Change-Id: I95aa3b678b76cd06439d1feaba7f09a9c13f8931
/**
* Wait for the replica DB to catch up to a given master position
*
+ * Note that this does not start any new transactions. If any existing transaction
+ * is flushed, and this is called, then queries will reflect the point the DB was synced
+ * up to (on success) without interference from REPEATABLE-READ snapshots.
+ *
* @param DBMasterPos $pos
* @param int $timeout The maximum number of seconds to wait for synchronisation
* @return int|null Zero if the replica DB was past that position already,