Enable fallback keys (multiple restore keys) in Pipeline Caching

Right now, a Pipeline Caching entry lookup can either be an exact hit or otherwise it is a miss. This can help with many scenarios, but is less effective for others.

Here’s my thinking on how we expand from that:

On saving a cache entry, it will continue to be stored at a specific key with an immutable value, however, one will be able to query it with multiple exact keys or key prefixes. Here’s an example:

variables:
  BUILD_KIT_CACHE: '$(Pipeline.Workspace)/buildkitcache'
steps:
  cache:
    path: $(System.DefaultWorkingDirectory)/buildkit
    key:
      - $(Build.SourceVersion)
        $(Build.SourceBranch)
        $(System.DefinitionId)
    fallbackKeys:
      - $(Build.SourceBranch)
        $(System.DefinitionId)
      - $(System.DefinitionId)

For saving, the cache entry will be stored at this “path”:

$(System.DefinitionId)/$(Build.SourceBranch)/$(Build.SourceVersion)

Lookups will occur in the following order until an entry is found. Should a particular lookup return multiple entries, the one that was most recently created will be selected.

First lookup:  $(System.DefinitionId)/$(Build.SourceBranch)/$(Build.SourceVersion)
Second lookup: $(System.DefinitionId)/$(Build.SourceBranch)/**
Third lookup:  $(System.DefinitionId)/**

[adrian-skybaker]

Yup, we will be updating the docs soon. 😃

That was nearly 10 months ago. Perhaps you could leave github issues open until the documentation is done? Otherwise it seems documentation never actually happens? And without it are they really completed features?

[fadnavistanmay]

Yup, we will be updating the docs soon. 😃