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

["Vladimir Ozerov (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IGNITE-6089?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Ozerov updated IGNITE-6089:
------------------------------------
    Labels: performance sql-engine  (was: performance)

> 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
>            Priority: Major
>              Labels: performance, sql-engine
>
> 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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