You are viewing a plain text version of this content. The canonical link for it is here.
Posted to issues@impala.apache.org by "Daniel Becker (Jira)" <ji...@apache.org> on 2020/07/21 09:11:00 UTC
[jira] [Resolved] (IMPALA-7655) Codegen output for conditional
functions (if,isnull, coalesce) is very suboptimal
[ https://issues.apache.org/jira/browse/IMPALA-7655?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Daniel Becker resolved IMPALA-7655.
-----------------------------------
Resolution: Fixed
> Codegen output for conditional functions (if,isnull, coalesce) is very suboptimal
> ---------------------------------------------------------------------------------
>
> Key: IMPALA-7655
> URL: https://issues.apache.org/jira/browse/IMPALA-7655
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Reporter: Tim Armstrong
> Assignee: Daniel Becker
> Priority: Major
> Labels: codegen, perf, performance
>
> https://gerrit.cloudera.org/#/c/11565/ provided a clue that an aggregation involving an if() function was very slow, 10x slower than the equivalent version using a case:
> {noformat}
> [localhost:21000] default> set num_nodes=1; set mt_dop=1; select count(case when l_orderkey is NULL then 1 else NULL end) from tpch10_parquet.lineitem;summary;
> NUM_NODES set to 1
> MT_DOP set to 1
> Query: select count(case when l_orderkey is NULL then 1 else NULL end) from tpch10_parquet.lineitem
> Query submitted at: 2018-10-04 11:17:31 (Coordinator: http://tarmstrong-box:25000)
> Query progress can be monitored at: http://tarmstrong-box:25000/query_plan?query_id=274b2a6f35cefe31:95a1964200000000
> +----------------------------------------------------------+
> | count(case when l_orderkey is null then 1 else null end) |
> +----------------------------------------------------------+
> | 0 |
> +----------------------------------------------------------+
> Fetched 1 row(s) in 0.51s
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> | Operator | #Hosts | Avg Time | Max Time | #Rows | Est. #Rows | Peak Mem | Est. Peak Mem | Detail |
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> | 01:AGGREGATE | 1 | 44.03ms | 44.03ms | 1 | 1 | 25.00 KB | 10.00 MB | FINALIZE |
> | 00:SCAN HDFS | 1 | 411.57ms | 411.57ms | 59.99M | -1 | 16.61 MB | 88.00 MB | tpch10_parquet.lineitem |
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> [localhost:21000] default> set num_nodes=1; set mt_dop=1; select count(if(l_orderkey is NULL, 1, NULL)) from tpch10_parquet.lineitem;summary;
> NUM_NODES set to 1
> MT_DOP set to 1
> Query: select count(if(l_orderkey is NULL, 1, NULL)) from tpch10_parquet.lineitem
> Query submitted at: 2018-10-04 11:23:07 (Coordinator: http://tarmstrong-box:25000)
> Query progress can be monitored at: http://tarmstrong-box:25000/query_plan?query_id=8e46ab1b84c4dbff:2786ca2600000000
> +----------------------------------------+
> | count(if(l_orderkey is null, 1, null)) |
> +----------------------------------------+
> | 0 |
> +----------------------------------------+
> Fetched 1 row(s) in 1.01s
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> | Operator | #Hosts | Avg Time | Max Time | #Rows | Est. #Rows | Peak Mem | Est. Peak Mem | Detail |
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> | 01:AGGREGATE | 1 | 422.07ms | 422.07ms | 1 | 1 | 25.00 KB | 10.00 MB | FINALIZE |
> | 00:SCAN HDFS | 1 | 511.13ms | 511.13ms | 59.99M | -1 | 16.61 MB | 88.00 MB | tpch10_parquet.lineitem |
> +--------------+--------+----------+----------+--------+------------+----------+---------------+-------------------------+
> {noformat}
> It turns out that this is because we don't have good codegen support for ConditionalFunction, and just fall back to emitting a call to the interpreted path: https://github.com/apache/impala/blob/master/be/src/exprs/conditional-functions.cc#L28
> See CaseExpr for an example of much better codegen support: https://github.com/apache/impala/blob/master/be/src/exprs/case-expr.cc#L178
--
This message was sent by Atlassian Jira
(v8.3.4#803005)