[jira] [Commented] (IGNITE-6089) SQL: Improve query parallelism architecture

["Andrew Mashenkov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IGNITE-6089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16147010#comment-16147010 ] 

Andrew Mashenkov commented on IGNITE-6089:
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Microsoft suggest next architecture of parallel query execution. 
Just leave it here, may it will help.

https://technet.microsoft.com/en-us/library/ms175097(v=sql.105).aspx

> SQL: Improve query parallelism architecture
> -------------------------------------------
>
>                 Key: IGNITE-6089
>                 URL: https://issues.apache.org/jira/browse/IGNITE-6089
>             Project: Ignite
>          Issue Type: Task
>          Components: sql
>    Affects Versions: 2.1
>            Reporter: Vladimir Ozerov
>              Labels: performance
>
> Currently query parallelism implement with static split of all indexes (including PK) for cache. This approach has several major disadvantages:
> 1) It improves scans, but slows down index and range lookups
> 2) Tables with different DOP cannot be used in the same query
> We need to fix that. Proposed plan:
> 1) No more index splits, ever - there is one and only one index always
> 2) Use preliminary execution plan, statistics (IGNITE-6079), CPU cores count and CPU load to estimate whether query will benefit from parallelism. 
> 3) if yes - split node-s single map query into several independent pieces. 
> Splitting can be achieved in one of the following ways:
> 1) Partition-based: e.g. if node owns partitions A, B, C and D, then we can split it to two queries - one over (A, B), another over (C, D). This could be useful for pure scans (e.g. DWH)
> 2) Histogram-based: e.g. if we have a query {{SELECT ... WHERE salary > 50}}, and we know salary distribution, we can split it into {{WHERE salary > 50 AND salary <= 200}} and {{WHERE salary > 200}}



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