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https://issues.apache.org/jira/browse/IGNITE-24678?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantin Orlov reassigned IGNITE-24678:
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Assignee: Konstantin Orlov
> Sql. Introduce heuristic to exclude NLJ when HJ may be applied
> --------------------------------------------------------------
>
> Key: IGNITE-24678
> URL: https://issues.apache.org/jira/browse/IGNITE-24678
> Project: Ignite
> Issue Type: Improvement
> Components: sql
> Reporter: Konstantin Orlov
> Assignee: Konstantin Orlov
> Priority: Major
> Labels: ignite-3
>
> Currently, we have very primitive statistics which includes only table size.
> Moreover, they are gathered with some sort of throttling, preventing updating
> statistics for the same table more often than once per minute.
> The problem arises, when heavy query is executed immediately after all data
> has been uploaded to a table (which is actually every benchmark scenario):
> the first insert triggers gathering of table stats, resulting in table size
> close to 1 to be cached in statistic manager. During planning phase,
> cost-based optimizer makes wrong choices due to misleading statistics. The
> most expensive one is choosing NestedLoopJoin over HashJoin. For instance.
> the query 5 from TPC-H suite and scale factor 0.1, which normally completes
> under 1 second (373ms on my laptop), takes tens of minutes to complete with
> wrong join algorithm (it didn't finish in 15min, so I killed it).
> To mitigate the issue, we may introduce heuristic to avoid using NLJ for
> joins that can be executed with HJ.
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