本篇文章給大家?guī)砹岁P(guān)于mysql的相關(guān)知識，其中主要介紹了關(guān)于mysql復制技術(shù)的相關(guān)問題，包括了異步復制、半同步復制等等內(nèi)容，下面一起來看一下，希望對大家有幫助。
推薦學習：mysql
異步復制
在異步復制（async replication）中，Master不用關(guān)心Slave是否接收到二進制日志，所以Master與Slave沒有任何的依賴關(guān)系。你可以認為Master和Slave是分別獨自工作的兩臺服務器，數(shù)據(jù)最終會通過二進制日志達到一致。
異步復制的性能最好，因為它對數(shù)據(jù)庫本身幾乎沒有任何開銷，除非主從延遲非常大，Dump Thread需要讀取大量二進制日志文件。
如果業(yè)務對于數(shù)據(jù)一致性要求不高，當發(fā)生故障時，能容忍數(shù)據(jù)的丟失，甚至大量的丟失，推薦用異步復制，這樣性能最好（比如像微博這樣的業(yè)務，雖然它對性能的要求極高，但對于數(shù)據(jù)丟失，通常可以容忍）。但往往核心業(yè)務系統(tǒng)最關(guān)心的就是數(shù)據(jù)安全，比如監(jiān)控業(yè)務、告警系統(tǒng)。
異步復制環(huán)境的規(guī)劃：
-
master（docker），端口3310
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slave（docker），端口3311
master的配置
配置文件my.cnf
$?sudo?cat?/home/mysql/docker-data/3311/conf/my.cnf #?For?advice?on?how?to?change?settings?please?see #?http://dev.mysql.com/doc/refman/5.7/en/server-configuration-defaults.html [mysqld] # #?Remove?leading?#?and?set?to?the?amount?of?RAM?for?the?most?important?data #?cache?in?MySQL.?Start?at?70%?of?total?RAM?for?dedicated?server,?else?10%. #?innodb_buffer_pool_size?=?128M # #?Remove?leading?#?to?turn?on?a?very?important?data?integrity?option:?logging #?changes?to?the?binary?log?between?backups. #?log_bin # #?Remove?leading?#?to?set?options?mainly?useful?for?reporting?servers. #?The?server?defaults?are?faster?for?transactions?and?fast?SELECTs. #?Adjust?sizes?as?needed,?experiment?to?find?the?optimal?values. #?join_buffer_size?=?128M #?sort_buffer_size?=?2M #?read_rnd_buffer_size?=?2M #datadir=/home/mysql/docker-data/3307/data #socket=/home/mysql/docker-data/3307/mysql.sock character_set_server=utf8 init_connect='SET?NAMES?utf8' #?Disabling?symbolic-links?is?recommended?to?prevent?assorted?security?risks symbolic-links=0 #log-error=/home/mysql/docker-data/3307/logs/mysqld.log #pid-file=/home/mysql/docker-data/3307/mysqld.pid lower_case_table_names=1?#?表名是否小寫 server-id=1403311 log-bin=mysql-bin?#?開啟binlog binlog-format=ROW?#?binlog的格式 auto_increment_increment=1?#?自增的步長，適用于主主復制，為了避免id沖突，步長設置為master的個數(shù) auto_increment_offset=1?#?自增的偏移，主主復制每個master的偏移需要不一致 #?binlog-do-db=mstest??????#?要同步的數(shù)據(jù)庫 #?binlog-ignore-db=mysql??#?要忽略的數(shù)據(jù)庫 #rpl_semi_sync_master_enabled=1 #rpl_semi_sync_master_timeout=10000
啟動mysql：
$?docker?run?--name?mysql3310?-p?3310:3306?--privileged=true?-ti?-e?MYSQL_ROOT_PASSWORD=root?-e?MYSQL_DATABASE=order?-e?MYSQL_USER=user?-e?MYSQL_PASSWORD=pass?-v?/home/mysql/docker-data/3310/conf:/etc/mysql/conf.d?-v?/home/mysql/docker-data/3310/data/:/var/lib/mysql?-v?/home/mysql/docker-data/3310/logs/:/var/log/mysql?-d?mysql:5.7
創(chuàng)建用于同步的用戶：
mysql>?GRANT?REPLICATION?SLAVE,FILE,REPLICATION?CLIENT?ON?*.*?TO?'repluser'@'%'?IDENTIFIED?BY?'123456'; Query?OK,?0?rows?affected,?1?warning?(0.01?sec) mysql>?FLUSH?PRIVILEGES; Query?OK,?0?rows?affected?(0.01?sec)
在master上查看master的二進制日志：
mysql>?show?master?status; +------------------+----------+--------------+------------------+-------------------+ |?File?????????????|?Position?|?Binlog_Do_DB?|?Binlog_Ignore_DB?|?Executed_Gtid_Set?| +------------------+----------+--------------+------------------+-------------------+ |?mysql-bin.000003?|??????1147?|??????????????|??????????????????|???????????????????| +------------------+----------+--------------+------------------+-------------------+ 1?row?in?set?(0.00?sec)
查看master上的進程列表：
mysql>?show?processlist; +----+----------+------------------+-------+-------------+------+---------------------------------------------------------------+------------------+ |?Id?|?User?????|?Host?????????????|?db????|?Command?????|?Time?|?State?????????????????????????????????????????????????????????|?Info?????????????| +----+----------+------------------+-------+-------------+------+---------------------------------------------------------------+------------------+ |??2?|?root?????|?localhost????????|?order?|?Query???????|????0?|?starting??????????????????????????????????????????????????????|?show?processlist?| |??6?|?repluser?|?172.17.0.1:48450?|?NULL??|?Binlog?Dump?|??448?|?Master?has?sent?all?binlog?to?slave;?waiting?for?more?updates?|?NULL?????????????| +----+----------+------------------+-------+-------------+------+---------------------------------------------------------------+------------------+ 2?rows?in?set?(0.00?sec)
slave的配置
配置文件my.cnf與master的配置一致，除了server-id字段需唯一。
啟動mysql：
$ docker run --name mysql3311 -p 3311:3306 --privileged=true -ti -e MYSQL_ROOT_PASSWORD=root -e MYSQL_DATABASE=order -e MYSQL_USER=user -e MYSQL_PASSWORD=pass -v /home/mysql/docker-data/3311/conf:/etc/mysql/conf.d -v /home/mysql/docker-data/3311/data/:/var/lib/mysql -v /home/mysql/docker-data/3311/logs/:/var/log/mysql -d mysql:5.7
在slave中設置master的信息：
# master_log_file和master_log_pos取上面show master status顯示的值mysql> change master to master_host='172.23.252.98',master_port=3310,master_user='repluser',master_password='123456',master_log_file='mysql-bin.000003',master_log_pos=1147;
開啟slave，啟動SQL和IO線程：
mysql> start slave;Query OK, 0 rows affected (0.00 sec)
查看slave的狀態(tài)：
mysql> show slave statusG;*************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.54.214 Master_User: repluser Master_Port: 3310 Connect_Retry: 60 Master_Log_File: mysql-bin.000003 Read_Master_Log_Pos: 1147 Relay_Log_File: 2da789531bf3-relay-bin.000002 Relay_Log_Pos: 320 Relay_Master_Log_File: mysql-bin.000003 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 1147 Relay_Log_Space: 534 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 1403311 Master_UUID: cd2eaa0a-7a59-11ec-b3b4-0242ac110002 Master_Info_File: /var/lib/mysql/master.info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version:1 row in set (0.00 sec)
只有新增的數(shù)據(jù)才會進行復制，存量的數(shù)據(jù)需要手動使用工具（如mysqldump）進行同步。
查看slave上的進程列表：
mysql> show processlist; +----+-------------+-----------+-------+---------+------+--------------------------------------------------------+------------------+ | Id | User | Host | db | Command | Time | State | Info | +----+-------------+-----------+-------+---------+------+--------------------------------------------------------+------------------+ | 4 | root | localhost | order | Query | 0 | starting | show processlist | | 7 | system user | | NULL | Connect | 533 | Waiting for master to send event | NULL | | 8 | system user | | NULL | Connect | 127 | Slave has read all relay log; waiting for more updates | NULL | +----+-------------+-----------+-------+---------+------+--------------------------------------------------------+------------------+ 3 rows in set (0.00 sec)
半同步復制
半同步復制是MySQL 5.7版本前的半同步復制機制。
半同步復制要求Master事務提交過程中，至少有N個Slave接收到二進制日志，這樣就能保證當Master發(fā)生宕機，至少有N 臺Slave服務器中的數(shù)據(jù)是完整的。
半同步復制并不是MySQL內(nèi)置的功能，而是要安裝半同步插件，并啟用半同步復制功能，設置N個Slave接受二進制日志成功。
缺點：假設user1在主庫插入了一條數(shù)據(jù)，正在等待數(shù)據(jù)返回，user2這時就能查詢到這條數(shù)據(jù)了，如果此時master掛了，user2又查不到這條數(shù)據(jù)了，產(chǎn)生了類似幻讀的現(xiàn)象。
增強半同步復制
增強半同步復制解決了半同步復制的缺點，WAIT和ACK發(fā)生在事務提交之前，這樣即便Slave沒有收到二進制日志，但是 Master宕機了，由于最后一個事務還沒有提交，所以本身這個數(shù)據(jù)對外也不可見，不存在丟失的問題。
所以，對于任何有數(shù)據(jù)一致性要求的業(yè)務，如電商的核心訂單業(yè)務、銀行、保險、證券等與資金密切相關(guān)的業(yè)務，務必使用增強半同步復制。這樣數(shù)據(jù)才是安全的、有保障的、即使發(fā)生宕機，從機也有一份完整的數(shù)據(jù)。
增強半同步復制環(huán)境是基于異步復制的基礎上進行的。
安裝插件，建議master和slave都安裝，因為會有主從切換的情景：
#?master mysql>?install?plugin?rpl_semi_sync_master?soname?'semisync_master.so'; #?slave mysql>?install?plugin?rpl_semi_sync_slave?soname?'semisync_slave.so';
確保插件安裝成功：
mysql>?show?plugins; ...?... |?rpl_semi_sync_master???????|?ACTIVE???|?REPLICATION????????|?semisync_master.so?|?GPL?????| |?rpl_semi_sync_slave????????|?ACTIVE???|?REPLICATION????????|?semisync_slave.so??|?GPL?????| +----------------------------+----------+--------------------+--------------------+---------+ 46?rows?in?set?(0.00?sec)
先啟動slave上的半同步：
mysql>?set?global?rpl_semi_sync_slave_enabled?=?{0|1};??#?1：啟用，0：禁止
再啟動master上的半同步：
mysql>?set?global?rpl_semi_sync_master_enabled?=?{0|1};??#?1：啟用，0：禁止 #?mysql>?set?global?rpl_semi_sync_master_timeout?=?10000;????#?單位為ms，默認為10s
從庫重啟io_thread：
mysql> stop slave io_thread; mysql> start slave io_thread;
半同步的參數(shù)為什么不建議寫入配置文件
參數(shù)寫入配置文件的話，會使實例啟動后立即進入半同步模式，如果發(fā)生長時間斷連的實例重新運行啟動，有可能導致主庫被拖垮。
長時間斷開的從庫，重新連接后，要等待追完全部事務后，手動開啟半同步模式，而不是啟動后直接切換，防止沖擊主庫。
查詢主庫狀態(tài)信息
mysql> show global status like "%semi%"; +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | Rpl_semi_sync_master_clients | 0 | | Rpl_semi_sync_master_net_avg_wait_time | 0 | | Rpl_semi_sync_master_net_wait_time | 0 | | Rpl_semi_sync_master_net_waits | 0 | | Rpl_semi_sync_master_no_times | 0 | | Rpl_semi_sync_master_no_tx | 0 | | Rpl_semi_sync_master_status | ON | | Rpl_semi_sync_master_timefunc_failures | 0 | | Rpl_semi_sync_master_tx_avg_wait_time | 0 | | Rpl_semi_sync_master_tx_wait_time | 0 | | Rpl_semi_sync_master_tx_waits | 0 | | Rpl_semi_sync_master_wait_pos_backtraverse | 0 | | Rpl_semi_sync_master_wait_sessions | 0 | | Rpl_semi_sync_master_yes_tx | 0 | | Rpl_semi_sync_slave_status | ON | +--------------------------------------------+-------+ 15 rows in set (0.00 sec)
重要參數(shù)說明：
- Rpl_semi_sync_master_clients：支持和注冊半同步復制的已連Slave數(shù)
- Rpl_semi_sync_master_no_times：master關(guān)閉半同步復制的次數(shù)
- Rpl_semi_sync_master_no_tx：master沒有收到slave的回復而提交的次數(shù)，可以理解為master等待超時的次數(shù)，即半同步模式不成功提交數(shù)量
- Rpl_semi_sync_master_status：ON是活動狀態(tài)（半同步），OFF是非活動狀態(tài)（異步），用于表示主服務器使用的是異步復制模式，還是半同步復制模式
- Rpl_semi_sync_master_tx_avg_wait_time：master花在每個事務上的平均等待時間
- Rpl_semi_sync_master_tx_waits：master等待成功的次數(shù)，即master沒有等待超時的次數(shù)，也就是成功提交的次數(shù)
- Rpl_semi_sync_master_yes_tx：master成功接收到slave的回復的次數(shù)，即半同步模式成功提交數(shù)量。
查詢主庫參數(shù)信息
mysql> show global variables like '%sync%'; +-------------------------------------------+------------+ | Variable_name | Value | +-------------------------------------------+------------+ | binlog_group_commit_sync_delay | 0 | | binlog_group_commit_sync_no_delay_count | 0 | | innodb_flush_sync | ON | | innodb_sync_array_size | 1 | | innodb_sync_spin_loops | 30 | | rpl_semi_sync_master_enabled | ON | | rpl_semi_sync_master_timeout | 10000 | | rpl_semi_sync_master_trace_level | 32 | | rpl_semi_sync_master_wait_for_slave_count | 1 | | rpl_semi_sync_master_wait_no_slave | ON | | rpl_semi_sync_master_wait_point | AFTER_SYNC | | rpl_semi_sync_slave_enabled | ON | | rpl_semi_sync_slave_trace_level | 32 | | sync_binlog | 1 | | sync_frm | ON | | sync_master_info | 10000 | | sync_relay_log | 10000 | | sync_relay_log_info | 10000 | +-------------------------------------------+------------+ 18 rows in set (0.01 sec)
重要參數(shù)說明：
- rpl_semi_sync_master_enabled：（主庫）是否啟動半同步
- rpl_semi_sync_master_timeout：等待多時毫秒后變成異步復制，默認是10000ms
- rpl_semi_sync_master_wait_point：5.7默認AFTER_SYNC（增強版半同步復制，無損復制模式），在得到slave的應答后再commit，可選值AFTER_COMMIT，在master提交后同步數(shù)據(jù)給slave，然后master等待slave應答，應答成功返回客戶端。
可以在slave端執(zhí)行stop slave，測試master端會發(fā)生什么情況？
在master上執(zhí)行下面的sql：
mysql> insert into t_order values(3,"C");Query OK, 1 row affected (10.05 sec)
會發(fā)現(xiàn)這條語句會阻塞10s（對應上面的參數(shù)rpl_semi_sync_master_timeout），然后執(zhí)行成功，最后看看看master的日志描述：
2022-01-25T02:31:57.016430Z 4 [Note] Start binlog_dump to master_thread_id(4) slave_server(1403312), pos(mysql-bin.000005, 154) 2022-01-25T02:31:57.016515Z 4 [Note] Start asynchronous binlog_dump to slave (server_id: 1403312), pos(mysql-bin.000005, 154) 2022-01-25T02:33:32.183819Z 2 [Note] Semi-sync replication initialized for transactions. 2022-01-25T02:33:32.183865Z 2 [Note] Semi-sync replication enabled on the master. 2022-01-25T02:33:32.184004Z 0 [Note] Starting ack receiver thread 2022-01-25T02:33:59.644444Z 5 [Note] While initializing dump thread for slave with UUID <aba2eb12-7cbc-11ec-9c1d-0242ac110003>, found a zombie dump thread with the same UUID. Master is killing the zombie dump thread(4). 2022-01-25T02:33:59.644612Z 5 [Note] Start binlog_dump to master_thread_id(5) slave_server(1403312), pos(mysql-bin.000005, 154) 2022-01-25T02:33:59.644632Z 4 [Note] Stop asynchronous binlog_dump to slave (server_id: 1403312) 2022-01-25T02:33:59.644727Z 5 [Note] Start semi-sync binlog_dump to slave (server_id: 1403312), pos(mysql-bin.000005, 154) 2022-01-25T02:38:02.847879Z 0 [ERROR] mysqld: Got an error reading communication packets 2022-01-25T02:38:27.228952Z 2 [Warning] Timeout waiting for reply of binlog (file: mysql-bin.000005, pos: 684), semi-sync up to file mysql-bin.000005, position 419. 2022-01-25T02:38:27.229063Z 2 [Note] Semi-sync replication switched OFF. 2022-01-25T02:39:47.230189Z 5 [Note] Stop semi-sync binlog_dump to slave (server_id: 1403312)
可以發(fā)現(xiàn)半同步關(guān)閉了，變成異步模式。
推薦學習：mysql
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