Data Model Changelog

Record changes to the ZooKeeper data model which require API version increases here.

When making a model change:

Increment the value of MODEL_API in model.py.
Update code to use the new API by default and add backwards-compatibility handling for older versions. This makes it easier to clean up backwards-compatibility handling in the future.
Make sure code that special cases model versions either references a model_api variable or has a comment like MODEL_API: > {version} so that we can grep for that and clean up compatability code that is no longer needed.
Add a test to test_model_upgrade.py.
Add an entry to this log so we can decide when to remove backwards-compatibility handlers.

Version 0

Prior Zuul version: 4.11.0
Description: This is an implied version as of Zuul 4.12.0 to initialize the series.

Prior Zuul version: 4.11.0
Description: No change since Version 0. This explicitly records the component versions in ZooKeeper.

Prior Zuul version: 5.0.0
Description: Changes the sempahore handle format from <item_uuid>-<job_name> to a dictionary with buildset path and job name.

Prior Zuul version: 5.0.0
Description: Add a new SupercedeEvent and use that for dequeuing of superceded items from other pipelines. This only affects the schedulers.