[GitHub] [airflow] ashb opened a new pull request #6792: [AIRFLOW-5930] Use cached-SQL query building for hot-path queries

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ashb opened a new pull request #6792: [AIRFLOW-5930] Use cached-SQL query building for hot-path queries
URL: https://github.com/apache/airflow/pull/6792
 
 
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   ### Jira
   
   - [x] https://issues.apache.org/jira/browse/AIRFLOW-5930
   
   ### Description
   
   - [ ] Building the SQL string for this query takes up about 25% of the time that the DAG parsing process spends, so replacing this one query should help speed up the rate at which the scheduler can queue tasks.
   
     See https://docs.sqlalchemy.org/en/13/orm/extensions/baked.html for more info. The docs explain a lot of how/why this works, so rather than rebuilding them from string 10s of times (once per task per active dag run) we cache the build SQL string!
   
     I will collect up-to-date performance numbers against master, but this makes the "dag parsing" process of the scheduler (which creates and updates dag runs, and creates Task Instances) about 2x quicker:
   
     Concurrent DagRuns | Tasks | Before | After | Speedup
     -- | -- | -- | -- | --
     2 | 12 | 0.146s (±0.0163s) | 0.074s (±0.0037s) | x1.97
     10 | 12 | 1.11s (±0.0171s) | 0.266s (±0.0229s) | x4.17
     40 | 12 | 4.28s (±0.101s) | 0.852s (±0.0113s) | x5.02
     40 | 40 | 6.72s (±0.067s) | 2.659s (±0.0283s) | x2.53
   
   
   
   ### Tests
   
   - [x] No new tests, no change in behaviour.
   
   ### Commits
   
   - [ ] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [ ] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   

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