# Which Problems Are Solved
Milestones used existing events from a number of aggregates. OIDC
session is one of them. We noticed in load-tests that the reduction of
the oidc_session.added event into the milestone projection is a costly
business with payload based conditionals. A milestone is reached once,
but even then we remain subscribed to the OIDC events. This requires the
projections.current_states to be updated continuously.
# How the Problems Are Solved
The milestone creation is refactored to use dedicated events instead.
The command side decides when a milestone is reached and creates the
reached event once for each milestone when required.
# Additional Changes
In order to prevent reached milestones being created twice, a migration
script is provided. When the old `projections.milestones` table exist,
the state is read from there and `v2` milestone aggregate events are
created, with the original reached and pushed dates.
# Additional Context
- Closes https://github.com/zitadel/zitadel/issues/8800
Even though this is a feature it's released as fix so that we can back port to earlier revisions.
As reported by multiple users startup of ZITADEL after leaded to downtime and worst case rollbacks to the previously deployed version.
The problem starts rising when there are too many events to process after the start of ZITADEL. The root cause are changes on projections (database tables) which must be recomputed. This PR solves this problem by adding a new step to the setup phase which prefills the projections. The step can be enabled by adding the `--init-projections`-flag to `setup`, `start-from-init` and `start-from-setup`. Setting this flag results in potentially longer duration of the setup phase but reduces the risk of the problems mentioned in the paragraph above.
