一、为什么会产生碎片
简单的说,删除数据必然会在数据文件中造成不连续的空白空间,而当插入数据时,这些空白空间则会被利用起来.于是造成了数据的存储位置不连续,以及物理存储顺序与理论上的排序顺序不同,这种是数据碎片.实际上数据碎片分为两种,一种是单行数据碎片,另一种是多行数据碎片.前者的意思就是一行数据,被分成N个片段,存储在N个位置.后者的就是多行数据并未按照逻辑上的顺序排列.当有大量的删除和插入操作时,必然会产生很多未使用的空白空间,这些空间就是多出来的额外空间.索引也是文件数据,所以也会产生索引碎片,理由同上,大概就是顺序紊乱的问题.Engine 不同,OPTIMIZE 的操作也不一样的,MyISAM 因为索引和数据是分开的,所以 OPTIMIZE 可以整理数据文件,并重排索引。这样不但会浪费空间，并且查询速度也更慢。
二、Innodb 表碎片整理
1、查看表行数
1）行数
MariaDB [agent_platform]> select count(1) from corporationprofit_old;
+----------+
| count(1) |
+----------+
| 18198196 |
+----------+
1 row in set (54.35 sec)
2）所占磁盘大小
9218180KB
cat test.sh
a=`ls /u02/mysql/data/agent_platform/corporationprofit_old*|xargs du|awk '{print $1}'`
m=0
for i in $a
do
echo $i
((m=$m+$i))
done
echo $m
3）查看表的信息
MariaDB [(none)]> select ROW_FORMAT,TABLE_ROWS,DATA_LENGTH,INDEX_LENGTH,MAX_DATA_LENGTH,DATA_FREE,ENGINE
-> from information_schema.TABLES where TABLE_SCHEMA='agent_platform' and TABLE_NAME='corporationprofit_old' limit 1;
+------------+------------+-------------+--------------+-----------------+------------+--------+
| ROW_FORMAT | TABLE_ROWS | DATA_LENGTH | INDEX_LENGTH | MAX_DATA_LENGTH | DATA_FREE | ENGINE |
+------------+------------+-------------+--------------+-----------------+------------+--------+
| Compact | 17105657 | 5187551232 | 2068905984 | 0 | 1101004800 | InnoDB |
+------------+------------+-------------+--------------+-----------------+------------+--------+
1 row in set (0.25 sec)
2、删除部分数据
1）总共删除了8157318行
MariaDB [agent_platform]> delete from corporationprofit_old where date_created>='2018-10-01' ;
Query OK, 8157318 rows affected (2 min 52.18 sec)
2）查看表的行数
MariaDB [agent_platform]> select count(1) from corporationprofit_old;
+----------+
| count(1) |
+----------+
| 10040878 |
+----------+
1 row in set (11.66 sec)
3）查看表的信息
MariaDB [agent_platform]> select ROW_FORMAT,TABLE_ROWS,DATA_LENGTH,INDEX_LENGTH,MAX_DATA_LENGTH,DATA_FREE,ENGINE
-> from information_schema.TABLES where TABLE_SCHEMA='agent_platform' and TABLE_NAME='corporationprofit_old' limit 1;
+------------+------------+-------------+--------------+-----------------+------------+--------+
| ROW_FORMAT | TABLE_ROWS | DATA_LENGTH | INDEX_LENGTH | MAX_DATA_LENGTH | DATA_FREE | ENGINE |
+------------+------------+-------------+--------------+-----------------+------------+--------+
| Compact | 9779701 | 5360599040 | 2138177536 | 0 | 4380950528 | InnoDB |
+------------+------------+-------------+--------------+-----------------+------------+--------+
1 row in set (0.30 sec)
4）查看表删除后所占磁盘大小
9218180KB，没有改变
3、表数据碎片整理
1）表数据整理
MariaDB [agent_platform]> OPTIMIZE table corporationprofit_old;
+--------------------------------------+----------+----------+-------------------------------------------------------------------+
| Table | Op | Msg_type | Msg_text |
+--------------------------------------+----------+----------+-------------------------------------------------------------------+
| agent_platform.corporationprofit_old | optimize | note | Table does not support optimize, doing recreate + analyze instead |
| agent_platform.corporationprofit_old | optimize | status | OK |
+--------------------------------------+----------+----------+-------------------------------------------------------------------+
2 rows in set (5 min 34.79 sec)
2）查看表信息
MariaDB [agent_platform]> select ROW_FORMAT,TABLE_ROWS,DATA_LENGTH,INDEX_LENGTH,MAX_DATA_LENGTH,DATA_FREE,ENGINE
-> from information_schema.TABLES where TABLE_SCHEMA='agent_platform' and TABLE_NAME='corporationprofit_old' limit 1;
+------------+------------+-------------+--------------+-----------------+-----------+--------+
| ROW_FORMAT | TABLE_ROWS | DATA_LENGTH | INDEX_LENGTH | MAX_DATA_LENGTH | DATA_FREE | ENGINE |
+------------+------------+-------------+--------------+-----------------+-----------+--------+
| Compact | 9863806 | 2996649984 | 854638592 | 0 | 6291456 | InnoDB |
+------------+------------+-------------+--------------+-----------------+-----------+--------+
3）产看整理后所占磁盘大小
3881468KB
碎片整理后，表的大小比之前减少了5GB。