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9. Database migration squashing

· One min read
Mithril Team

Status​

Accepted

Context​

Over time, many database migrations have accumulated in Mithril nodes. Since these migrations are applied sequentially, the resulting database schema has become difficult to understand and maintain.

Decision​

To address this, the team decided to implement migration squashing once too many migrations have accumulated for a store. This process consolidates all existing migrations into a single, equivalent migration.

Consequences​

  • This applies to the migrations of all Mithril node stores
  • A squashed migration will be applied when a database is initialized for the first time
  • A squashed migration must be optional and should only run if it has not been previously applied with the equivalent migration sequence
  • Some nodes may have only partially applied the equivalent sequence of migrations and cannot apply the squashed migration immediately:
    • They must first run the migration using the latest distribution that does not include the squashed migration, ensuring their database is prepared to apply it
    • This distribution is associated with a squashed migration to provide a smooth user experience.