f Update migrate_deprecated_spendable_outputs docs

Author: tnull

src/io/utils.rs

@@ -230,7 +230,18 @@ pub(crate) fn read_output_sweeper<K: KVStore + Send + Sync>(
 	})
 }
 
-/// Read previously persisted spendable output information from the store.
+/// Read previously persisted spendable output information from the store and migrate to the
+/// upstreamed `OutputSweeper`.
+///
+/// We first iterate all `DeprecatedSpendableOutputInfo`s and have them tracked by the new
+/// `OutputSweeper`. In order to be certain the initial output spends will happen in a single
+/// transaction (and safe on-chain fees), we batch them to happen at current height plus two
+/// blocks. Lastly, we remove the previously persisted data once we checked they are tracked and
+/// awaiting their initial spend at the correct height.
+///
+/// Note that this migration will be run in the `Builder`, i.e., at the time when the migration is
+/// happening no background sync is ongoing, so we shouldn't have a risk of interleaving block
+/// connections during the migration.
 pub(crate) fn migrate_deprecated_spendable_outputs<K: KVStore + Sync + Send, L: Deref>(
 	sweeper: Arc<Sweeper<K>>, kv_store: Arc<K>, logger: L,
 ) -> Result<(), std::io::Error>