losing the isRepeating properties.
> Adding a TopN operator in the physical operator tree allows the following to
> happen.
> GBY->RS(Top=1)
> can become
> TopN(1)->GBY->RS(Top=1)
> So that, the TopN can remove rows before they are buffered into the GBY and
> consume memory.
> Here's the equivalent implementation in Presto
> https://github.com/prestodb/presto/blob/master/presto-main/src/main/java/com/facebook/presto/operator/TopNOperator.java#L35
> Adding this as a sub-feature of GroupBy prevents further optimizations if the
> GBY is on keys "a,b,c" and the TopN is on just "a".
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
