[HIVE-17532] Hive on Spark query compilation starts Spark session

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 2.2.0
• Component/s: HiveServer2
• Assignee: Unassigned Assign to me
• Reporter: Peter Csaszar
• Created: 14/Sep/17 12:50
• Updated: 14/Sep/17 13:05

Description

Hive on Spark query compilation starts a new Spark session when some kind of aggregation is present:

0: jdbc:hive2://localhost:10000/default> set hive.execution.engine=spark;
No rows affected (0.013 seconds)
0: jdbc:hive2://localhost:10000/default> explain select distinct label0 from iris;
INFO : Compiling command(queryId=hive_20170912151212_914ee322-28dd-442a-9dd9-7ed00a6a8caf): explain select distinct label0 from iris
INFO : Semantic Analysis Completed
INFO : Returning Hive schema: Schema(fieldSchemas:[FieldSchema(name:Explain, type:string, comment:null)], properties:null)
INFO : Completed compiling command(queryId=hive_20170912151212_914ee322-28dd-442a-9dd9-7ed00a6a8caf); Time taken: 40.594 seconds

Spark job started, all consecutive explain statements are fast:

0: jdbc:hive2://localhost:10000/default> explain select distinct a1 from iris;
INFO : Compiling command(queryId=hive_20170912151414_faacda24-290e-48bb-9daf-3f301fc170c1): explain select distinct label0 from iris
INFO : Semantic Analysis Completed
INFO : Returning Hive schema: Schema(fieldSchemas:[FieldSchema(name:Explain, type:string, comment:null)], properties:null)
INFO : Completed compiling command(queryId=hive_20170912151414_faacda24-290e-48bb-9daf-3f301fc170c1); Time taken: 0.275 seconds

Killing the Spark job, the same query is still fast, and no new Spark job has been started:

0: jdbc:hive2://localhost:10000/default> explain select distinct a2 from iris;
INFO : Compiling command(queryId=hive_20170912151616_a7ea83b6-03ce-4636-b3d4-be6feadcde35): explain select distinct label0 from iris
INFO : Semantic Analysis Completed
INFO : Returning Hive schema: Schema(fieldSchemas:[FieldSchema(name:Explain, type:string, comment:null)], properties:null)
INFO : Completed compiling command(queryId=hive_20170912151616_a7ea83b6-03ce-4636-b3d4-be6feadcde35); Time taken: 0.213 seconds

The code in question:
SetSparkReducerParallelism.java:
sparkSessionManager = SparkSessionManagerImpl.getInstance();
sparkSession = SparkUtilities.getSparkSession(context.getConf(), sparkSessionManager);
sparkMemoryAndCores = sparkSession.getMemoryAndCores();

The created Spark session is used for getting the number of cores and memory only. This could be determined from the configurations, without actually starting a session.