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Posted to issues@spark.apache.org by "Xiao Li (JIRA)" <ji...@apache.org> on 2017/01/06 06:31:01 UTC
[jira] [Commented] (SPARK-19093) Cached tables are not used in
SubqueryExpression
[ https://issues.apache.org/jira/browse/SPARK-19093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15803732#comment-15803732 ]
Xiao Li commented on SPARK-19093:
---------------------------------
{noformat}
/** Replaces segments of the given logical plan with cached versions where possible. */
def useCachedData(plan: LogicalPlan): LogicalPlan = {
plan transformDown {
case currentFragment =>
lookupCachedData(currentFragment)
.map(_.cachedRepresentation.withOutput(currentFragment.output))
.getOrElse(currentFragment)
}
}
{noformat}
The above function needs to consider the {{subqueryExpression}}.
> Cached tables are not used in SubqueryExpression
> ------------------------------------------------
>
> Key: SPARK-19093
> URL: https://issues.apache.org/jira/browse/SPARK-19093
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.2, 2.1.0
> Reporter: Josh Rosen
>
> See reproduction at https://databricks-prod-cloudfront.cloud.databricks.com/public/4027ec902e239c93eaaa8714f173bcfc/1903098128019500/2699761537338853/1395282846718893/latest.html
> Consider the following:
> {code}
> Seq(("a", "b"), ("c", "d"))
> .toDS
> .write
> .parquet("/tmp/rows")
> val df = spark.read.parquet("/tmp/rows")
> df.cache()
> df.count()
> df.createOrReplaceTempView("rows")
> spark.sql("""
> select * from rows cross join rows
> """).explain(true)
> spark.sql("""
> select * from rows where not exists (select * from rows)
> """).explain(true)
> {code}
> In both plans, I'd expect that both sides of the joins would read from the cached table for both the cross join and anti join, but the left anti join produces the following plan which only reads the left side from cache and reads the right side via a regular non-cahced scan:
> {code}
> == Parsed Logical Plan ==
> 'Project [*]
> +- 'Filter NOT exists#3994
> : +- 'Project [*]
> : +- 'UnresolvedRelation `rows`
> +- 'UnresolvedRelation `rows`
> == Analyzed Logical Plan ==
> _1: string, _2: string
> Project [_1#3775, _2#3776]
> +- Filter NOT predicate-subquery#3994 []
> : +- Project [_1#3775 AS _1#3775#4001, _2#3776 AS _2#3776#4002]
> : +- Project [_1#3775, _2#3776]
> : +- SubqueryAlias rows
> : +- Relation[_1#3775,_2#3776] parquet
> +- SubqueryAlias rows
> +- Relation[_1#3775,_2#3776] parquet
> == Optimized Logical Plan ==
> Join LeftAnti
> :- InMemoryRelation [_1#3775, _2#3776], true, 10000, StorageLevel(disk, memory, deserialized, 1 replicas)
> : +- *FileScan parquet [_1#3775,_2#3776] Batched: true, Format: Parquet, Location: InMemoryFileIndex[dbfs:/tmp/rows], PartitionFilters: [], PushedFilters: [], ReadSchema: struct<_1:string,_2:string>
> +- Project [_1#3775 AS _1#3775#4001, _2#3776 AS _2#3776#4002]
> +- Relation[_1#3775,_2#3776] parquet
> == Physical Plan ==
> BroadcastNestedLoopJoin BuildRight, LeftAnti
> :- InMemoryTableScan [_1#3775, _2#3776]
> : +- InMemoryRelation [_1#3775, _2#3776], true, 10000, StorageLevel(disk, memory, deserialized, 1 replicas)
> : +- *FileScan parquet [_1#3775,_2#3776] Batched: true, Format: Parquet, Location: InMemoryFileIndex[dbfs:/tmp/rows], PartitionFilters: [], PushedFilters: [], ReadSchema: struct<_1:string,_2:string>
> +- BroadcastExchange IdentityBroadcastMode
> +- *Project [_1#3775 AS _1#3775#4001, _2#3776 AS _2#3776#4002]
> +- *FileScan parquet [_1#3775,_2#3776] Batched: true, Format: Parquet, Location: InMemoryFileIndex[dbfs:/tmp/rows], PartitionFilters: [], PushedFilters: [], ReadSchema: struct<_1:string,_2:string>
> {code}
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