MySQL Group Replication / InnoDB Cluster：single-primary vs multi-primary mode 對 transaction certification 的影響MySQL Group Replication 提供 synchronous multi-primary replication、用 Paxos-like Group Communication Engine（GCE）達成 quorum-based commit。但「multi-primary」不是「single-primary 多開幾個 write 入口」、是 *transaction conflict detection + certification* 整個機制不同。本文走 GR 機制（GCE + certification + applier）、single-primary vs multi-primary mode、InnoDB Cluster 跟 MySQL Shell / Router 整合、5 production 踩雷（cert lag / write conflict / large transaction / network partition / member 加入 catch-up）、何時用 GR 何時用傳統 replication