Thank you for the update. Tez fixes this kind of issue. ... View more

This is decided by the optimiser. Until Mappers are finished for that query,Reducers would not be stated. ... View more

I have checked the screenshot. This is not application concurrency. Reducer phases1 is waiting for all the mappers to get finished.  DAG is  decided by the optimizer. Are you using MAPREDUCE or Tez as an execution engine? ... View more

Can you try running 2 queries simultaneously and check?       ... View more

I am not sure,I believe you are hitting https://issues.apache.org/jira/browse/HIVE-21799   This fails at compile phase . ... View more

There are 2 things forground thread and background thread.   Foreground thread is used for parsing/complilation.The hive.server2.async.exec.threads determine how many concurrent threads can Hiveserver2 handle,it defaults to 500.   Background thread comes after compliation/parsing phase,where it runs Tez jobs. This depends on number of Tez AM .   In this case, you need to increase the Tez AM's. hive.server2.tez.sessions.per.default.queue=2 So if you have one Hiveserver2,it will run 2 background threads.    Please refer below document for more information:  https://community.cloudera.com/t5/Community-Articles/Hive-Understanding-concurrent-sessions-queue-allocation/ta-p/247407 ... View more

I see that you are using LLAP:   2020-06-30T09:46:08,840 INFO [16ba3bf1-1774-4bcd-b0a0-1d122df23311 HiveServer2-Handler-Pool: Thread-177864]: optimizer.ConvertJoinMapJoin (:()) - Memory monitor info set to : { isLlap: false executorsPerNode: 1 maxExecutorsOverSubscribeMemory: 3 memoryOverSubscriptionFactor: 0.20000000298023224 memoryCheckInterval: 100000 noConditionalTaskSize: 1717986918 adjustedNoConditionalTaskSize: 1717986918 hashTableInflationFactor: 2.0 threshold: 3435973836 } 2020-06-30T09:46:08,840 INFO [16ba3bf1-1774-4bcd-b0a0-1d122df23311 HiveServer2-Handler-Pool: Thread-177864]: optimizer.ConvertJoinMapJoin (:()) - maxJoinMemory: 1717986918  The Map join in LLAP works differently  then traditional Hiveserver2. You can go through https://community.cloudera.com/t5/Community-Articles/Map-Join-Memory-Sizing-For-LLAP/ta-p/247462 for more information . ... View more

Can you please provide the full trace ? What do you mean by first merge and 2nd merge? COuld you please brief us ? ... View more

I see that you use Active DIrecyory   Did you use the below property?   +++ <property> <name>hive.server2.authentication.ldap.Domain</name> <value>AD_Domain</value> </property> +++ ... View more