我有多个大型数据帧（大约30GB）称为as和bs，一个相对较小的数据帧（大约500MB〜1GB）称为spp。 我试图将spp缓存到内存中，以避免多次从数据库或文件中读取数据。
但是我发现如果我缓存了spp，物理计划表明即使spp被广播功能封装了，它也不会使用广播连接。 但是，如果我不保留该spp，则该计划将显示它使用广播连接。
有人熟悉吗？
scala> spp.cache
res38: spp.type = [id: bigint, idPartner: int ... 41 more fields]
scala> val as = acs.join(broadcast(spp), $"idsegment" === $"idAdnetProductSegment")
as: org.apache.spark.sql.DataFrame = [idsegmentpartner: bigint, ssegmentsource: string ... 44 more fields]
scala> as.explain
== Physical Plan ==
*SortMergeJoin [idsegment#286L], [idAdnetProductSegment#91L], Inner
:- *Sort [idsegment#286L ASC NULLS FIRST], false, 0
: +- Exchange hashpartitioning(idsegment#286L, 200)
: +- *Filter isnotnull(idsegment#286L)
: +- HiveTableScan [idsegmentpartner#282L, ssegmentsource#287, idsegment#286L], CatalogRelation `default`.`tblcustomsegmentcore`, org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [idcustomsegment#281L, idsegmentpartner#282L, ssegmentpartner#283, skey#284, svalue#285, idsegment#286L, ssegmentsource#287, datecreate#288]
+- *Sort [idAdnetProductSegment#91L ASC NULLS FIRST], false, 0
+- Exchange hashpartitioning(idAdnetProductSegment#91L, 200)
+- *Filter isnotnull(idAdnetProductSegment#91L)
+- InMemoryTableScan [id#87L, idPartner#88, idSegmentPartner#89, sSegmentSourceArray#90, idAdnetProductSegment#91L, idPartnerProduct#92L, idFeed#93, idGlobalProduct#94, sBrand#95, sSku#96, sOnlineID#97, sGTIN#98, sProductCategory#99, sAvailability#100, sCondition#101, sDescription#102, sImageLink#103, sLink#104, sTitle#105, sMPN#106, sPrice#107, sAgeGroup#108, sColor#109, dateExpiration#110, sGender#111, sItemGroupId#112, sGoogleProductCategory#113, sMaterial#114, sPattern#115, sProductType#116, sSalePrice#117, sSalePriceEffectiveDate#118, sShipping#119, sShippingWeight#120, sShippingSize#121, sUnmappedAttributeList#122, sStatus#123, createdBy#124, updatedBy#125, dateCreate#126, dateUpdated#127, sProductKeyName#128, sProductKeyValue#129], [isnotnull(idAdnetProductSegment#91L)]
+- InMemoryRelation [id#87L, idPartner#88, idSegmentPartner#89, sSegmentSourceArray#90, idAdnetProductSegment#91L, idPartnerProduct#92L, idFeed#93, idGlobalProduct#94, sBrand#95, sSku#96, sOnlineID#97, sGTIN#98, sProductCategory#99, sAvailability#100, sCondition#101, sDescription#102, sImageLink#103, sLink#104, sTitle#105, sMPN#106, sPrice#107, sAgeGroup#108, sColor#109, dateExpiration#110, sGender#111, sItemGroupId#112, sGoogleProductCategory#113, sMaterial#114, sPattern#115, sProductType#116, sSalePrice#117, sSalePriceEffectiveDate#118, sShipping#119, sShippingWeight#120, sShippingSize#121, sUnmappedAttributeList#122, sStatus#123, createdBy#124, updatedBy#125, dateCreate#126, dateUpdated#127, sProductKeyName#128, sProductKeyValue#129], true, 10000, StorageLevel(disk, memory, deserialized, 1 replicas)
+- *Scan JDBCRelation(tblSegmentPartnerProduct) [numPartitions=1] [id#87L,idPartner#88,idSegmentPartner#89,sSegmentSourceArray#90,idAdnetProductSegment#91L,idPartnerProduct#92L,idFeed#93,idGlobalProduct#94,sBrand#95,sSku#96,sOnlineID#97,sGTIN#98,sProductCategory#99,sAvailability#100,sCondition#101,sDescription#102,sImageLink#103,sLink#104,sTitle#105,sMPN#106,sPrice#107,sAgeGroup#108,sColor#109,dateExpiration#110,sGender#111,sItemGroupId#112,sGoogleProductCategory#113,sMaterial#114,sPattern#115,sProductType#116,sSalePrice#117,sSalePriceEffectiveDate#118,sShipping#119,sShippingWeight#120,sShippingSize#121,sUnmappedAttributeList#122,sStatus#123,createdBy#124,updatedBy#125,dateCreate#126,dateUpdated#127,sProductKeyName#128,sProductKeyValue#129] ReadSchema: struct<id:bigint,idPartner:int,idSegmentPartner:int,sSegmentSourceArray:string,idAdnetProductSegm...
scala> spp.unpersist
res40: spp.type = [id: bigint, idPartner: int ... 41 more fields]
scala> as.explain
== Physical Plan ==
*BroadcastHashJoin [idsegment#286L], [idAdnetProductSegment#91L], Inner, BuildRight
:- *Filter isnotnull(idsegment#286L)
: +- HiveTableScan [idsegmentpartner#282L, ssegmentsource#287, idsegment#286L], CatalogRelation `default`.`tblcustomsegmentcore`, org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [idcustomsegment#281L, idsegmentpartner#282L, ssegmentpartner#283, skey#284, svalue#285, idsegment#286L, ssegmentsource#287, datecreate#288]
+- BroadcastExchange HashedRelationBroadcastMode(List(input[4, bigint, true]))
+- *Scan JDBCRelation(tblSegmentPartnerProduct) [numPartitions=1] [id#87L,idPartner#88,idSegmentPartner#89,sSegmentSourceArray#90,idAdnetProductSegment#91L,idPartnerProduct#92L,idFeed#93,idGlobalProduct#94,sBrand#95,sSku#96,sOnlineID#97,sGTIN#98,sProductCategory#99,sAvailability#100,sCondition#101,sDescription#102,sImageLink#103,sLink#104,sTitle#105,sMPN#106,sPrice#107,sAgeGroup#108,sColor#109,dateExpiration#110,sGender#111,sItemGroupId#112,sGoogleProductCategory#113,sMaterial#114,sPattern#115,sProductType#116,sSalePrice#117,sSalePriceEffectiveDate#118,sShipping#119,sShippingWeight#120,sShippingSize#121,sUnmappedAttributeList#122,sStatus#123,createdBy#124,updatedBy#125,dateCreate#126,dateUpdated#127,sProductKeyName#128,sProductKeyValue#129] PushedFilters: [*IsNotNull(idAdnetProductSegment)], ReadSchema: struct<id:bigint,idPartner:int,idSegmentPartner:int,sSegmentSourceArray:string,idAdnetProductSegm...
答案 0 :(得分：3)
当分析计划尝试使用缓存数据时，会发生这种情况。它吞噬了用户（code）提供的ResolvedHint信息。
如果我们尝试执行df.explain(true)，则会发现在分析计划和优化计划之间丢失了提示，这是Spark尝试使用缓存数据的地方。
此问题已在最新版本的Spark中修复（多次尝试）。
最新的jira：https://issues.apache.org/jira/browse/SPARK-27674。
修补程序的代码（使用缓存表时考虑提示）：https://github.com/apache/spark/blame/master/sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala#L219