Jacek Laskowski created SPARK-20927:
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Summary: Add cache operator to Unsupported Operations in
Structured Streaming
Key: SPARK-20927
URL: https://issues.apache.org/jira/browse/SPARK-20927
Project: Spark
Issue Type: Improvement
Components: Structured Streaming
Affects Versions: 2.3.0
Reporter: Jacek Laskowski
Priority: Trivial
Just [found
out|https://stackoverflow.com/questions/42062092/why-does-using-cache-on-streaming-datasets-fail-with-analysisexception-queries]
that {{cache}} is not allowed on streaming datasets.
{{cache}} on streaming datasets leads to the following exception:
{code}
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
{code}
It should be included in Structured Streaming's [Unsupported
Operations|http://spark.apache.org/docs/latest/structured-streaming-programming-guide.html#unsupported-operations].
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