MySQL源码之--Table_cache

一.table_cache 相关参数

1.open_files_limit
2.max_connections
3.table_open_cache
4.table_definition_cache

问题？

经常会看到自己my.cnf设置的那四个值和在MySQL中看到的值不一样.

我修改了其中一个参数，结构发现所有的上面的四个参数都发生了变化。
参数到底应该设置为多少合适？

二.源码分析之初始化

1.常量定义

源码位置:/sql/sql_const.h

#define TABLE_OPEN_CACHE_MIN    400
#define TABLE_OPEN_CACHE_DEFAULT 2000
#define TABLE_DEF_CACHE_DEFAULT 400
#define MAX_CONNECTIONS_DEFAULT 151
#define TABLE_DEF_CACHE_MIN     400

源码位置:/mysql-5.7.33/my_global.h

#ifdef _WIN32
#define MY_FILE_MIN  2048
#else
#define MY_FILE_MIN  0
#endif

#ifdef _WIN32
#define MY_NFILE (16384 + MY_FILE_MIN)
#else
#define MY_NFILE 64
#endif

#define OS_FILE_LIMIT	UINT_MAX

2.变量静态文件

源码位置:/mysql-5.7.33/sql/sys_vars.cc

static Sys_var_ulong Sys_open_files_limit(
       "open_files_limit",
       "If this is not 0, then mysqld will use this value to reserve file "
       "descriptors to use with setrlimit(). If this value is 0 then mysqld "
       "will reserve max_connections*5 or max_connections + table_open_cache*2 "
       "(whichever is larger) number of file descriptors",
       READ_ONLY GLOBAL_VAR(open_files_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, OS_FILE_LIMIT), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL), ON_UPDATE(NULL),
       NULL,
       sys_var::PARSE_EARLY);

static Sys_var_ulong Sys_max_connections(
       "max_connections", "The number of simultaneous clients allowed",
       GLOBAL_VAR(max_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 100000),
       DEFAULT(MAX_CONNECTIONS_DEFAULT),
       BLOCK_SIZE(1),
       NO_MUTEX_GUARD,
       NOT_IN_BINLOG,
       ON_CHECK(0),
       ON_UPDATE(0),
       NULL,
       sys_var::PARSE_EARLY);


static bool fix_table_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
   
  table_cache_size_per_instance= table_cache_size / table_cache_instances;
  return false;
}

static Sys_var_ulong Sys_table_cache_size(
       "table_open_cache&