discard表空间之后

原创黄超 2022-05-18

2383

某DBA说某个mysql不断重启，请求紧急救援。MySQL 版本5.7.28-log MySQL Community Server

一、诊断

1.查看错误日志

2022-03-09T12:45:27.011345+08:00 5 [Warning] InnoDB: Tablespace for table `hc`.`student` is set as discarded.
2022-03-09T12:45:27.011433+08:00 5 [Warning] InnoDB: Cannot calculate statistics for table `hc`.`student` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2022-03-09 12:45:27 0x7fd8a1f96700  InnoDB: Assertion failure in thread 140568407140096 in file ha_innodb.cc line 21060
InnoDB: Failing assertion: format != 0
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
04:45:27 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
Attempting to collect some information that could help diagnose the problem.
As this is a crash and something is definitely wrong, the information
collection process might fail.

key_buffer_size=33554432
read_buffer_size=131072
max_used_connections=1
max_threads=3000
thread_count=4
connection_count=1
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 49608916 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.


复制

2.查看系统表信息

mysql>SELECT * FROM information_schema.`INNODB_SYS_TABLES` where name like '%student%';
+----------+------------------+------+--------+-------+-------------+------------+---------------+------------+
| TABLE_ID | NAME             | FLAG | N_COLS | SPACE | FILE_FORMAT | ROW_FORMAT | ZIP_PAGE_SIZE | SPACE_TYPE |
+----------+------------------+------+--------+-------+-------------+------------+---------------+------------+
|       77 | hc/student#P#p01 |   33 |      7 |    44 | Barracuda   | Dynamic    |             0 | Single     |
|       78 | hc/student#P#p02 |   33 |      7 |    45 | Barracuda   | Dynamic    |             0 | Single     |
|       79 | hc/student#P#p03 |   33 |      7 |    46 | Barracuda   | Dynamic    |             0 | Single     |
|       80 | hc/student#P#p04 |   33 |      7 |    47 | Barracuda   | Dynamic    |             0 | Single     |
|       81 | hc/student#P#p05 |   33 |      7 |    48 | Barracuda   | Dynamic    |             0 | Single     |
|       82 | hc/student#P#p06 |   33 |      7 |    49 | Barracuda   | Dynamic    |             0 | Single     |
|       83 | hc/student#P#p07 |   33 |      7 |    50 | Barracuda   | Dynamic    |             0 | Single     |
|       84 | hc/student#P#p08 |   33 |      7 |    51 | Barracuda   | Dynamic    |             0 | Single     |
|       85 | hc/student#P#p09 |   33 |      7 |    52 | Barracuda   | Dynamic    |             0 | Single     |
|       86 | hc/student#P#p10 |   33 |      7 |    53 | Barracuda   | Dynamic    |             0 | Single     |
+----------+------------------+------+--------+-------+-------------+------------+---------------+------------+

复制

3.查看表空间文件

#ll  hc/student#P*
ls: cannot access student#P*: No such file or directory

复制

二、分析

询问了某DBA，他说磁盘不足，为了回收空间，给一个大表做了discard表空间(alter table hc.student discard tablespace;)，保留表结构。
这是一个错误操作！想回收表空间又想保留表结构的，应该给表执行truncate。
目前MySQL系统数据字典里面还存有这个表的结构，磁盘还剩下frm文件，缺少ibd文件，可以直接drop表，再新create 表。

三、解决

1.删除表

mysql>drop table hc.student;
Query OK, 0 rows affected (0.00 sec)
mysql>SELECT * FROM information_schema.`INNODB_SYS_TABLES` where name like '%mytable%'; 
Empty set (0.00 sec)

复制

2.查看错误日志

2022-03-09T13:29:52.514287+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student /* p01 /.
2022-03-09T13:29:52.518869+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p02 /.
2022-03-09T13:29:52.522095+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p03 /.
2022-03-09T13:29:52.525972+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p04 /.
2022-03-09T13:29:52.527964+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p05 /.
2022-03-09T13:29:52.530321+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p06 /.
2022-03-09T13:29:52.533096+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p07 /.
2022-03-09T13:29:52.534936+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p08 /.
2022-03-09T13:29:52.538642+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p09 /.
2022-03-09T13:29:52.541594+08:00 5 [Warning] InnoDB: Missing .ibd file for table hc.student / p10 */.

3.恢复表结构

mysql>create table hc.student

复制

四、概念知识

MySQL在设置innodb_file_per_table=on后，每个innodb表拥有独立表空间，每个新增加的innodb表会生成两个文件
table_name.frm -------表结构文件
table_name.ibd -------表空间文件

表空间操作
alter table table_name discard tablespace; ------卸载表空间，会删除ibd文件
alter table table_name import tablespace; ------加载表空间

误删frm文件或ibd文件救援

1.frm文件被误删除

mysql> select * from student;
ERROR 1146 (42S02): Table 'db1.student' doesn't exist
mysql> SELECT * FROM information_schema.`INNODB_SYS_TABLES` where name like '%student%';
+----------+-------------+------+--------+-------+-------------+------------+---------------+------------+
| TABLE_ID | NAME        | FLAG | N_COLS | SPACE | FILE_FORMAT | ROW_FORMAT | ZIP_PAGE_SIZE | SPACE_TYPE |
+----------+-------------+------+--------+-------+-------------+------------+---------------+------------+
|       62 | db1/student |   33 |      5 |    38 | Barracuda   | Dynamic    |             0 | Single     |
+----------+-------------+------+--------+-------+-------------+------------+---------------+------------+
1 row in set (0.00 sec)
mysql> drop table student;
ERROR 1051 (42S02): Unknown table 'db1.student'
mysql> create table student(id int,name varchar(30));
ERROR 1030 (HY000): Got error 168 from storage engine

复制

解决：
1.1 ibd文件先备份。
1.2 从其他库新增同名表create table。
1.3 cp 新frm过来
1.4 chown 修改属组

2.ibd文件被误删除

mysql>select * from student;
ERROR 1812 (HY000): Tablespace is missing for table `db1`.`student`.
mysql> optimize table student;
+-------------+----------+----------+-------------------------------------------------------------------+
| Table       | Op       | Msg_type | Msg_text                                                          |
+-------------+----------+----------+-------------------------------------------------------------------+
| db1.student | optimize | note     | Table does not support optimize, doing recreate + analyze instead |
| db1.student | optimize | error    | Got error 44 from storage engine                                  |
| db1.student | optimize | status   | Operation failed                                                  |
+-------------+----------+----------+-------------------------------------------------------------------+
复制

解决：
2.1 若是表不需要了，可以直接drop table
2.2 若是表需要，数据需要，把备份的ibd文件拷贝回来，select查询是否成功，否则加载表空间import tablespace，最后利用mysqlbinlog 处理增量数据。
2.3 若是表需要，数据不需要了，先drop table，再ceate table