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https://issues.apache.org/jira/browse/SPARK-61192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-61192:
-----------------------------------
Labels: correctness pull-request-available (was: correctness)
> Non-deterministic or MATERIALIZED CTE whose body ends in COALESCE is
> evaluated once per reference
> -------------------------------------------------------------------------------------------------
>
> Key: SPARK-61192
> URL: https://issues.apache.org/jira/browse/SPARK-61192
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 4.0.1, 4.3.0, 5.0.0, 4.1.4
> Reporter: Artem Kupchinskiy
> Priority: Major
> Labels: correctness, pull-request-available
>
> A CTE that is not inlined (non-deterministic and referenced more than once,
> or {{AS MATERIALIZED}}) should be evaluated once:
> {{ReplaceCTERefWithRepartition}} puts a round-robin shuffle on top of the
> definition and all references reuse it. The shuffle is skipped when the
> definition already ends in any {{RepartitionOperation}}
> ({{canSkipExtraRepartition}}). A coalesce is {{Repartition(n, shuffle =
> false)}}, planned as {{CoalesceExec}}, so there is no exchange to reuse and
> every reference evaluates the body again.
> {code:python}
> import uuid
> from pyspark.sql.functions import udf
> spark.udf.register("random_uuid", udf(lambda:
> str(uuid.uuid4())).asNondeterministic())
> spark.sql("""
> WITH t AS (SELECT /*+ COALESCE(1) */ id, random_uuid() AS u FROM range(0,
> 1000, 1, 4))
> SELECT count(*) FROM t a JOIN t b ON a.u = b.u
> """).show()
> # expected 1000, returns 0 (AQE on and off; 4.0.1, 4.1.4, 4.3.0, master)
> {code}
> The same with {{WITH t AS MATERIALIZED (...)}} on master, and in plain SQL
> with {{reflect('java.util.UUID', 'randomUUID')}} instead of the UDF. The
> physical plan has two {{Coalesce 1}} subtrees, each with its own {{Range}},
> and no {{ReusedExchange}}.
> Proposed fix: for a coalesce root, put the round-robin shuffle below the
> coalesce and keep the coalesce on top, so the CTE still has at most n
> partitions. Cost: such CTEs now go through one round-robin shuffle.
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