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https://issues.apache.org/jira/browse/HIVE-11402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14646917#comment-14646917
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Carl Steinbach commented on HIVE-11402:
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bq. Note that running queries in parallel for single session is not
straightforward with jdbc, you need to spawn another thread as the
Statement.execute calls are blocking. I believe ODBC has non blocking query
execution API ...
I made a couple mistakes when I designed the HS2 API (the use of Thrift Enums
and Unions comes to mind), but by far the biggest mistake was allowing a 1:many
relationship between Sessions and Operations. At the time I thought there was a
chance that the ODBC spec required this, but now think this is something best
handled on the client side. Providing support for the 1:many Session:Operation
mapping results in a lot of additional complexity on the server-side, only to
yield a feature with a very high potential for misuse.
Rather than temporarily serializing operations against a given session, I
propose instead that we enforce a 1:1 mapping between HS2 sessions and active
operations. This is a backward incompatible change, but one which I think will
yield far better results in the long term.
> HS2 - disallow parallel query execution within a single Session
> ---------------------------------------------------------------
>
> Key: HIVE-11402
> URL: https://issues.apache.org/jira/browse/HIVE-11402
> Project: Hive
> Issue Type: Bug
> Components: HiveServer2
> Reporter: Thejas M Nair
>
> HiveServer2 currently allows concurrent queries to be run in a single
> session. However, every HS2 session has an associated SessionState object,
> and the use of SessionState in many places assumes that only one thread is
> using it, ie it is not thread safe.
> There are many places where SesssionState thread safety needs to be
> addressed, and until then we should serialize all query execution for a
> single HS2 session. -This problem can become more visible with HIVE-4239 now
> allowing parallel query compilation.-
> Note that running queries in parallel for single session is not
> straightforward with jdbc, you need to spawn another thread as the
> Statement.execute calls are blocking. I believe ODBC has non blocking query
> execution API, and Hue is another well known application that shares sessions
> for all queries that a user runs.
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