| 步驟 | 詳細描述 |
|---|---|
| 保存主節點信息 | 執行slaveof后從節點只保存主節點的地址信息便直接返回 |
| 主從建立socket連接 | 從節點(slave)內部通過每秒運行的定時任務維護復制相關邏輯，當定時任務發現存在新的主節點后，會嘗試與該節點建立網絡連接;從節點會建立一個socket套接字，專門用于接受住節點發送的復制命令；如果從節點無法建立連接，定時任務會無限重試直到連接成功或者執行 slaveof no one 取消復制 |
| 發送ping命令 | 連接建立成功后從節點發送ping請求進行首次通信，ping請求的目的：檢測主從之間套接字是否可用；檢測主節點當前是否可接受處理命令.如果發送ping命令后，從節點沒有收到主節點的pong回復或者超時，比如網絡超時或者主節點正在阻塞無法響應命令，從節點會端口復制連接，下次定時任務會發起重連 |
| 權限驗證 | 如果主節點設置了requirepass 參數，則需要密碼驗證，從節點必須配置masterauth參數保證與主節點相同的密碼才能通過驗證；如果驗證失敗復制將終止，從節點重新發起復制流程 |
| 同步數據集 | 主從復制連接正常通信后，對于首次建立復制的場景，主節點會把持有的數據全部發送給從節點. |
| 命令持續復制 | 當主節點把當前的數據同步給從節點后，變成了復制的建立流程，接下來主節點會持續地把寫命令發送給從節點，保證主從數據一致性 |
127.0.0.1:6381> slaveof 127.0.0.1 6380 Redis5.0.0 改為 ： replicaof masterip> masterport>
6381 啟動
查看info replication
數據同步
| 類型 | 描述 |
|---|---|
| 全量復制 | 一般用于初次復制場景，Redis早期支持的復制功能只有全量復制，它會把主節點全部數據一次性發送給從節點，當數據量較大時，會對主從節點和網絡造成很大的開銷 |
| 部分復制 | 用于處理在主從復制中因網絡閃斷等原因造成的數據丟失場景，當從節點再次連上主節點后，如果條件允許，主節點會補發丟失數據給從節點。因為補發的數據遠遠小于全量數據，可以有效避免全量復制的過高開銷 |
復制偏移量
| 參數 | 描述 |
|---|---|
| master_repl_offset | 參與復制的主從節點都會維護自身復制偏移量。主節點(master)在處理完寫入命令后，會把命令的字節長度做累加記錄，統計信息在info replication中的master_repl_offset指標中 |
| slave0 | 從節點(slave) 每秒鐘上報自身的復制偏移量給主節點，因此主節點也會保存從節點的復制偏移量 |
| slave_repl_offset | 從節點在接收到主節點發送的命令后，也會累加記錄自身的偏移量。 |
復制積壓緩沖區
| 參數 | 描述 |
|---|---|
| repl_backlog_active:1 | 開啟復制緩沖區 |
| repl_backlog_size:1048576 | 緩沖區最大長度 |
| repl_backlog_first_byte_offset:1 | 起始偏移量，計算當前緩沖區可用范圍 |
| repl_backlog_histlen:2301 | 已保存數據的有效長度 |
| master_replid | 主節點實例的master_replid相同 |
| master_replid2 | 未發生切換，即主實例未發生過變化，所以初始值為0 |
psync 命令
從節點使用psync命令完成部分復制和全量復制功能
30227:M 05 Aug 2019 18:52:44.698 * Replica 127.0.0.1:6381 asks for synchronization 30227:M 05 Aug 2019 18:52:44.698 * Partial resynchronization not accepted: Replication ID mismatch (Replica asked for 'e7d71fb600183a175afadbd1354e97edddb2541a', my replication IDs are 'e24f6e42917e7c162ec45a713b0ee3872005ee8b' and '0000000000000000000000000000000000000000')
6381 從節點打印分析
31771:S 06 Aug 2019 12:21:40.213 * DB loaded from disk: 0.000 seconds 31771:S 06 Aug 2019 12:21:40.213 * Before turning into a replica, using my master parameters to synthesize a cached master: I may be able to synchronize with the new master with just a partial transfer. #啟動成功 31771:S 06 Aug 2019 12:21:40.213 * Ready to accept connections # 開始連接主節點 31771:S 06 Aug 2019 12:21:40.214 * Connecting to MASTER 127.0.0.1:6380 # 開始同步 31771:S 06 Aug 2019 12:21:40.214 * MASTER -> REPLICA sync started 31771:S 06 Aug 2019 12:21:40.214 * Non blocking connect for SYNC fired the event. 31771:S 06 Aug 2019 12:21:40.214 * Master replied to PING, replication can continue... # 嘗試增量同步 31771:S 06 Aug 2019 12:21:40.214 * Trying a partial resynchronization (request 668b25f85e84c5900e1032e4b5e1f038f01cfa49:5895). # 全量同步 31771:S 06 Aug 2019 12:21:40.215 * Full resync from master: c88cd043d66193e867929d9d5fadc952954371e5:0 31771:S 06 Aug 2019 12:21:40.215 * Discarding previously cached master state. 31771:S 06 Aug 2019 12:21:40.240 * MASTER -> REPLICA sync: receiving 224 bytes from master 31771:S 06 Aug 2019 12:21:40.241 * MASTER -> REPLICA sync: Flushing old data 31771:S 06 Aug 2019 12:21:40.241 * MASTER -> REPLICA sync: Loading DB in memory 31771:S 06 Aug 2019 12:21:40.241 * MASTER -> REPLICA sync: Finished with success
全量復制
31651:M 06 Aug 2019 11:08:40.802 * Starting BGSAVE for SYNC with target: disk 31651:M 06 Aug 2019 11:08:40.802 * Background saving started by pid 31676 31676:C 06 Aug 2019 11:08:40.805 * DB saved on disk 31676:C 06 Aug 2019 11:08:40.806 * RDB: 0 MB of memory used by copy-on-write 31651:M 06 Aug 2019 11:08:40.886 * Background saving terminated with success 31651:M 06 Aug 2019 11:08:40.886 * Synchronization with replica 127.0.0.1:6381 succeeded
31645:S 06 Aug 2019 11:08:40.886 * MASTER -> REPLICA sync: receiving 224 bytes from master
client-output-buffer-limit replica 256mb 64mb 60
31651:M 06 Aug 2019 11:08:40.886 * Synchronization with replica 127.0.0.1:6381 succeeded
31645:S 06 Aug 2019 11:08:40.886 * MASTER -> REPLICA sync: Flushing old data
31645:S 06 Aug 2019 11:08:40.886 * MASTER -> REPLICA sync: Loading DB in memory 31645:S 06 Aug 2019 11:08:40.886 * MASTER -> REPLICA sync: Finished with success
| 標識 | 含義 |
|---|---|
| M | 當前為主節點日志 |
| S | 當前為從節點日志 |
| C | 子進程日志 |
部分復制
31767:M 06 Aug 2019 14:13:26.096 # Connection with replica 127.0.0.1:6381 lost.
從節點打印： 31934:S 06 Aug 2019 14:20:54.745 * MASTER -> REPLICA sync started 31934:S 06 Aug 2019 14:20:54.745 * Non blocking connect for SYNC fired the event. 31934:S 06 Aug 2019 14:20:54.745 * Master replied to PING, replication can continue... 31934:S 06 Aug 2019 14:20:54.745 * Trying a partial resynchronization (request c88cd043d66193e867929d9d5fadc952954371e5:9996). 31934:S 06 Aug 2019 14:20:54.746 * Successful partial resynchronization with master. 31934:S 06 Aug 2019 14:20:54.746 * MASTER -> REPLICA sync: Master accepted a Partial Resynchronization. 主節點打印： 31767:M 06 Aug 2019 14:21:49.065 * Replica 127.0.0.1:6381 asks for synchronization 31767:M 06 Aug 2019 14:21:49.066 * Partial resynchronization request from 127.0.0.1:6381 accepted. Sending 0 bytes of backlog starting from offset 10066.
31938:S 06 Aug 2019 14:21:49.065 * Trying a partial resynchronization (request c88cd043d66193e867929d9d5fadc952954371e5:10066).
31938:S 06 Aug 2019 14:21:49.066 * Successful partial resynchronization with master. 31938:S 06 Aug 2019 14:21:49.066 * MASTER -> REPLICA sync: Master accepted a Partial Resynchronization.
31767:M 06 Aug 2019 14:21:49.065 * Replica 127.0.0.1:6381 asks for synchronization 31767:M 06 Aug 2019 14:21:49.066 * Partial resynchronization request from 127.0.0.1:6381 accepted. Sending 0 bytes of backlog starting from offset 10066.
心跳
異步復制
讀寫分離
總結
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