[SPARK-20927] Add cache operator to Unsupported Operations in Structured Streaming

• Type: Improvement
• Status: Resolved
• Priority: Trivial
• Resolution: Incomplete
• Affects Version/s: 2.2.0
• Component/s: Structured Streaming
• Labels: bulk-closed starter
• Assignee: Unassigned
• Reporter: Jacek Laskowski
• Created: 30/May/17 19:34
• Updated: 21/May/19 04:16
• Resolved: 21/May/19 04:16

Description

Just found out that cache is not allowed on streaming datasets.

cache on streaming datasets leads to the following exception:

scala> spark.readStream.text("files").cache
org.apache.spark.sql.AnalysisException: Queries with streaming sources must be executed with writeStream.start();;
FileSource[files]
  at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$.org$apache$spark$sql$catalyst$analysis$UnsupportedOperationChecker$$throwError(UnsupportedOperationChecker.scala:297)
  at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$$anonfun$checkForBatch$1.apply(UnsupportedOperationChecker.scala:36)
  at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$$anonfun$checkForBatch$1.apply(UnsupportedOperationChecker.scala:34)
  at org.apache.spark.sql.catalyst.trees.TreeNode.foreachUp(TreeNode.scala:127)
  at org.apache.spark.sql.catalyst.analysis.UnsupportedOperationChecker$.checkForBatch(UnsupportedOperationChecker.scala:34)
  at org.apache.spark.sql.execution.QueryExecution.assertSupported(QueryExecution.scala:63)
  at org.apache.spark.sql.execution.QueryExecution.withCachedData$lzycompute(QueryExecution.scala:74)
  at org.apache.spark.sql.execution.QueryExecution.withCachedData(QueryExecution.scala:72)
  at org.apache.spark.sql.execution.QueryExecution.optimizedPlan$lzycompute(QueryExecution.scala:78)
  at org.apache.spark.sql.execution.QueryExecution.optimizedPlan(QueryExecution.scala:78)
  at org.apache.spark.sql.execution.QueryExecution.sparkPlan$lzycompute(QueryExecution.scala:84)
  at org.apache.spark.sql.execution.QueryExecution.sparkPlan(QueryExecution.scala:80)
  at org.apache.spark.sql.execution.QueryExecution.executedPlan$lzycompute(QueryExecution.scala:89)
  at org.apache.spark.sql.execution.QueryExecution.executedPlan(QueryExecution.scala:89)
  at org.apache.spark.sql.execution.CacheManager$$anonfun$cacheQuery$1.apply(CacheManager.scala:104)
  at org.apache.spark.sql.execution.CacheManager.writeLock(CacheManager.scala:68)
  at org.apache.spark.sql.execution.CacheManager.cacheQuery(CacheManager.scala:92)
  at org.apache.spark.sql.Dataset.persist(Dataset.scala:2603)
  at org.apache.spark.sql.Dataset.cache(Dataset.scala:2613)
  ... 48 elided

It should be included in Structured Streaming's Unsupported Operations.

Issue Links

• supercedes: SPARK-20865 caching dataset throws "Queries with streaming sources must be executed with writeStream.start()"
• links to: [Github] Pull Request #18349 (ZiyueHuang)