mysql主備模式介紹｜8月更文挑戰
前置條件
目前已經完成了mysql的主備模式的搭建。mysql
Mysql 主備模式
- STATEMENT模式（SBR） 每一條會修改數據的sql語句會記錄到binlog中。優勢是並不須要記錄每一條sql語句和每一行的數據變化，減小了binlog日誌量，節約IO，提升性能。缺點是在某些狀況下會致使master-slave中的數據不一致(如sleep()函數， last_insert_id()，以及user-defined functions(udf)等會出現問題)
- ROW模式（RBR） 不記錄每條sql語句的上下文信息，僅需記錄哪條數據被修改了，修改爲什麼樣了。並且不會出現某些特定狀況下的存儲過程、或function、或trigger的調用和觸發沒法被正確複製的問題。缺點是會產生大量的日誌，尤爲是alter table的時候會讓日誌暴漲。
- MIXED模式（MBR） 以上兩種模式的混合使用，通常的複製使用STATEMENT模式保存binlog，對於STATEMENT模式沒法複製的操做使用ROW模式保存binlog，MySQL會根據執行的SQL語句選擇日誌保存方式。
查看目前使用的模式
mysql> show global variables like "%binlog_format%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| binlog_format | ROW |
+---------------+-------+
複製代碼
執行一條語句sql
delete from t /*comment*/ where a>=4 and t_modified<='2018-11-10' limit 1;
複製代碼
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000005 | 2847 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
mysql> show binlog events in 'master.000005';
複製代碼
查看binogshell
| mysql-bin.000005 | 2627 | Query | 1 | 2714 | BEGIN |
| mysql-bin.000005 | 2714 | Table_map | 1 | 2768 | table_id: 118 (testKeep.t) |
| mysql-bin.000005 | 2768 | Write_rows | 1 | 2816 | table_id: 118 flags: STMT_END_F |
| mysql-bin.000005 | 2816 | Xid | 1 | 2847 | COMMIT /* xid=1507 */ |
| mysql-bin.000005 | 2847 | Anonymous_Gtid | 1 | 2926 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS'
複製代碼
切換爲MIXED模式並查看效果
爲何要切換爲MIXED模式？數據庫
row模式很是費空間，statement模式由於執行索引不必定相同可能會致使主備不一致問題，由此產生了row格式。因此線上 MySQL 設置的 binlog 格式是 statement 的話，那基本上就能夠認爲這是一個不合理的設置。你至少應該把 binlog 的格式設置爲 mixed。bash
如何切換markdown
vi /etc/my.cnf # 根據自身狀況調整位置
log-bin=mysql-bin
binlog_format=MIXED
mysql> show global variables like "%binlog_format%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| binlog_format | MIXED |
+---------------+-------+
1 row in set (0.01 sec)
複製代碼
並且因爲擁有statement模式的特點，咱們在數據恢復上能夠很方便函數
咱們用測試數據庫testKeep分別測試增、刪、改的恢復方法性能
mysql> select * from t;
+----+------+---------------------+
| id | a | t_modified |
+----+------+---------------------+
| 1 | 1 | 2018-11-13 00:00:00 |
| 2 | 2 | 2018-11-12 00:00:00 |
| 3 | 3 | 2018-11-11 00:00:00 |
| 4 | 4 | 2018-11-10 00:00:00 |
| 7 | 7 | 2018-11-15 00:00:00 |
+----+------+---------------------+
5 rows in set (0.00 sec)
複製代碼
增：測試
mysql> insert into t values(8,8,'2021-6-4');
Query OK, 1 row affected (0.00 sec)
複製代碼
mysql> show binlog events in 'mysql-bin.000007';
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
| mysql-bin.000007 | 4 | Format_desc | 1 | 125 | Server ver: 8.0.25, Binlog ver: 4 |
| mysql-bin.000007 | 125 | Previous_gtids | 1 | 156 | |
| mysql-bin.000007 | 156 | Anonymous_Gtid | 1 | 235 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 235 | Query | 1 | 333 | BEGIN |
| mysql-bin.000007 | 333 | Query | 1 | 462 | use `testKeep`; insert into t values(8,8,'2021-6-4') |
| mysql-bin.000007 | 462 | Xid | 1 | 493 | COMMIT /* xid=58 */ |
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
6 rows in set (0.00 sec)
複製代碼
咱們發現，日誌行數比之前ROW 少特別多，並且完整的記錄了sql語句，能夠根據sql語句對誤增的數據直接刪除。ui
改
mysql> update t set a = 99 where id = 8;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
複製代碼
mysql> show binlog events in 'mysql-bin.000007';
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
| mysql-bin.000007 | 4 | Format_desc | 1 | 125 | Server ver: 8.0.25, Binlog ver: 4 |
| mysql-bin.000007 | 125 | Previous_gtids | 1 | 156 | |
| mysql-bin.000007 | 156 | Anonymous_Gtid | 1 | 235 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 235 | Query | 1 | 333 | BEGIN |
| mysql-bin.000007 | 333 | Query | 1 | 462 | use `testKeep`; insert into t values(8,8,'2021-6-4') |
| mysql-bin.000007 | 462 | Xid | 1 | 493 | COMMIT /* xid=58 */ |
| mysql-bin.000007 | 493 | Anonymous_Gtid | 1 | 572 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 572 | Query | 1 | 671 | BEGIN |
| mysql-bin.000007 | 671 | Query | 1 | 797 | use `testKeep`; update t set a = 99 where id = 8 |
| mysql-bin.000007 | 797 | Xid | 1 | 828 | COMMIT /* xid=69 */ |
+------------------+-----+----------------+-----------+-------------+------------------------------------------------------+
10 rows in set (0.00 sec)
複製代碼
它會修改事件先後的區別，能夠根據這些區別而還原數據
刪
mysql> delete from t where id = 8;
Query OK, 1 row affected (0.01 sec)
複製代碼
mysql> show binlog events in 'mysql-bin.000007';
+------------------+------+----------------+-----------+-------------+------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+------+----------------+-----------+-------------+------------------------------------------------------+
| mysql-bin.000007 | 4 | Format_desc | 1 | 125 | Server ver: 8.0.25, Binlog ver: 4 |
| mysql-bin.000007 | 125 | Previous_gtids | 1 | 156 | |
| mysql-bin.000007 | 156 | Anonymous_Gtid | 1 | 235 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 235 | Query | 1 | 333 | BEGIN |
| mysql-bin.000007 | 333 | Query | 1 | 462 | use `testKeep`; insert into t values(8,8,'2021-6-4') |
| mysql-bin.000007 | 462 | Xid | 1 | 493 | COMMIT /* xid=58 */ |
| mysql-bin.000007 | 493 | Anonymous_Gtid | 1 | 572 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 572 | Query | 1 | 671 | BEGIN |
| mysql-bin.000007 | 671 | Query | 1 | 797 | use `testKeep`; update t set a = 99 where id = 8 |
| mysql-bin.000007 | 797 | Xid | 1 | 828 | COMMIT /* xid=69 */ |
| mysql-bin.000007 | 828 | Anonymous_Gtid | 1 | 907 | SET @@SESSION.GTID_NEXT= 'ANONYMOUS' |
| mysql-bin.000007 | 907 | Query | 1 | 997 | BEGIN |
| mysql-bin.000007 | 997 | Query | 1 | 1108 | use `testKeep`; delete from t where id = 8 |
| mysql-bin.000007 | 1108 | Xid | 1 | 1139 | COMMIT /* xid=88 */ |
+------------------+------+----------------+-----------+-------------+------------------------------------------------------+
14 rows in set (0.00 sec)
複製代碼
很明顯咱們查出了 這條sql被建立以後發生的全部事情，被新增過，修改過，後來又被刪除了。
讀寫分離
從節點開啓只讀模式
set global read_only是全局級別的,置爲1以後root用戶還能夠寫，其餘用戶不能寫
mysql> set global read_only=1;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%read_only%';
+-----------------------+-------+
| Variable_name | Value |
+-----------------------+-------+
| innodb_read_only | OFF |
| read_only | ON |
| super_read_only | OFF |
| transaction_read_only | OFF |
+-----------------------+-------+
複製代碼
#創建只讀帳戶並分配權限
CREATE USER '{帳戶名稱}'@'%' IDENTIFIED BY '{帳戶密碼}';
grant SELECT on *.* to '{帳戶名稱}'@'%';
複製代碼
切換到只讀用戶,並進行測試
mysql> select count(*) from t;
+----------+
| count(*) |
+----------+
| 6 |
+----------+
1 row in set (0.00 sec)
mysql> insert into t values(15,15,'2021-6-4');
ERROR 1290 (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement
mysql> delete from t where id = 2;
ERROR 1290 (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement
mysql> update t set a = 99 where id = 2;
ERROR 1290 (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement
複製代碼
結果顯示能夠查，不能夠增刪改。
參考文章
成文時間比較長（老存貨了），已經找不到參考文獻。
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