[MDEV-10059] Compute window functions with same sorting criteria simultaneously Created: 2016-05-12  Updated: 2016-09-14  Resolved: 2016-09-13

Status: Closed
Project: MariaDB Server
Component/s: Optimizer - Window functions
Fix Version/s: 10.2.2

Type: Task Priority: Major
Reporter: Vicențiu Ciorbaru Assignee: Vicențiu Ciorbaru
Resolution: Fixed Votes: 0
Labels: None

Sprint: 10.2.1-3, 10.2.1-4, 10.2.1-5, 10.2.2-1, 10.2.2-1, 10.2.2-2, 10.2.2-1, 10.2.2-2, 10.2.2-3

 Description   

While computing window functions, we can take advantage of the general use case where they specify the same PARTITION and ORDER BY criteria.
We already take advantage of this fact by only sorting the internal tmp table as few times as possible. Filling the window function values within the internal tmp table can be performed during one pass / sort as well. Currently we do a pass for each window function.

In order to do this, we must refactor the computation code to be aware of multiple functions during a scan.

 Comments   
Comment by Vicențiu Ciorbaru [ 2016-09-06 ]

While refactoring code for this issue, I have reduced the algorithms that we have for computing window functions to only one. Stream-able functions such as RANK and ROW_NUMBER are now computed by making use of cursors, instead of a specific construct just for them. Performance wise they behave the same as before.

Comment by Vicențiu Ciorbaru [ 2016-09-13 ]

Implemented with:

https://github.com/MariaDB/server/commit/23e8b508a00a23653da436519371943487ad6fe4

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