数据字典(Data Dictionary)中存储了诸多数据库的元数据信息如图1所示,包括基本Database, table, index, column, function, trigger, procedure,privilege等;以及与存储引擎相关的元数据,如InnoDB的tablespace, table_id, index_id等。MySQL-8.0在数据字典上进行了诸多优化,本文将对其进行逐一介绍。 图1 2. MySQL-8.0...
/*** {* "tableName": "tb_user",* "labCodes": [* "sh",//上海* "gz"//广州* ]* }*/public Boolean createTable(ConfigReq reqObject) {if (CollectionUtils.isEmpty(reqObject.getLabCodes())) {return false;}List<String> labCodes = reqObject.getLabCodes();for (String labCode: labCod...
mysql> alter table sbtest1 add column e int not null default 0; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 1.4-公用表表达式(CTE:Common Table Expression) CTE(Common Table Expression)可以认为是派生表(derived table)的替代,在一定程度上,CTE简化了复杂的join查询和...
# 创建数据库CREATEDATABASEdbtest2;# 使用数据库USEdbtest2;# 创建数据表.隐式的添加索引(在添加有主键约束、唯一性约束或者外键约束的字段会自动的创建索引)CREATETABLEdept(dept_idINTPRIMARYKEYAUTO_INCREMENT,dept_nameVARCHAR(20));CREATETABLEemp(emp_idINTPRIMARYKEYAUTO_INCREMENT,emp_nameVARCHAR(20)UNIQUE,d...
issues found24) Check for invalid table names and schema names used in 5.7No issues found25) Check for orphaned routines in 5.7No issues found26) Check for deprecated usage of single dollar signs in object namesNo issues found27) Check for indexes that are too large to work on higher ...
1.1. MySQL表碎片化(Table Fragmentation)的原因 1.1.1.行碎片(Row fragmentation) 1.1.2. 行间碎片(Intra-row fragmentaion) 1.1.3. 剩余空间碎片(Free space fragmentation) 1.2. MySQL中如何找出碎片化严重的表 1.2.1. 方法1:使用show table status from xxxx like 'xxxx' \G; ...
27) Check for indexes that are too large to work on higher versions of MySQL Server than 5.7 No issues found 28) Check for deprecated '.<table>' syntax used in routines. No issues found Errors: 0 Warnings: 3 Notices: 1 NOTE: No fatal errors were found that would prevent an upgrade,...
笔者设置table_cache = 256 优化key_buffer_sizekey_buffer_size指定索引缓冲区的大小,它决定索引处理的速度, 尤其是索引读的速度。通过检查状态值Key_read_requests和Key_reads,可以知道key_buffer_size设置是否合理。 比例key_reads / key_read_requests应该尽可能的低,至少是1:100,1:1000更好 ...
mysql5 默认加密方式是 my_native_password mysql8 默认加密方式是 caching_sha2_password 这个问题就是使用了caching_sha2_password加密方式却找不到某个必需的文件 先进入mysql, 然后修改mysql默认的加密方式为mysql_native_password 也就是下面两行命令: ...
table_cache – 512 open_tables – 103 opened_tables – 1273 uptime – 4021421 (measured in seconds) 1. 2. 3. 4. 该案例中table_cache似乎设置得太高了。在峰值时间,打开表的数目比table_cache要少得多。 案例2:该案例来自一台开发服务器。