[opt](coord) use single instance only with small limit #33888
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TPC-H: Total hot run time: 38386 ms |
TPC-DS: Total hot run time: 184048 ms |
ClickBench: Total hot run time: 29.97 s |
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TPC-H: Total hot run time: 38498 ms |
TPC-DS: Total hot run time: 184285 ms |
ClickBench: Total hot run time: 30.07 s |
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… limit involved (#39927) For queries like `select * from tbl limit 100;`, we should limit the parallelism to 1. We already have strategies in our code, but we can not control its behavior. So add session variables to control them. Previous pr like #33888 #36535 already has done something similar, this pr integrates them.
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… limit involved (apache#39927) For queries like `select * from tbl limit 100;`, we should limit the parallelism to 1. We already have strategies in our code, but we can not control its behavior. So add session variables to control them. Previous pr like apache#33888 apache#36535 already has done something similar, this pr integrates them.
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Proposed changes
Followup #31342
When executing simple query like
select * from tbl limit 1.Doris will use only one instance for each scan node, to reduce the fan-out of simple queries.
But if the limit number is large, eg, 1 billion, this logic is not suitable.
So I add a new session variable
limit_rows_for_single_instance, default is 10000.Only if the limit number is lower than this value, Doris will use one instance for scan node.
Further comments
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