mysql 表 结构包括那些成员
原以为一个表包括的东西很少的，就只有表的名字，类型，字段的数目，字段的类型，字段的排列，字符集，key的数目，每条字段的数目。。。近来在研究myisam是如何处理blob的时候，看了一下Table.h这个文件的代码，发现，原来一个表是如此复杂的！
由于我对mysql的表了解不深，所以看了代码还是有很多不明白！有没有人推荐一些资料看看，让我知道下面的每一个成员究竟对应什么东西呢？
TABLE_SHARE 结构的代码如下/*
This structure is shared between different table objects. There is one
instance of table share per one table in the database.
*/
typedef struct st_table_share
{
st_table_share() {} /* Remove gcc warning */
/** Category of this table. */
TABLE_CATEGORY table_category;
/* hash of field names (contains pointers to elements of field array) */
HASH name_hash; /* hash of field names */
MEM_ROOT mem_root;
TYPELIB keynames; /* Pointers to keynames */
TYPELIB fieldnames; /* Pointer to fieldnames */
TYPELIB *intervals; /* pointer to interval info */
pthread_mutex_t mutex; /* For locking the share*/
pthread_cond_t cond; /* To signal that share is ready */
struct st_table_share *next, /* Link to unused shares */
**prev;
#ifdef NOT_YET
struct st_table *open_tables; /* link to open tables */
#endif
/* The following is copied to each TABLE on OPEN */
Field **field;
Field **found_next_number_field;
Field *timestamp_field; /* Used only during open */
KEY*key_info; /* data of keys in database */
uint *blob_field; /* Index(下标) to blobs in Field arrray*/
uchar *default_values; /* row with default values */
LEX_STRING comment; /* Comment about table */
CHARSET_INFO *table_charset; /* Default charset of string fields */
MY_BITMAP all_set;
/*
Key which is used for looking-up table in table cache and in the list
of thread's temporary tables. Has the form of:
"database_name\0table_name\0" + optional part for temporary tables.
Note that all three 'table_cache_key', 'db' and 'table_name' members
must be set (and be non-zero) for tables in table cache. They also
should correspond to each other.
To ensure this one can use set_table_cache() methods.
*/
LEX_STRING table_cache_key;
LEX_STRING db; /* Pointer to db */
LEX_STRING table_name; /* Table name (for open) */
LEX_STRING path; /* Path to .frm file (from datadir) */
LEX_STRING normalized_path; /* unpack_filename(path) */
LEX_STRING connect_string;
/*
Set of keys in use, implemented as a Bitmap.
Excludes keys disabled by ALTER TABLE ... DISABLE KEYS.
*/
key_map keys_in_use;
key_map keys_for_keyread;
ha_rows min_rows, max_rows; /* create information */
ulong avg_row_length; /* create information */
ulong raid_chunksize;
ulong version, mysql_version;
ulong timestamp_offset; /* Set to offset+1 of record */
ulong reclength; /* Recordlength 记录长度*/
plugin_ref db_plugin; /* storage engine plugin */
inline handlerton *db_type() const /* table_type for handler */
{
// DBUG_ASSERT(db_plugin);
return db_plugin ? plugin_data(db_plugin, handlerton*) : NULL;
}
enum row_type row_type; /* How rows are stored */
enum ha_storage_media default_storage_media;
char *tablespace;
enum tmp_table_type tmp_table;
enum ha_choice transactional;
uint ref_count; /* How many TABLE objects uses this */
uint open_count; /* Number of tables in open list */
uint blob_ptr_size; /* 4 or 8 */
uint key_block_size; /* create key_block_size, if used */
uint null_bytes, last_null_bit_pos;
uint fields; /* Number of fields */
uint rec_buff_length; /* Size of table->record[] buffer */
uint keys, key_parts;
uint max_key_length, max_unique_length, total_key_length;
uint uniques; /* Number of UNIQUE index */
uint null_fields; /* number of null fields */
uint blob_fields; /* number of blob fields 有多少blob*/
uint timestamp_field_offset; /* Field number for timestamp field */
uint varchar_fields; /* number of varchar fields */
uint db_create_options; /* Create options from database */
uint db_options_in_use; /* Options in use */
uint db_record_offset; /* if HA_REC_IN_SEQ */
uint raid_type, raid_chunks;
uint rowid_field_offset; /* Field_nr +1 to rowid field */
/* Index of auto-updated TIMESTAMP field in field array */
uint primary_key;
uint next_number_index; /* autoincrement key number */
uint next_number_key_offset; /* autoinc keypart offset in a key */
uint next_number_keypart; /* autoinc keypart number in a key */
uint error, open_errno, errarg; /* error from open_table_def() */
uint column_bitmap_size;
uchar frm_version;
bool null_field_first;
bool system; /* Set if system table (one record) */
bool crypted; /* If .frm file is crypted */
bool db_low_byte_first; /* Portable row format */
bool crashed;
bool is_view;
bool name_lock, replace_with_name_lock;
bool waiting_on_cond; /* Protection against free */
ulong table_map_id; /* for row-based replication */
ulonglong table_map_version;
/*
Cache for row-based replication table share checks that does not
need to be repeated. Possible values are: -1 when cache value is
not calculated yet, 0 when table *shall not* be replicated, 1 when
table *may* be replicated.
*/
int cached_row_logging_check;
#ifdef WITH_PARTITION_STORAGE_ENGINE
bool auto_partitioned;
const char *partition_info;
uintpartition_info_len;
uintpartition_info_buffer_size;
const char *part_state;
uint part_state_len;
handlerton *default_part_db_type;
#endif
/*
Set share's table cache key and update its db and table name appropriately.
SYNOPSIS
set_table_cache_key()
key_buff Buffer with already built table cache key to be
referenced from share.
key_lengthKey length.
NOTES
Since 'key_buff' buffer will be referenced from share it should has same
life-time as share itself.
This method automatically ensures that TABLE_SHARE::table_name/db have
appropriate values by using table cache key as their source.
*/
void set_table_cache_key(char *key_buff, uint key_length)
{
table_cache_key.str= key_buff;
table_cache_key.length= key_length;
/*
Let us use the fact that the key is "db/0/table_name/0" + optional
part for temporary tables.
*/
db.str= table_cache_key.str;
db.length= strlen(db.str);
table_name.str= db.str + db.length + 1;
table_name.length= strlen(table_name.str);
}
/*
Set share's table cache key and update its db and table name appropriately.
SYNOPSIS
set_table_cache_key()
key_buff Buffer to be used as storage for table cache key
(should be at least key_length bytes).
key Value for table cache key.
key_lengthKey length.
NOTE
Since 'key_buff' buffer will be used as storage for table cache key
it should has same life-time as share itself.
*/
void set_table_cache_key(char *key_buff, const char *key, uint key_length)
{
memcpy(key_buff, key, key_length);
set_table_cache_key(key_buff, key_length);
}
inline bool honor_global_locks()
{
return ((table_category == TABLE_CATEGORY_USER)
|| (table_category == TABLE_CATEGORY_SYSTEM));
}
inline bool require_write_privileges()
{
return (table_category == TABLE_CATEGORY_PERFORMANCE);
}
} TABLE_SHARE;
查看了一些资料，就知道下面几个成员的意思！其他的还请各位帮忙！
/*
struct st_table *open_tables;
指向打开该表的TABLE结构实例；
ulong reclength;
记录长度；
uint ref_count;
对应的TABLE对象数目；
uint fields;
字段数目；
uint keys；
索引数目；
KEY*key_info;
指向表的索引结构；
uint null_fields;
NULL字段的数目；
uint *blob_field
BLOB字段在Field数组里面的下标
uint blob_fields;
BLOB字段的数目；
uint varchar_fields;
varchar字段的数目；
LEX_STRING table_name;
表名称；
LEX_STRING path；
.frm文件路径（表定义文件）；
*/ 虽然源代码中有一些说明，但是，我还是看不明白！ 看源码的人毕竟是少数吧:lol
继续努力，加油！
有共同研究经历的来讨论吧。
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