Memory leak: migratePromise() doesn't clean up internal replication state

[OskarD]

Summary

Calling collection.migratePromise() causes a memory leak because the internal replication state is never properly cleaned up after migration completes.

Root Cause

In rx-migration-state.ts, the migrateStorage() method creates a replicationState via replicateRxStorageInstance(), but this local variable is never assigned to this.replicationState:

const replicationState = replicateRxStorageInstance({...});  // Line 375
// ... migration happens ...
await this.cancel();  // Line 474 - but this.replicationState is undefined!

When cancel() runs, it checks if (this.replicationState) which is always undefined, so cancelRxStorageReplication() is never called.

Consequence

The subscriptions created in upstream.ts are never unsubscribed:

• forkInstance.changeStream().subscribe(...) keeps a reference to the old storage
• masterChangeStream$.subscribe(...) also remains active

These subscriptions are only cleaned up when state.events.canceled emits true, which only happens when cancelRxStorageReplication() is called.

Heap Snapshot Evidence

The retainer path shows:

sessionId → docData → previousDocumentData → events → task → Array → openTasks → Context → oldStorage → RxStorageInstanceDexie → changes$ → Subject

This confirms the openTasks array in upstream.ts and the changes$ Subject are being retained.

Environment

• RxDB version: 16.21.1+
• Storage: Dexie (IndexedDB)
• Plugins: RxDBMigrationSchemaPlugin, RxDBLeaderElectionPlugin

Fix

Add one line after creating the replication state in migrateStorage():

const replicationState = replicateRxStorageInstance({...});
this.replicationState = replicationState;  // ADD THIS LINE

This allows cancel() to properly call cancelRxStorageReplication() which emits the cancel event and triggers subscription cleanup.