mysql8的介紹與特性

mysql8(新特性)

1. 默認字符集由latin1變爲utf8mb4

在8.0版本之前,默認字符集爲latin1,utf8指向的是utf8mb3,8.0版本默認字符集爲utf8mb4,utf8默認指向的也是utf8mb4。
注:在Percona Server 8.0.15版本上測試,utf8仍然指向的是utf8mb3,與官方文檔有出入。

2. MyISAM系統表全部換成InnoDB表

系統表全部換成事務型的innodb表,默認的MySQL實例將不包含任何MyISAM表,除非手動創建MyISAM表。

3. 自增變量持久化

在8.0之前的版本,自增主鍵AUTO_INCREMENT的值如果大於max(primary key)+1,在MySQL重啓後,會重置AUTO_INCREMENT=max(primary key)+1,這種現象在某些情況下會導致業務主鍵衝突或者其他難以發現的問題。自增主鍵重啓重置的問題很早就被發現(https://bugs.mysql.com/bug.php?id=199),一直到8.0才被解決,8.0版本將會對AUTO_INCREMENT值進行持久化,MySQL重啓後,該值將不會改變。

4. DDL原子化

InnoDB表的DDL支持事務完整性,要麼成功要麼回滾,將DDL操作回滾日誌寫入到data dictionary 數據字典表 mysql.innodb_ddl_log 中用於回滾操作,該表是隱藏的表,通過show tables無法看到。通過設置參數,可將ddl操作日誌打印輸出到mysql錯誤日誌中。

mysql> set global log_error_verbosity=3;
mysql> set global innodb_print_ddl_logs=1;
mysql> create table t1(c int) engine=innodb;
 
# MySQL錯誤日誌:
2018-06-26T11:25:25.817245+08:00 44 [Note] [MY-012473] [InnoDB] InnoDB: DDL log insert : [DDL record: DELETE SPACE, id=41, thread_id=44, space_id=6, old_file_path=./db/t1.ibd]
2018-06-26T11:25:25.817369+08:00 44 [Note] [MY-012478] [InnoDB] InnoDB: DDL log delete : by id 41
2018-06-26T11:25:25.819753+08:00 44 [Note] [MY-012477] [InnoDB] InnoDB: DDL log insert : [DDL record: REMOVE CACHE, id=42, thread_id=44, table_id=1063, new_file_path=db/t1]
2018-06-26T11:25:25.819796+08:00 44 [Note] [MY-012478] [InnoDB] InnoDB: DDL log delete : by id 42
2018-06-26T11:25:25.820556+08:00 44 [Note] [MY-012472] [InnoDB] InnoDB: DDL log insert : [DDL record: FREE, id=43, thread_id=44, space_id=6, index_id=140, page_no=4]
2018-06-26T11:25:25.820594+08:00 44 [Note] [MY-012478] [InnoDB] InnoDB: DDL log delete : by id 43
2018-06-26T11:25:25.825743+08:00 44 [Note] [MY-012485] [InnoDB] InnoDB: DDL log post ddl : begin for thread id : 44
2018-06-26T11:25:25.825784+08:00 44 [Note] [MY-012486] [InnoDB] InnoDB: DDL log post ddl : end for thread id : 44

來看另外一個例子,庫裏只有一個t1表,drop table t1,t2; 試圖刪除t1,t2兩張表,在5.7中,執行報錯,但是t1表被刪除,在8.0中執行報錯,但是t1表沒有被刪除,證明了8.0 DDL操作的原子性,要麼全部成功,要麼回滾。

5. 參數修改持久化

MySQL 8.0版本支持在線修改全局參數並持久化,通過加上PERSIST關鍵字,可以將修改的參數持久化到新的配置文件(mysqld-auto.cnf)中,重啓MySQL時,可以從該配置文件獲取到最新的配置參數。
例如執行:
set PERSIST expire_logs_days=10 ;
系統會在數據目錄下生成一個包含json格式的 mysqld-auto.cnf 的文件,格式化後如下所示,當 my.cnf 和 mysqld-auto.cnf 同時存在時,後者具有更高優先級。

{
    "Version": 1,
    "mysql_server": {
        "expire_logs_days": {
            "Value": "10",
            "Metadata": {
                "Timestamp": 1529657078851627,
                "User": "root",
                "Host": "localhost"
            }
        }
    }
}

6. 新增降序索引

MySQL在語法上很早就已經支持降序索引,但實際上創建的仍然是升序索引,如下MySQL 5.7 所示,c2字段降序,但是從show create table看c2仍然是升序。8.0可以看到,c2字段降序。

# MySQL 5.7
mysql> create table t1(c1 int,c2 int,index idx_c1_c2(c1,c2 desc));
Query OK, 0 rows affected (0.03 sec)
mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  KEY `idx_c1_c2` (`c1`,`c2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)
 
# MySQL 8.0
mysql> create table t1(c1 int,c2 int,index idx_c1_c2(c1,c2 desc));
Query OK, 0 rows affected (0.06 sec)
mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  KEY `idx_c1_c2` (`c1`,`c2` DESC)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC
1 row in set (0.00 sec)

再來看看降序索引在執行計劃中的表現,在t1表插入10萬條隨機數據,查看select * from t1 order by c1 , c2 desc;的執行計劃。從執行計劃上可以看出,5.7的掃描數100113遠遠大於8.0的5行,並且使用了filesort。

DELIMITER ;;
CREATE PROCEDURE test_insert ()
BEGIN
DECLARE i INT DEFAULT 1;
WHILE i<100000
DO
insert into t1 select rand()*100000, rand()*100000;
SET i=i+1;
END WHILE ;
commit;
END;;
DELIMITER ;
CALL test_insert();
 
# MySQL 5.7
mysql> explain select * from t1 order by c1 , c2 desc limit 5;
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows   | filtered | Extra                       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL | 100113 |   100.00 | Using index; Using filesort |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
1 row in set, 1 warning (0.00 sec)
 
# MySQL 8.0
mysql> explain select * from t1 order by c1 , c2 desc limit 5;
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    5 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

降序索引只是對查詢中特定的排序順序有效,如果使用不當,反而查詢效率更低,比如上述查詢排序條件改爲 order by c1 desc, c2 desc,這種情況下,5.7的執行計劃要明顯好於8.0的,如下:

# MySQL 5.7
mysql> explain select * from t1  order by c1 desc , c2 desc limit 5;
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    5 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.01 sec)
 
# MySQL 8.0
mysql> explain select * from t1 order by c1 desc , c2 desc limit 5;
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows   | filtered | Extra                       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL | 100429 |   100.00 | Using index; Using filesort |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+--------+----------+-----------------------------+
1 row in set, 1 warning (0.01 sec)

7. group by 不再隱式排序

mysql 8.0 對於group by 字段不再隱式排序,如需要排序,必須顯式加上order by 子句。

# 表結構
mysql> show create table tb1\G
*************************** 1. row ***************************
       Table: tb1
Create Table: CREATE TABLE `tb1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `group_own` int(11) DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC
1 row in set (0.00 sec)
 
# 表數據
mysql> select * from tb1;
+----+------+-----------+
| id | name | group_own |
+----+------+-----------+
|  1 | 1    |         0 |
|  2 | 2    |         0 |
|  3 | 3    |         0 |
|  4 | 4    |         0 |
|  5 | 5    |         5 |
|  8 | 8    |         1 |
| 10 | 10   |         5 |
+----+------+-----------+
7 rows in set (0.00 sec)
 
# MySQL 5.7
mysql> select count(id), group_own from tb1 group by group_own;
+-----------+-----------+
| count(id) | group_own |
+-----------+-----------+
|         4 |         0 |
|         1 |         1 |
|         2 |         5 |
+-----------+-----------+
3 rows in set (0.00 sec)
 
# MySQL 8.0.11
mysql> select count(id), group_own from tb1 group by group_own;
+-----------+-----------+
| count(id) | group_own |
+-----------+-----------+
|         4 |         0 |
|         2 |         5 |
|         1 |         1 |
+-----------+-----------+
3 rows in set (0.00 sec)
 
# MySQL 8.0.11顯式地加上order by進行排序
mysql> select count(id), group_own from tb1 group by group_own order by group_own;
+-----------+-----------+
| count(id) | group_own |
+-----------+-----------+
|         4 |         0 |
|         1 |         1 |
|         2 |         5 |
+-----------+-----------+
3 rows in set (0.00 sec)

8. JSON特性增強

MySQL 8 大幅改進了對 JSON 的支持,添加了基於路徑查詢參數從 JSON 字段中抽取數據的 JSON_EXTRACT() 函數,以及用於將數據分別組合到 JSON 數組和對象中的 JSON_ARRAYAGG() 和 JSON_OBJECTAGG() 聚合函數。

在主從複製中,新增參數 binlog_row_value_options,控制JSON數據的傳輸方式,允許對於Json類型部分修改,在binlog中只記錄修改的部分,減少json大數據在只有少量修改的情況下,對資源的佔用。

9. redo & undo 日誌加密

增加以下兩個參數,用於控制redo、undo日誌的加密。
innodb_undo_log_encrypt
innodb_undo_log_encrypt

10. innodb select for update跳過鎖等待

select ... for update,select ... for share(8.0新增語法) 添加 NOWAIT、SKIP LOCKED語法,跳過鎖等待,或者跳過鎖定。
在5.7及之前的版本,select...for update,如果獲取不到鎖,會一直等待,直到innodb_lock_wait_timeout超時。

在8.0版本,通過添加nowait,skip locked語法,能夠立即返回。如果查詢的行已經加鎖,那麼nowait會立即報錯返回,而skip locked也會立即返回,只是返回的結果中不包含被鎖定的行。

# session1:
mysql> begin;
mysql> select * from t1 where c1 = 2 for update;
+------+-------+
| c1   | c2    |
+------+-------+
|    2 | 60530 |
|    2 | 24678 |
+------+-------+
2 rows in set (0.00 sec)
 
# session2:
mysql> select * from t1 where c1 = 2 for update nowait;
ERROR 3572 (HY000): Statement aborted because lock(s) could not be acquired  immediately and NOWAIT is set.
mysql> select * from t1 where c1 = 2 for update skip locked;
Empty set (0.00 sec)

11. 增加SET_VAR語法

在sql語法中增加SET_VAR語法,動態調整部分參數,有利於提升語句性能。

  • select /*+ SET_VAR(sort_buffer_size = 16M) */ id from test order id ;
  • insert /*+ SET_VAR(foreign_key_checks=OFF) */ into test(name) values(1);

12. 支持不可見索引

使用INVISIBLE關鍵字在創建表或者進行表變更中設置索引是否可見。索引不可見只是在查詢時優化器不使用該索引,即使使用force index,優化器也不會使用該索引,同時優化器也不會報索引不存在的錯誤,因爲索引仍然真實存在,在必要時,也可以快速的恢復成可見。

# 創建不可見索引
create table t2(c1 int,c2 int,index idx_c1_c2(c1,c2 desc) invisible );
# 索引可見
alter table t2 alter index idx_c1_c2 visible;
# 索引不可見
alter table t2 alter index idx_c1_c2 invisible;

13. 支持直方圖

優化器會利用column_statistics的數據,判斷字段的值的分佈,得到更準確的執行計劃。

可以使用 ANALYZE TABLE table_name [UPDATE HISTOGRAM on col_name with N BUCKETS |DROP HISTOGRAM ON clo_name] 來收集或者刪除直方圖信息。

直方圖統計了表中某些字段的數據分佈情況,爲優化選擇高效的執行計劃提供參考,直方圖與索引有着本質的區別,維護一個索引有代價。每一次的insert、update、delete都會需要更新索引,會對性能有一定的影響。而直方圖一次創建永不更新,除非明確去更新它。所以不會影響insert、update、delete的性能。

# 添加/更新直方圖
mysql> analyze table t1 update histogram on c1, c2 with 32 buckets;
+--------+-----------+----------+-----------------------------------------------+
| Table  | Op        | Msg_type | Msg_text                                      |
+--------+-----------+----------+-----------------------------------------------+
| db.t1 | histogram | status   | Histogram statistics created for column 'c1'. |
| db.t1 | histogram | status   | Histogram statistics created for column 'c2'. |
+--------+-----------+----------+-----------------------------------------------+
2 rows in set (2.57 sec)
 
# 刪除直方圖
mysql> analyze table t1 drop histogram on c1, c2;
+--------+-----------+----------+-----------------------------------------------+
| Table  | Op        | Msg_type | Msg_text                                      |
+--------+-----------+----------+-----------------------------------------------+
| db.t1 | histogram | status   | Histogram statistics removed for column 'c1'. |
| db.t1 | histogram | status   | Histogram statistics removed for column 'c2'. |
+--------+-----------+----------+-----------------------------------------------+
2 rows in set (0.13 sec)

14. 新增innodb_dedicated_server參數

能夠讓InnoDB根據服務器上檢測到的內存大小自動配置innodb_buffer_pool_size,innodb_log_file_size,innodb_flush_method三個參數。

15. 日誌分類更詳細

在錯誤信息中添加了錯誤信息編號[MY-010311]和錯誤所屬子系統[Server]

# MySQL 5.7
2018-06-08T09:07:20.114585+08:00 0 [Warning] 'proxies_priv' entry '@ root@localhost' ignored in --skip-name-resolve mode.
2018-06-08T09:07:20.117848+08:00 0 [Warning] 'tables_priv' entry 'user mysql.session@localhost' ignored in --skip-name-resolve mode.
2018-06-08T09:07:20.117868+08:00 0 [Warning] 'tables_priv' entry 'sys_config mysql.sys@localhost' ignored in --skip-name-resolve mode.
 
 
# MySQL 8.0
2018-06-21T17:53:13.040295+08:00 28 [Warning] [MY-010311] [Server] 'proxies_priv'  entry '@ root@localhost' ignored in --skip-name-resolve mode.
2018-06-21T17:53:13.040520+08:00 28 [Warning] [MY-010330] [Server] 'tables_priv'  entry 'user mysql.session@localhost' ignored in --skip-name-resolve mode.
2018-06-21T17:53:13.040542+08:00 28 [Warning] [MY-010330] [Server] 'tables_priv'  entry 'sys_config mysql.sys@localhost' ignored in --skip-name-resolve mode.

16. undo空間自動回收

  • innodb_undo_log_truncate參數在8.0.2版本默認值由OFF變爲ON,默認開啓undo日誌表空間自動回收。
  • innodb_undo_tablespaces參數在8.0.2版本默認爲2,當一個undo表空間被回收時,還有另外一個提供正常服務。
  • innodb_max_undo_log_size參數定義了undo表空間回收的最大值,當undo表空間超過這個值,該表空間被標記爲可回收。

17. 增加資源組

MySQL 8.0新增了一個資源組功能,用於調控線程優先級以及綁定CPU核。
MySQL用戶需要有 RESOURCE_GROUP_ADMIN權限才能創建、修改、刪除資源組。
在Linux環境下,MySQL進程需要有 CAP_SYS_NICE 權限才能使用資源組完整功能。

[root@localhost~]# sudo setcap cap_sys_nice+ep /usr/local/mysql8.0/bin/mysqld
[root@localhost~]# getcap /usr/local/mysql8.0/bin/mysqld
/usr/local/mysql8.0/bin/mysqld = cap_sys_nice+ep

默認提供兩個資源組,分別是USR_default,SYS_default

創建資源組:
create resource group test_resouce_group type=USER vcpu=0,1 thread_priority=5;
將當前線程加入資源組:
SET RESOURCE GROUP test_resouce_group;
將某個線程加入資源組:
SET RESOURCE GROUP test_resouce_group FOR thread_id;
查看資源組裏有哪些線程:
select * from Performance_Schema.threads where RESOURCE_GROUP='test_resouce_group';
修改資源組:
alter resource group test_resouce_group vcpu = 2,3 THREAD_PRIORITY = 8;
刪除資源組 :
drop resource group test_resouce_group;

# 創建資源組
mysql>create resource group test_resouce_group type=USER vcpu=0,1 thread_priority=5;
Query OK, 0 rows affected (0.03 sec)

mysql> select * from RESOURCE_GROUPS;
+---------------------+---------------------+------------------------+----------+-----------------+
| RESOURCE_GROUP_NAME | RESOURCE_GROUP_TYPE | RESOURCE_GROUP_ENABLED | VCPU_IDS |  THREAD_PRIORITY |
+---------------------+---------------------+------------------------+----------+-----------------+
| USR_default         | USER                |                      1 | 0-3      |                0 |
| SYS_default         | SYSTEM              |                      1 | 0-3      |                0 |
| test_resouce_group  | USER                |                      1 | 0-1      |                5 |
+---------------------+---------------------+------------------------+----------+-----------------+
3 rows in set (0.00 sec)

# 把線程id爲60的線程加入到資源組test_resouce_group中,線程id可通過Performance_Schema.threads獲取
mysql> SET RESOURCE GROUP test_resouce_group FOR 60;
Query OK, 0 rows affected (0.00 sec)

# 資源組裏有線程時,刪除資源組報錯
mysql> drop resource group test_resouce_group;
ERROR 3656 (HY000): Resource group test_resouce_group is busy.

# 修改資源組
mysql> alter resource group test_resouce_group vcpu = 2,3 THREAD_PRIORITY = 8;
Query OK, 0 rows affected (0.10 sec)
mysql> select * from RESOURCE_GROUPS;
+---------------------+---------------------+------------------------+----------+-----------------+
| RESOURCE_GROUP_NAME | RESOURCE_GROUP_TYPE | RESOURCE_GROUP_ENABLED | VCPU_IDS | THREAD_PRIORITY |
+---------------------+---------------------+------------------------+----------+-----------------+
| USR_default         | USER                |                      1 | 0-3      |               0 |
| SYS_default         | SYSTEM              |                      1 | 0-3      |               0 |
| test_resouce_group  | USER                |                      1 | 2-3      |               8 |
+---------------------+---------------------+------------------------+----------+-----------------+
3 rows in set (0.00 sec)

# 把資源組裏的線程移出到默認資源組USR_default
mysql> SET RESOURCE GROUP USR_default FOR 60;
Query OK, 0 rows affected (0.00 sec)

# 刪除資源組
mysql> drop resource group test_resouce_group;
Query OK, 0 rows affected (0.04 sec)

18. 增加角色管理

角色可以認爲是一些權限的集合,爲用戶賦予統一的角色,權限的修改直接通過角色來進行,無需爲每個用戶單獨授權。

# 創建角色
mysql> create role role_test;
Query OK, 0 rows affected (0.03 sec)
 
# 給角色授予權限
mysql> grant select on db.* to 'role_test';
Query OK, 0 rows affected (0.10 sec)
 
# 創建用戶
mysql> create user 'read_user'@'%' identified by '123456';
Query OK, 0 rows affected (0.09 sec)
 
# 給用戶賦予角色
mysql> grant 'role_test' to 'read_user'@'%';
Query OK, 0 rows affected (0.02 sec)
 
# 給角色role_test增加insert權限
mysql> grant insert on db.* to 'role_test';
Query OK, 0 rows affected (0.08 sec)
 
# 給角色role_test刪除insert權限
mysql> revoke insert on db.* from 'role_test';
Query OK, 0 rows affected (0.10 sec)
 
# 查看默認角色信息
mysql> select * from mysql.default_roles;
+------+-----------+-------------------+-------------------+
| HOST | USER      | DEFAULT_ROLE_HOST | DEFAULT_ROLE_USER |
+------+-----------+-------------------+-------------------+
| %    | read_user | %                 | role_test         |
+------+-----------+-------------------+-------------------+
1 row in set (0.00 sec)
 
# 查看角色與用戶關係
mysql> select * from mysql.role_edges;
+-----------+-----------+---------+-----------+-------------------+
| FROM_HOST | FROM_USER | TO_HOST | TO_USER   | WITH_ADMIN_OPTION |
+-----------+-----------+---------+-----------+-------------------+
| %         | role_test | %       | read_user | N                 |
+-----------+-----------+---------+-----------+-------------------+
1 row in set (0.00 sec)
 
# 刪除角色
mysql> drop role role_test;
Query OK, 0 rows affected (0.06 sec)

 

 

 

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