MySQL另类的备份恢复方法——innodb可传输表空间

 

Preface

 

    There're many ways in backing up or migrating data from one server to another one.Logically,we can use mysqldump,mydumper,mypump to do that kind of job.Physically,we can use Xtrabackup even cold copy way.What I'm gonna introduce is a special method to transmit data between MySQL servers which called “transportable tablespace”.

 

Introduction

 

    What's transportable tablespace?It is supported only on innodb engine and based on export/import grammer of "alter table ... ;" clause since MySQL 5.6.6 version.As we all know,innodb supports putting data of tables in their own tablespaces instead of shared system tablespace by setting parameter "innodb_file_per_table=1".It's different from the conception of oracle database.Business tables in oracle can be stored togerther with each other in the same tablespace while MySQL oblying the rule of "one table one ibd".That is,these ".ibd" files is what we really need to transport.

 

Scenarios

• Transport a single table to report server without influencing loads on product.
• Transport a single table to slave server for correcting the replication errors about the table.
• Transport a single table to better storages such as ssd device for special purpose.
• Restore a big table efficiently and swiftly as mysqldump needs to reinsert data and rebuild indexes.

 

Limitations

• "innodb_file_per_table" should be set to "on"(the same to slave server if in replication structure).
• Page size on instance of target server should be same as the one on source server.
• It doesn't support partition table and tables which contains fulltext indexes.
• "foreign_key_checks" should be set to "0" if there's a paraent-child relationship in a table.
• It doesn't check the foreign key constraints when importing,so all relevant tables should be exported at the same time.
• Target instance must has the same version of series with the source instance.
• it's recommended to set "lower_case_table" to "1" to avoid import problems.

Example

 

Check the table which you want to transport first(eg. ”sbtest2” in database "sysbench" here).

 (root@localhost mysql3306.sock)[sysbench]>show tables;
 +--------------------+
 | Tables_in_sysbench |
 +--------------------+
 | sbtest1            |
 | sbtest10           |
 | sbtest2            |
 | sbtest3            |
 | sbtest4            |
 | sbtest5            |
 | sbtest6            |
 | sbtest7            |
 | sbtest8            |
 | sbtest9            |
 +--------------------+
  rows in set (0.00 sec)
 
 (root@localhost mysql3306.sock)[sysbench]>show create table sbtest2\G
 *************************** . row ***************************
        Table: sbtest2
 Create Table: CREATE TABLE `sbtest2` (
   `id` int() NOT NULL AUTO_INCREMENT,
   `k` int() NOT NULL DEFAULT '',
   `c` char() NOT NULL DEFAULT '',
   `pad` char() NOT NULL DEFAULT '',
   PRIMARY KEY (`id`),
   KEY `k_2` (`k`)
 ) ENGINE=InnoDB AUTO_INCREMENT= DEFAULT CHARSET=utf8
  row in set (0.00 sec)
 
 (root@localhost mysql3306.sock)[sysbench]>select count(*) from sbtest2;
 +----------+
 | count(*) |
 +----------+
 |    |
 +----------+
  row in set (0.07 sec)
 
 (root@localhost mysql3306.sock)[sysbench]>show variables like '%innodb_file_per_table%';
 +-----------------------+-------+
 | Variable_name         | Value |
 +-----------------------+-------+
 | innodb_file_per_table | ON    |
 +-----------------------+-------+
  row in set (0.00 sec)

Create the structure of table sbtest2 in database "tt” of target instance.

 (root@localhost mysql3306.sock)[tt]>CREATE TABLE `sbtest2` (
     ->   `id` int() NOT NULL AUTO_INCREMENT,
     ->   `k` int() NOT NULL DEFAULT '',
     ->   `c` char() NOT NULL DEFAULT '',
     ->   `pad` char() NOT NULL DEFAULT '',
     ->   PRIMARY KEY (`id`),
     ->   KEY `k_2` (`k`)
     -> ) ENGINE=InnoDB AUTO_INCREMENT= DEFAULT CHARSET=utf8;
 Query OK,  rows affected (0.02 sec)
 
 (root@localhost mysql3306.sock)[tt]>select count(*) from sbtest2;
 +----------+
 | count(*) |
 +----------+
 |         |
 +----------+
  row in set (0.00 sec)
 
 (root@localhost mysql3306.sock)[tt]>show variables like '%innodb_file_per_table%';
 +-----------------------+-------+
 | Variable_name         | Value |
 +-----------------------+-------+
 | innodb_file_per_table | ON    |
 +-----------------------+-------+
  row in set (0.00 sec)

Detach the tablespace of table "sbtest2"  on target.

 (root@localhost mysql3306.sock)[zlm]>alter table sbtest2 discard tablespace;
 Query OK,  rows affected (0.00 sec)
 
 [root@zlm3 :: /data/mysql/mysql3306/data/tt]
 #ls -l
 total
 -rw-r-----  mysql mysql    Jul   : db.opt
 -rw-r-----  mysql mysql  Jul   : sbtest2.frm //The sbtest2.ibd file has been deleted.

Flush the "sbtest2" table on source.

 (root@localhost mysql3306.sock)[sysbench]>flush table sbtest2 for export;
 Query OK,  rows affected (0.00 sec)
 
 [root@zlm2 :: /data/mysql/mysql3306/data/sysbench]
 #ls -l|grep sbtest2
 -rw-r-----  mysql mysql       Jul   : sbtest2.cfg
 -rw-r-----  mysql mysql      Jul   : sbtest2.frm
 -rw-r-----  mysql mysql  Jul   : sbtest2.ibd //A .cfg file has been created now.
 
 --05T08::.515902Z  [Note] InnoDB: Sync to disk of `sysbench`.`sbtest2` started.
 --05T08::.515929Z  [Note] InnoDB: Stopping purge
 --05T08::.516147Z  [Note] InnoDB: Writing table metadata to './sysbench/sbtest2.cfg'
 --05T08::.516276Z  [Note] InnoDB: Table `sysbench`.`sbtest2` flushed to disk
 
 //error log shows the information after flush operation.
 //table metadata has been written into the .cfg file.

Copy .ibd & .cfg file to target.

 [root@zlm2 :: /data/mysql/mysql3306/data/sysbench]
 #scp sbtest2.{ibd,cfg} zlm3:/data/mysql/mysql3306/data/tt/
 root@zlm3's password:
 sbtest2.ibd                                                                                                        %   29MB  .0MB/s   :
 sbtest2.cfg                                                                                                        %       .6KB/s   :

Release the lock resources on source instance.

 (root@localhost mysql3306.sock)[sysbench]>unlock tables;
 Query OK,  rows affected (0.00 sec)
 
 [root@zlm2 :: /data/mysql/mysql3306/data/sysbench]
 #ls -l|grep sbtest2
 -rw-r-----  mysql mysql      Jul   : sbtest2.frm
 -rw-r-----  mysql mysql  Jul   : sbtest2.ibd
 
 --05T08::.256442Z  [Note] InnoDB: Deleting the meta-data file './sysbench/sbtest2.cfg'
 --05T08::.256458Z  [Note] InnoDB: Resuming purge
 
 //The .cfg file will be deleted after execute "unlock tables;"

Check the files "sbtest2" table needs and give it the mysql privileges.

 [root@zlm3 :: /data/mysql/mysql3306/data/tt]
 #ls -l
 total
 -rw-r-----  mysql mysql        Jul   : db.opt
 -rw-r-----  root  root        Jul   : sbtest2.cfg
 -rw-r-----  mysql mysql      Jul   : sbtest2.frm
 -rw-r-----  root  root   Jul   : sbtest2.ibd
 
 //change the root.root to mysql.mysql
 
 [root@zlm3 :: /data/mysql/mysql3306/data/tt]
 #chown mysql.mysql sbtest2.*
 
 [root@zlm3 :: /data/mysql/mysql3306/data/tt]
 #ls -l
 total
 -rw-r-----  mysql mysql        Jul   : db.opt
 -rw-r-----  mysql mysql       Jul   : sbtest2.cfg
 -rw-r-----  mysql mysql      Jul   : sbtest2.frm
 -rw-r-----  mysql mysql  Jul   : sbtest2.ibd

Import the tablespace of "sbtest2" table.

 (root@localhost mysql3306.sock)[tt]>alter table sbtest2 import tablespace;
 Query OK,  rows affected,  warning (2.68 sec)
 
 (root@localhost mysql3306.sock)[tt]>show tables;
 +--------------+
 | Tables_in_tt |
 +--------------+
 | sbtest2      |
 +--------------+
  row in set (0.00 sec)
 
 (root@localhost mysql3306.sock)[tt]>select count(*) from sbtest2;
 +----------+
 | count(*) |
 +----------+
 |    |
 +----------+
  row in set (0.06 sec)
 
 --05T08::.820441Z  [Note] InnoDB: Importing tablespace for table 'sysbench/sbtest2' that was exported from host 'zlm2'
 --05T08::.820441Z  [Note] InnoDB: Phase I - Update all pages
 --05T08::.859485Z  [Note] InnoDB: Sync to disk
 --05T08::.936351Z  [Note] InnoDB: Sync to disk - done!
 --05T08::.962775Z  [Note] InnoDB: Phase III - Flush changes to disk
 --05T08::.975519Z  [Note] InnoDB: Phase IV - Flush complete
 --05T08::.975722Z  [Note] InnoDB: `tt`.`sbtest2` autoinc value set to 
 
 //The error log shows details of this import operation.

If you detach an inexistent tablespace,it will show below errors.

 (root@localhost mysql3306.sock)[tt]>alter table sbtest2 discard tablespace;
 Query OK,  rows affected (0.01 sec)
 
 (root@localhost mysql3306.sock)[tt]>alter table sbtest2 discard tablespace;
 Query OK,  rows affected,  warning (0.00 sec)
 
 (root@localhost mysql3306.sock)[tt]>show warnings;
 +---------+------+-----------------------------------------------------+
 | Level   | Code | Message                                             |
 +---------+------+-----------------------------------------------------+
 | Warning |  | InnoDB: Tablespace is missing for table tt/sbtest2. |
 +---------+------+-----------------------------------------------------+
  row in set (0.00 sec)
 
 --05T08::.055225Z  [ERROR] InnoDB: Cannot delete tablespace  because it is not found in the tablespace memory cache.
 --05T08::.055226Z  [Warning] InnoDB: Cannot delete tablespace  in DISCARD TABLESPACE: Tablespace not found
 
 //error log shows the ERROR & Warning because of the .ibd file has been deleted in first discard operation.

Copy those files to target again.

 [root@zlm2 :: /data/mysql/mysql3306/data/sysbench]
 #scp sbtest2.{ibd,cfg} zlm3:/data/mysql/mysql3306/data/tt/
 root@zlm3's password:
 sbtest2.ibd                                                                                                        %   29MB  .0MB/s   :
 sbtest2.cfg: No such file or directory
 
 //Because of "unlock tables" operation,the .cfg file has gone now.

Import the "sbtest2" tablespace again.

 (root@localhost mysql3306.sock)[tt]>alter table sbtest2 import tablespace;
 Query OK,  rows affected,  warning (2.34 sec)
 
 (root@localhost mysql3306.sock)[tt]>show warnings;
 +---------+------+--------------------------------------------------------------------------------------------------------------------------------------------+
 | Level   | Code | Message                                                                                                                                    |
 +---------+------+--------------------------------------------------------------------------------------------------------------------------------------------+
 | Warning |  | InnoDB: IO Read error: (, No such file or directory) Error opening './tt/sbtest2.cfg', will attempt to import without schema verification |
 +---------+------+--------------------------------------------------------------------------------------------------------------------------------------------+
  row in set (0.00 sec)
 
 //There's a warning about importing without .cfg file which won't impact the result.

Summary

• Transportable Tablespace(TT) of innodb provids a different way in backing up and restoring a single table between servers.
  
• TT merely supports innodb engine which can store data in tablespaces of their own by setting "innodb_file_per_table=1".
  
• TT supports importing tablespace without .cfg file what brings about us much convenience in crash recovery.
  
• Notice that there will be shared read locks on the tables after execute "flush table ... for export;" what really influences the tables need to be write.