masterTryPartialResynchronization 函数中的相关代码如下： /* We still have the data our slave is asking for? */ if (!server.repl_backlog || psync_offset < server.repl_backlog_off || psync_offset > (server.repl_backlog_off + server.repl_backlog_histlen)) { serverLog(LL_NOTICE, "Unable to partial resync with replica %s for lack of backlog (Replica request was: %lld).", replicationGetSlaveName(c), psync_offset); if (psync_offset > server.master_repl_offset) { serverLog(LL_WARNING, "Warning: replica %s tried to PSYNC with an offset that is greater than the master replication offset.", replicationGetSlaveName(c)); } goto need_full_resync; } 上面的代码进行了前置判断，如果从节点的读位置对应的数据丢失了，就需要执行全量复制。这种情况不会执行到 addReplyReplicationBacklog 函数中。