[GitHub] [incubator-superset] betodealmeida opened a new pull request #8172: Allow users to estimate query cost before executing them

[GitBox <gi...@apache.org>]

betodealmeida opened a new pull request #8172: Allow users to estimate query cost before executing them
URL: https://github.com/apache/incubator-superset/pull/8172
 
 
   ### CATEGORY
   
   Choose one
   
   - [ ] Bug Fix
   - [X] Enhancement (new features, refinement)
   - [ ] Refactor
   - [ ] Add tests
   - [ ] Build / Development Environment
   - [ ] Documentation
   
   ### SUMMARY
   <!--- Describe the change below, including rationale and design decisions -->
   
   We currently added to Presto support for estimating the number of bytes scanned (https://github.com/prestosql/presto/pull/806), and we'd like to surface that information to SQL Lab users before they actually run a query.
   
   This PR extends the DB specs with an `allows_cost_estimate` attribute and associated methods, allowing pre-execution costs to be computed from DBs that support it.
   
   In order to use it, the feature flag `ESTIMATE_QUERY_COST` must be enabled, and it needs to be explicitly turned on for each database that supports query cost estimation. When all those conditions are met, a new button will show up in SQL Lab, allowing users to run cost estimates for the whole query or for the selected SQL.
   
   ### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
   <!--- Skip this if not applicable -->
   
   DBs where the feature is not supported or not enabled are unmodified:
   
   <img width="1698" alt="Screen Shot 2019-09-04 at 8 48 46 AM" src="https://user-images.githubusercontent.com/1534870/64271606-72816180-cef2-11e9-93ea-d379c1fb2ed5.png">
   
   Here's a Presto DB:
   
   <img width="1698" alt="Screen Shot 2019-09-04 at 8 59 15 AM" src="https://user-images.githubusercontent.com/1534870/64271663-917ff380-cef2-11e9-931a-6b32bd843a2f.png">
   
   The result:
   
   <img width="1698" alt="Screen Shot 2019-09-04 at 8 58 57 AM" src="https://user-images.githubusercontent.com/1534870/64271692-a066a600-cef2-11e9-8e30-4f4a6bcb6752.png">
   
   And how errors (timeout, syntax errors) are surfaced:
   
   <img width="1698" alt="Screen Shot 2019-09-04 at 8 53 07 AM" src="https://user-images.githubusercontent.com/1534870/64271726-b2e0df80-cef2-11e9-8be8-35c5cce58f46.png">
   
   ### TEST PLAN
   <!--- What steps should be taken to verify the changes -->
   
   Tested with a Presto cluster that supports query cost estimation.
   
   ### ADDITIONAL INFORMATION
   <!--- Check any relevant boxes with "x" -->
   <!--- HINT: Include "Fixes #nnn" if you are fixing an existing issue -->
   - [ ] Has associated issue:
   - [X] Changes UI
   - [X] Requires DB Migration.
   - [X] Confirm DB Migration upgrade and downgrade tested.
   - [X] Introduces new feature or API
   - [ ] Removes existing feature or API
   
   ### REVIEWERS
   
   @etr2460 @mistercrunch 

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