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Hi..whats the difference between "Start Tez session at Initialization" and hive.execution.engine=tez properties?

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Expert Contributor

If both are not same how they are different? Can you please let me know?

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@Srikaran Jangidi

Start Tez session at Initialization - Enables a user to use HiveServer2 without enabling Tez for HiveServer2. Users might potentially want to run queries with Tez without a pool of sessions.

Default value is False

hive.execution.engine=tez - This setting determines whether Hive queries will be executed using Tez or MapReduce.

Default value is - If this value is set to "mr," Hive queries will be executed using MapReduce. If this value is set to "tez," Hive queries will be executed using Tez. All queries executed through HiveServer2 will use the specified hive.execution.engine setting.

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Expert Contributor

Let me put the question this way. If I have hive.execution.engine=tez; why do I need the property hive.server2.tez.initialize.default.sessions to set it to "True"? Whats the use-case for this property? I ran multiple tests but my hive.execution.engine property drives how the query works and not this default sessions property.

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Expert Contributor

@Benjamin Leonhardi

Thanks, This makes sense, so its always better to set the value to "True" rt?

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Master Guru

Personally I like it off. It binds extra resources in the cluster and the second query will be fast anyway. You also need to know how many sessions you want in advance since it will redistrube queries to the precreated seasons. If you don't care about the first query on a cold system being slow keeping it off is the safer choice IMO