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https://issues.apache.org/jira/browse/IMPALA-10964?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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carolinchen updated IMPALA-10964:
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Fix Version/s: (was: Impala 4.0.1)
> Add query option that limits skew query in runtime
> --------------------------------------------------
>
> Key: IMPALA-10964
> URL: https://issues.apache.org/jira/browse/IMPALA-10964
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 4.0.0
> Reporter: carolinchen
> Assignee: carolinchen
> Priority: Major
>
> Reject queries that skew value is too big when executing the query.
> Query skew refers to the situation in which some nodes are significantly
> behind other nodes in the process of concurrent execution of SQL.
> There are two style skews:
> 1. Row skew, which may be caused by unreasonable sql or uneven task
> distributions.
> 2. Time skew, which may be caused by different capability by execnode.
> Query skew will cause two effects:
> 1. For the skew node may execute slowly, which will slow down the query
> progress .
> 2. For the skew node may exhaust lots system resources( I/O, memory, rpc),
> which will
> affect other queries in the same host/ query pool.
> When the skew value reach unreasonale range, will affect the cluster status
> and other running queries. This is a mechanism to protect the cluster from
> potentially harmful queries(eg: mem_limit).
> In our environment, the SKEW_LIMIT query option is added to limit skewed
> query.
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