Transaction Reordering in Replicated Databases F.Pedone, R.Guerraoui and A.Schiper This paper presents a fault-tolerant lazy replication protocol that ensures 1-copy serializability at a relatively low cost. Unlike eager replication approaches, our protocol enables local transaction execution and does not lead to any deadlock situation. Compared to previous lazy replication approaches, we significantly reduce the abort rate of transactions and we do not require any reconciliation procedure. Our protocol first executes transactions locally, then broadcasts a transaction certification message to all replica managers, and finally employs a certification procedure to ensure 1-copy serializability. Certification messages are broadcast using a non-blocking atomic broadcast primitive, which alleviates the need for a more expensive non-blocking atomic commitment algorithm. The certification procedure uses a reordering technique to reduce the probability of transaction aborts.