主從半同步復制是目前用得最多的MySQL復制方案,日常作業中我們一般通過show slave status陳述句查看當前復制程序中狀態資訊,基本上能滿足大多數場景下的需求,Performance_schema中提供了16個關于復制的監控表(包括組復制、過濾復制等,這里我們先不討論),show slave status中的大多數資訊都來自Performance_schema中的復制系串列,這些表有利于更好的收集主從復制中的狀態,報錯,配置等資訊,并且比show slave status提供了更全面的主從復制的診斷資訊,這些表主要可以分為兩類,分別為IO行程和SQL行程的資訊:

replication_connection_configuration
這張表主要顯示了從庫連接到主庫的配置引數,包括復制用戶、主庫地址、埠等,隨著change master to命令陳述句改變,
replication_connection_status
主要包括當前IO執行緒的狀態資訊,IO執行緒相關錯誤資訊,relaylog中上個排隊和當前正在排隊的事務資訊,當因為連接失敗等問題導致IO行程停止時,可以通過這張表排查錯誤資訊,
mysql> select * from performance_schema.replication_connection_status\G *************************** 1. row *************************** CHANNEL_NAME: GROUP_NAME: SOURCE_UUID: c8e82820-16c4-11ed-8677-005056b65258 THREAD_ID: 341 SERVICE_STATE: ON COUNT_RECEIVED_HEARTBEATS: 67076 LAST_HEARTBEAT_TIMESTAMP: 2023-04-27 15:20:29.393141 RECEIVED_TRANSACTION_SET: c8e82820-16c4-11ed-8677-005056b65258:12-37 LAST_ERROR_NUMBER: 0 LAST_ERROR_MESSAGE: LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000 LAST_QUEUED_TRANSACTION: c8e82820-16c4-11ed-8677-005056b65258:37 LAST_QUEUED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2023-04-26 14:37:27.673466 LAST_QUEUED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2023-04-26 14:37:27.673466 LAST_QUEUED_TRANSACTION_START_QUEUE_TIMESTAMP: 2023-04-26 14:40:51.513510 LAST_QUEUED_TRANSACTION_END_QUEUE_TIMESTAMP: 2023-04-26 14:40:51.513521 QUEUEING_TRANSACTION: QUEUEING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 QUEUEING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 QUEUEING_TRANSACTION_START_QUEUE_TIMESTAMP: 0000-00-00 00:00:00.000000 1 row in set (0.00 sec)
replication_applier_configuration
這個表包含影響從庫回放事務的配置引數,比如REQUIRE_TABLE_PRIMARY_KEY_CHECK(開啟主鍵校驗)、DESIRED_DELAY(延遲復制配置),
replication_applier_status
這個表顯示從庫SQL執行緒的狀態總資訊,現在生產中一般都開啟了多執行緒復制,多執行緒復制下SQL執行緒狀態主要看replication_applier_status_by_coordinator table 和replication_applier_status_by_worker這兩張表,
replication_applier_status_by_coordinator
對于多執行緒復制,從庫使用了多個復制執行緒(work thread),并且開啟了一個協調執行緒(coordinator thread)來管理它們,這個表顯示了協調執行緒的狀態資訊和錯誤資訊,并且包括上一個被協調執行緒buffer的事務,以及當前協調執行緒正在buffer的事務,在多執行緒復制中,首先由協調執行緒從relaylog中讀取并快取需要執行事務,然后再把事務分配給其中一個復制執行緒,
mysql> select * from performance_schema.replication_applier_status_by_coordinator\G *************************** 1. row *************************** CHANNEL_NAME: THREAD_ID: 342 SERVICE_STATE: ON LAST_ERROR_NUMBER: 0 LAST_ERROR_MESSAGE: LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000 LAST_PROCESSED_TRANSACTION: c8e82820-16c4-11ed-8677-005056b65258:37 LAST_PROCESSED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2023-04-26 14:37:27.673466 LAST_PROCESSED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2023-04-26 14:37:27.673466 LAST_PROCESSED_TRANSACTION_START_BUFFER_TIMESTAMP: 2023-04-26 14:42:29.097360 LAST_PROCESSED_TRANSACTION_END_BUFFER_TIMESTAMP: 2023-04-26 14:42:29.098834 PROCESSING_TRANSACTION: PROCESSING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 PROCESSING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 PROCESSING_TRANSACTION_START_BUFFER_TIMESTAMP: 0000-00-00 00:00:00.000000 1 row in set (0.00 sec)
replication_applier_status_by_worker
這個表顯示了多執行緒復制中從庫各個回放執行緒(applier thread)的狀態及錯誤資訊,applier thread也稱workers,如果從庫SQL執行緒在回放事務中報錯,需要查詢這個表獲取詳細的報錯資訊,如下圖所示,下面的報錯顯示了SQL執行緒在回放事務程序中由于notest表中的某條記錄不存在導致寫入失敗:
mysql> select * from performance_schema.replication_applier_status_by_worker where last_error_message != ''\G *************************** 1. row *************************** CHANNEL_NAME: WORKER_ID: 1 THREAD_ID: NULL SERVICE_STATE: OFF LAST_ERROR_NUMBER: 1032 LAST_ERROR_MESSAGE: Worker 1 failed executing transaction 'c8e82820-16c4-11ed-8677-005056b65258:38' at master log bin.000012, end_log_pos 3315; Could not execute Update_rows event on table test.notest; Can't find record in 'notest', Error_code: 1032; handler error HA_ERR_KEY_NOT_FOUND; the event's master log FIRST, end_log_pos 3315 LAST_ERROR_TIMESTAMP: 2023-04-28 09:45:59.684586 LAST_APPLIED_TRANSACTION: LAST_APPLIED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 LAST_APPLIED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000 LAST_APPLIED_TRANSACTION_START_APPLY_TIMESTAMP: 0000-00-00 00:00:00.000000 LAST_APPLIED_TRANSACTION_END_APPLY_TIMESTAMP: 0000-00-00 00:00:00.000000 APPLYING_TRANSACTION: c8e82820-16c4-11ed-8677-005056b65258:38 APPLYING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2023-04-28 09:45:59.673804 APPLYING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2023-04-28 09:45:59.673804 APPLYING_TRANSACTION_START_APPLY_TIMESTAMP: 2023-04-28 09:45:59.684183 LAST_APPLIED_TRANSACTION_RETRIES_COUNT: 0 LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0 LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE: LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000 APPLYING_TRANSACTION_RETRIES_COUNT: 0 APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0 APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE: APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000 1 row in set (0.00 sec)
mysql.slave_master_info
此外mysql.slave_master_info這個表也需要注意,這個表顯示了復制用戶的明文密碼,因此需要注意兩點:
1.不要給復制用戶repl授予除了REPLICATION SLAVE以外的權限,防止被獲取明文密碼后,利用這個用戶進行一些高危操作,
2.在給資料庫重建主從復制或者新加從庫時,如果忘記了復制用戶的密碼,不需要再重置,可以通過這個表獲取,
mysql> select * from mysql.slave_master_info\G *************************** 1. row *************************** Number_of_lines: 33 Master_log_name: bin.000012 Master_log_pos: 197 Host: 10.3.111.102 User_name: repl User_password: PASSW0RD Port: 3306 Connect_retry: 60 Enabled_ssl: 0 Ssl_ca: Ssl_capath: Ssl_cert: Ssl_cipher: Ssl_key: Ssl_verify_server_cert: 0 Heartbeat: 30 Bind: Ignored_server_ids: 0 Uuid: c8e82820-16c4-11ed-8677-005056b65258 Retry_count: 86400 Ssl_crl: Ssl_crlpath: Enabled_auto_position: 1 Channel_name: Tls_version: Public_key_path: Get_public_key: 0 Network_namespace: Master_compression_algorithm: uncompressed Master_zstd_compression_level: 3 Tls_ciphersuites: NULL Source_connection_auto_failover: 0 Gtid_only: 0
總結一下,show slave status已經是一個比較全面的監控了,其他用的比較多的performance_schema中的關于復制的表有replication_applier_status_by_worker、The replication_applier_status_by_coordinator、replication_connection_status,作業中需要注意結合這些表的使用更好的排查問題,
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