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https://issues.apache.org/jira/browse/SPARK-25196?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-25196:
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Assignee: (was: Apache Spark)
> Analyze column statistics in cached query
> -----------------------------------------
>
> Key: SPARK-25196
> URL: https://issues.apache.org/jira/browse/SPARK-25196
> Project: Spark
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 2.3.1
> Reporter: Takeshi Yamamuro
> Priority: Minor
>
> In common usecases, users read catalog table data, join/aggregate them, and
> then cache the result for following reuse. Since we are only allowed to
> analyze column statistics in catalog tables via ANALYZE commands, the
> optimization depends on non-existing or inaccurate column statistics of
> cached data. So, I think it'd be nice if Spark could analyze cached data and
> hold temporary column statistics for InMemoryRelation.
> For example, we might be able to add a new API (e.g.,
> analyzeColumnCacheQuery) to do so in CacheManager;
> POC:
> [https://github.com/apache/spark/compare/master...maropu:AnalyzeCacheQuery]
> {code:java}
> scala> sql("SET spark.sql.cbo.enabled=true")
> scala> sql("SET spark.sql.statistics.histogram.enabled=true")
> scala> spark.range(1000).selectExpr("id % 33 AS c0", "rand() AS c1", "0 AS
> c2").write.saveAsTable("t")
> scala> sql("ANALYZE TABLE t COMPUTE STATISTICS FOR COLUMNS c0, c1, c2")
> scala> val cacheManager = spark.sharedState.cacheManager
> scala> def printColumnStats(data: org.apache.spark.sql.DataFrame) = {
> | data.queryExecution.optimizedPlan.stats.attributeStats.foreach {
> | case (k, v) => println(s"[$k]: $v")
> | }
> | }
> scala> def df() = spark.table("t").groupBy("c0").agg(count("c1").as("v1"),
> sum("c2").as("v2"))
> // Prints column statistics in catalog table `t`
> scala> printColumnStats(spark.table("t"))
> [c0#7073L]:
> ColumnStat(Some(33),Some(0),Some(32),Some(0),Some(8),Some(8),Some(Histogram(3.937007874015748,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@209c0be5)))
> [c1#7074]:
> ColumnStat(Some(997),Some(5.958619423369615E-4),Some(0.9988009488973438),Some(0),Some(8),Some(8),Some(Histogram(3.937007874015748,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@4ef69c53)))
> [c2#7075]:
> ColumnStat(Some(1),Some(0),Some(0),Some(0),Some(4),Some(4),Some(Histogram(3.937007874015748,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@7cbaf548)))
> // Prints column statistics on query result `df`
> scala> printColumnStats(df())
> [c0#7073L]:
> ColumnStat(Some(33),Some(0),Some(32),Some(0),Some(8),Some(8),Some(Histogram(3.937007874015748,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@209c0be5)))
> // Prints column statistics on cached data of `df`
> scala> printColumnStats(df().cache)
> <No Column Statistics>
> // A new API described above
> scala> cacheManager.analyzeColumnCacheQuery(df(), "v1" :: "v2" :: Nil)
>
>
> // Then, prints again
> scala> printColumnStats(df())
> [v1#7101L]:
> ColumnStat(Some(2),Some(30),Some(31),Some(0),Some(8),Some(8),Some(Histogram(0.12992125984251968,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@e2ff893)))
> [v2#7103L]:
> ColumnStat(Some(1),Some(0),Some(0),Some(0),Some(8),Some(8),Some(Histogram(0.12992125984251968,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@1498a4d)))
> scala> cacheManager.analyzeColumnCacheQuery(df(), "c0" :: Nil)
> scala> printColumnStats(df())
> [v1#7101L]:
> ColumnStat(Some(2),Some(30),Some(31),Some(0),Some(8),Some(8),Some(Histogram(0.12992125984251968,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@e2ff893)))
> [v2#7103L]:
> ColumnStat(Some(1),Some(0),Some(0),Some(0),Some(8),Some(8),Some(Histogram(0.12992125984251968,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@1498a4d)))
> [c0#7073L]:
> ColumnStat(Some(33),Some(0),Some(32),Some(0),Some(8),Some(8),Some(Histogram(0.12992125984251968,[Lorg.apache.spark.sql.catalyst.plans.logical.HistogramBin;@626bcfc8)))
> {code}
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