淺談為什么MySQL不建議delete刪除數(shù)據(jù)

CREATE TABLESPACE tablespace_name
  ADD DATAFILE 'file_name'        #數(shù)據(jù)文件名
  USE LOGFILE GROUP logfile_group    #自定義日志文件組，一般每組2個(gè)logfile。
  [EXTENT_SIZE [=] extent_size]     #區(qū)大小
  [INITIAL_SIZE [=] initial_size]    #初始化大小 
  [AUTOEXTEND_SIZE [=] autoextend_size] #自動(dòng)擴(kuò)寬尺寸
  [MAX_SIZE [=] max_size]        #單個(gè)文件最大size，最大是32G。
  [NODEGROUP [=] nodegroup_id]      #節(jié)點(diǎn)組
  [WAIT]
  [COMMENT [=] comment_text]
  ENGINE [=] engine_name

#創(chuàng)建熱數(shù)據(jù)表空間
create tablespace tbs_data_hot add datafile '/hot_data/tbs_data_hot01.dbf' max_size 20G;
#創(chuàng)建核心業(yè)務(wù)表存儲(chǔ)在熱數(shù)據(jù)表空間
create table booking(id bigint not null primary key auto_increment, …… ) tablespace tbs_data_hot;
#創(chuàng)建冷數(shù)據(jù)表空間
create tablespace tbs_data_cold add datafile '/hot_data/tbs_data_cold01.dbf' max_size 20G;
#創(chuàng)建日志，流水，備份類的表存儲(chǔ)在冷數(shù)據(jù)表空間
create table payment_log(id bigint not null primary key auto_increment, …… ) tablespace tbs_data_cold;
#可以移動(dòng)表到另一個(gè)表空間
alter table payment_log tablespace tbs_data_hot;

mysql> create table user(id bigint not null primary key auto_increment, 
  -> name varchar(20) not null default '' comment '姓名', 
  -> age tinyint not null default 0 comment 'age', 
  -> gender char(1) not null default 'M' comment '性別',
  -> phone varchar(16) not null default '' comment '手機(jī)號(hào)',
  -> create_time datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '創(chuàng)建時(shí)間',
  -> update_time datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改時(shí)間'
  -> ) engine = InnoDB DEFAULT CHARSET=utf8mb4 COMMENT '用戶信息表';
Query OK, 0 rows affected (0.26 sec)

# ls -lh user1.ibd 
-rw-r----- 1 mysql mysql 96K Nov 6 12:48 user.ibd

# python2 py_innodb_page_info.py -v /data2/mysql/test/user.ibd
page offset 00000000, page type File Space Header>
page offset 00000001, page type Insert Buffer Bitmap>
page offset 00000002, page type File Segment inode>
page offset 00000003, page type B-tree Node>, page level 0000>
page offset 00000000, page type Freshly Allocated Page>
page offset 00000000, page type Freshly Allocated Page>
Total number of page: 6:   #總共分配的頁數(shù)
Freshly Allocated Page: 2   #可用的數(shù)據(jù)頁
Insert Buffer Bitmap: 1    #插入緩沖頁
File Space Header: 1     #文件空間頭
B-tree Node: 1        #數(shù)據(jù)頁
File Segment inode: 1     #文件端inonde，如果是在ibdata1.ibd上會(huì)有多個(gè)inode。

mysql> DELIMITER $$
mysql> CREATE PROCEDURE insert_user_data(num INTEGER) 
  -> BEGIN
  ->   DECLARE v_i int unsigned DEFAULT 0;
  -> set autocommit= 0;
  -> WHILE v_i  num DO
  ->  insert into user(`name`, age, gender, phone) values (CONCAT('lyn',v_i), mod(v_i,120), 'M', CONCAT('152',ROUND(RAND(1)*100000000)));
  -> SET v_i = v_i+1;
  -> END WHILE;
  -> commit;
  -> END $$
Query OK, 0 rows affected (0.01 sec)
mysql> DELIMITER ;

#插入10w數(shù)據(jù)
mysql> call insert_user_data(100000);
Query OK, 0 rows affected (6.69 sec)

# ls -lh user.ibd
-rw-r----- 1 mysql mysql 14M Nov 6 10:58 /data2/mysql/test/user.ibd

# python2 py_innodb_page_info.py -v /data2/mysql/test/user.ibd
page offset 00000000, page type File Space Header>
page offset 00000001, page type Insert Buffer Bitmap>
page offset 00000002, page type File Segment inode>
page offset 00000003, page type B-tree Node>, page level 0001>  #增加了一個(gè)非葉子節(jié)點(diǎn)，樹的高度從1變?yōu)?.
........................................................
page offset 00000000, page type Freshly Allocated Page>
Total number of page: 896:
Freshly Allocated Page: 493
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 400
File Segment inode: 1

mysql> select min(id),max(id),count(*) from user;
+---------+---------+----------+
| min(id) | max(id) | count(*) |
+---------+---------+----------+
|    1 | 100000 |  100000 |
+---------+---------+----------+
1 row in set (0.05 sec)
#刪除50000條數(shù)據(jù)，理論上空間應(yīng)該從14MB變長(zhǎng)7MB左右。
mysql> delete from user limit 50000;
Query OK, 50000 rows affected (0.25 sec)

 
#數(shù)據(jù)文件大小依然是14MB，沒有縮小。
# ls -lh /data2/mysql/test/user1.ibd 
-rw-r----- 1 mysql mysql 14M Nov 6 13:22 /data2/mysql/test/user.ibd

#數(shù)據(jù)頁沒有被回收。
# python2 py_innodb_page_info.py -v /data2/mysql/test/user.ibd
page offset 00000000, page type File Space Header>
page offset 00000001, page type Insert Buffer Bitmap>
page offset 00000002, page type File Segment inode>
page offset 00000003, page type B-tree Node>, page level 0001>
........................................................
page offset 00000000, page type Freshly Allocated Page>
Total number of page: 896:
Freshly Allocated Page: 493
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 400
File Segment inode: 1
#在MySQL內(nèi)部是標(biāo)記刪除，

mysql> use information_schema;

Database changed
mysql> SELECT A.SPACE AS TBL_SPACEID, A.TABLE_ID, A.NAME AS TABLE_NAME, FILE_FORMAT, ROW_FORMAT, SPACE_TYPE, B.INDEX_ID , B.NAME AS INDEX_NAME, PAGE_NO, B.TYPE AS INDEX_TYPE FROM INNODB_SYS_TABLES A LEFT JOIN INNODB_SYS_INDEXES B ON A.TABLE_ID =B.TABLE_ID WHERE A.NAME = 'test/user1';
+-------------+----------+------------+-------------+------------+------------+----------+------------+---------+------------+
| TBL_SPACEID | TABLE_ID | TABLE_NAME | FILE_FORMAT | ROW_FORMAT | SPACE_TYPE | INDEX_ID | INDEX_NAME | PAGE_NO | INDEX_TYPE |
+-------------+----------+------------+-------------+------------+------------+----------+------------+---------+------------+
|    1283 |   1207 | test/user | Barracuda  | Dynamic  | Single   |   2236 | PRIMARY  |    3 |     3 |
+-------------+----------+------------+-------------+------------+------------+----------+------------+---------+------------+
1 row in set (0.01 sec)

PAGE_NO = 3 標(biāo)識(shí)B-tree的root page是3號(hào)頁，INDEX_TYPE = 3是聚集索引。 INDEX_TYPE取值如下：
0 = nonunique secondary index; 
1 = automatically generated clustered index (GEN_CLUST_INDEX); 
2 = unique nonclustered index; 
3 = clustered index; 
32 = full-text index;
#收縮空間再后進(jìn)行觀察

mysql> select table_schema,
  ->    table_name,ENGINE,
  ->    round(DATA_LENGTH/1024/1024+ INDEX_LENGTH/1024/1024) total_mb,TABLE_ROWS,
  ->    round(DATA_LENGTH/1024/1024) data_mb, round(INDEX_LENGTH/1024/1024) index_mb, round(DATA_FREE/1024/1024) free_mb, round(DATA_FREE/DATA_LENGTH*100,2) free_ratio
  -> from information_schema.TABLES where TABLE_SCHEMA= 'test'
  -> and TABLE_NAME= 'user';
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
| table_schema | table_name | ENGINE | total_mb | TABLE_ROWS | data_mb | index_mb | free_mb | free_ratio |
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
| test     | user   | InnoDB |    4 |   50000 |    4 |    0 |    6 |   149.42 |
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
1 row in set (0.00 sec)

#執(zhí)行InnoDB的碎片回收
mysql> alter table user engine=InnoDB;
Query OK, 0 rows affected (9.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

##執(zhí)行完之后，數(shù)據(jù)文件大小從14MB降低到10M。
# ls -lh /data2/mysql/test/user1.ibd 
-rw-r----- 1 mysql mysql 10M Nov 6 16:18 /data2/mysql/test/user.ibd

mysql> select table_schema,    table_name,ENGINE,    round(DATA_LENGTH/1024/1024+ INDEX_LENGTH/1024/1024) total_mb,TABLE_ROWS,    round(DATA_LENGTH/1024/1024) data_mb, round(INDEX_LENGTH/1024/1024) index_mb, round(DATA_FREE/1024/1024) free_mb, round(DATA_FREE/DATA_LENGTH*100,2) free_ratio from information_schema.TABLES where TABLE_SCHEMA= 'test' and TABLE_NAME= 'user';
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
| table_schema | table_name | ENGINE | total_mb | TABLE_ROWS | data_mb | index_mb | free_mb | free_ratio |
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
| test     | user   | InnoDB |    5 |   50000 |    5 |    0 |    2 |   44.29 |
+--------------+------------+--------+----------+------------+---------+----------+---------+------------+
1 row in set (0.00 sec)

#插入100W數(shù)據(jù)
mysql> call insert_user_data(1000000);
Query OK, 0 rows affected (35.99 sec)

#添加相關(guān)索引
mysql> alter table user add index idx_name(name), add index idx_phone(phone);
Query OK, 0 rows affected (6.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

#表上索引統(tǒng)計(jì)信息
mysql> show index from user;
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| user |     0 | PRIMARY  |      1 | id     | A     |   996757 |   NULL | NULL  |   | BTREE   |     |        |
| user |     1 | idx_name |      1 | name    | A     |   996757 |   NULL | NULL  |   | BTREE   |     |        |
| user |     1 | idx_phone |      1 | phone    | A     |      2 |   NULL | NULL  |   | BTREE   |     |        |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)

#重置狀態(tài)變量計(jì)數(shù)
mysql> flush status;
Query OK, 0 rows affected (0.00 sec)

#執(zhí)行SQL語句
mysql> select id, age ,phone from user where name like 'lyn12%';
+--------+-----+-------------+
| id   | age | phone    |
+--------+-----+-------------+
|  124 |  3 | 15240540354 |
|  1231 | 30 | 15240540354 |
| 12301 | 60 | 15240540354 |
.............................
| 129998 | 37 | 15240540354 |
| 129999 | 38 | 15240540354 |
| 130000 | 39 | 15240540354 |
+--------+-----+-------------+
11111 rows in set (0.03 sec)

mysql> explain select id, age ,phone from user where name like 'lyn12%';
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
| id | select_type | table | type | possible_keys | key   | key_len | ref | rows | Extra         |
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
| 1 | SIMPLE   | user | range | idx_name   | idx_name | 82   | NULL | 22226 | Using index condition |
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
1 row in set (0.00 sec)

#查看相關(guān)狀態(tài)呢變量
mysql> select * from information_schema.session_status where variable_name in('Last_query_cost','Handler_read_next','Innodb_pages_read','Innodb_data_reads','Innodb_pages_read');
+-------------------+----------------+
| VARIABLE_NAME   | VARIABLE_VALUE |
+-------------------+----------------+
| HANDLER_READ_NEXT | 11111     |  #請(qǐng)求讀的行數(shù)
| INNODB_DATA_READS | 7868409    |  #數(shù)據(jù)物理讀的總數(shù)
| INNODB_PAGES_READ | 7855239    |  #邏輯讀的總數(shù)
| LAST_QUERY_COST  | 10.499000   |  #SQL語句的成本COST，主要包括IO_COST和CPU_COST。
+-------------------+----------------+
4 rows in set (0.00 sec)

#刪除50w數(shù)據(jù)
mysql> delete from user limit 500000;
Query OK, 500000 rows affected (3.70 sec)

#分析表統(tǒng)計(jì)信息
mysql> analyze table user;
+-----------+---------+----------+----------+
| Table   | Op   | Msg_type | Msg_text |
+-----------+---------+----------+----------+
| test.user | analyze | status  | OK    |
+-----------+---------+----------+----------+
1 row in set (0.01 sec)

#重置狀態(tài)變量計(jì)數(shù)
mysql> flush status;
Query OK, 0 rows affected (0.01 sec)

mysql> select id, age ,phone from user where name like 'lyn12%';
Empty set (0.05 sec)

mysql> explain select id, age ,phone from user where name like 'lyn12%';
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
| id | select_type | table | type | possible_keys | key   | key_len | ref | rows | Extra         |
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
| 1 | SIMPLE   | user | range | idx_name   | idx_name | 82   | NULL | 22226 | Using index condition |
+----+-------------+-------+-------+---------------+----------+---------+------+-------+-----------------------+
1 row in set (0.00 sec)

mysql> select * from information_schema.session_status where variable_name in('Last_query_cost','Handler_read_next','Innodb_pages_read','Innodb_data_reads','Innodb_pages_read');
+-------------------+----------------+
| VARIABLE_NAME   | VARIABLE_VALUE |
+-------------------+----------------+
| HANDLER_READ_NEXT | 0       |
| INNODB_DATA_READS | 7868409    |
| INNODB_PAGES_READ | 7855239    |
| LAST_QUERY_COST  | 10.499000   |
+-------------------+----------------+
4 rows in set (0.00 sec)