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https://issues.apache.org/jira/browse/IMPALA-10789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Tamas Mate updated IMPALA-10789:
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Target Version: Impala 4.2.0 (was: Impala 4.1.0)
> Early materialize expressions in ScanNode
> -----------------------------------------
>
> Key: IMPALA-10789
> URL: https://issues.apache.org/jira/browse/IMPALA-10789
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend, Frontend
> Affects Versions: Impala 4.1.0
> Reporter: Xianqing He
> Assignee: Xianqing He
> Priority: Major
>
> Impala uses the Late Materialize, to calculate expressions, for example,
> {code:java}
> SELECT SUM(col), COUNT(col), MIN(col), MAX(col)
> FROM (
> SELECT CAST(regexp_extract(string_col, '(\\d+)', 0) AS bigint) col
> FROM functional_parquet.alltypesagg
> ) t{code}
> The Plan likes
> {code:java}
> PLAN-ROOT SINK
> |
> 03:AGGREGATE [FINALIZE]
> | output: sum:merge(col), count:merge(col), min:merge(col), max:merge(col)
> | row-size=32B cardinality=1
> |
> 02:EXCHANGE [UNPARTITIONED]
> |
> 01:AGGREGATE
> | output: sum(CAST(regexp_extract(string_col, '(\\d+)', 0) AS BIGINT)),
> count(CAST(regexp_extract(string_col, '(\\d+)', 0) AS BIGINT)),
> min(CAST(regexp_extract(string_col, '(\\d+)', 0) AS BIGINT)),
> max(CAST(regexp_extract(string_col, '(\\d+)', 0) AS BIGINT))
> | row-size=32B cardinality=1
> |
> 00:SCAN HDFS [functional_parquet.alltypesagg]
> partitions=11/11 files=11 size=464.70KB
> row-size=15B cardinality=11.00K
> {code}
> In the aggregation phase, the expression in the parameters of the aggregation
> function is evaluated. In this way, the same expression that appears in
> multiple aggregation functions needs to be evaluated multiple times, which
> leads to long time consuming, especially for complex expressions, such as
> regular expressions.
> For analytic functions and contains union all,
>
> {code:java}
> SELECT SUM(int_col) OVER (PARTITION BY id )
> FROM (
> SELECT id
> , CASE
> WHEN id = 10 THEN tinyint_col
> WHEN string_col LIKE '%6%' THEN smallint_col
> END AS int_col
> FROM functional_parquet.alltypesagg
> UNION ALL
> SELECT id
> , CASE
> WHEN id = 10 THEN tinyint_col
> WHEN string_col LIKE '%6%' THEN smallint_col
> END AS int_col
> FROM functional_parquet.alltypes
> ) t
> {code}
> The plan likes
> {code:java}
> PLAN-ROOT SINK
> |
> 06:EXCHANGE [UNPARTITIONED]
> |
> 04:ANALYTIC
> | functions: sum(int_col)
> | partition by: id
> | row-size=14B cardinality=18.30K
> |
> 03:SORT
> | order by: id ASC NULLS FIRST
> | row-size=6B cardinality=18.30K
> |
> 05:EXCHANGE [HASH(id)]
> |
> 00:UNION
> | row-size=6B cardinality=18.30K
> |
> |--02:SCAN HDFS [functional_parquet.alltypes]
> | partitions=24/24 files=24 size=189.91KB
> | row-size=22B cardinality=7.30K
> |
> 01:SCAN HDFS [functional_parquet.alltypesagg]
> partitions=11/11 files=11 size=464.70KB
> row-size=24B cardinality=11.00K{code}
> In UnionNode， it will materialize expressions and prune columns.
> Currently UnionNode is single-threaded and ScanNode supports multi-threading,
> it will improve query performance if materialize expressions in ScanNode.
> We can specify which expressions require early materialize by hints, and
> Impala internally determines if the expression can be evaluated in ScanNode.
> {code:java}
> SELECT SUM(col), COUNT(col), MIN(col), MAX(col)
> FROM (
> SELECT CAST(regexp_extract(string_col, '(\\d+)', 0) AS bigint)
> col/*+materialize_expr*/
> FROM functional_parquet.alltypesagg
> ) t
> {code}
> This can materialize in ScanNode, but like the follow can't use early
> matrialize
> {code:java}
> SELECT SUM(col)
> FROM (
> SELECT CASE
> WHEN t1.id = 10 THEN t2.tinyint_col
> ELSE t2.smallint_col
> END AS col/*+materialize_expr*/
> FROM functional_parquet.alltypesagg t1
> JOIN functional_parquet.alltypes t2 ON t1.id = t2.id
> ) t
> {code}
>
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