interweave_migrate/0 is a migration function that:

• Lists all pending migrations across multiple repositories.
• Sorts these migrations into a single list.
• Groups consecutive migrations by repository into "streaks".
• Executes the migrations in the correct order by processing each streak sequentially.

Why Use This Approach?

This function resolves dependencies between migrations that span across different repositories. The default migrate/0 function migrates each repository independently, which may result in migrations running in the wrong order when there are cross-repository dependencies.

Consider the following example (adapted from reality, not 100% accurate):

• Migration 1: The PostgreSQL (PG) repository creates a table named site_imports.
• Migration 2: The ClickHouse (CH) repository creates import_id columns in imported_* tables.
• Migration 3: The PG repository runs a data migration that utilizes both PG and CH databases, reading from the import_id column in imported_* tables.

The default migrate/0 would execute these migrations by repository, resulting in the following order:

1. Migration 1 (PG)
2. Migration 3 (PG)
3. Migration 2 (CH)

This sequence would fail at Migration 3, as the import_id columns in the CH repository have not been created yet.

interweave_migrate/0 addresses this issue by consolidating all pending migrations into a single, ordered queue:

1. Migration 1 (PG)
2. Migration 2 (CH)
3. Migration 3 (PG)

This ensures all dependencies are resolved in the correct order.