The busiest file in the InnoDB infrastructure is /var/lib/mysql/ibdata1
This file normally houses many classes of information (when innodb_file_per_table is 0)
- Table Data
- Table Indexes
- MVCC (Multiversioning Concurrency Control) Data
- Rollbacks Segments
- Undo Tablespace
- Table Metadata
Many people create multiple ibdata files hoping for better diskspace management and performance. It does not help.
Unfortunately, OPTIMIZE TABLE against an InnoDB table stored in ibdata1 does two things:
- Makes the table’s data and indexes contiguous inside ibdata1
- It makes ibdata1 grow because the contiguous data is appended to ibdata1
You can segregate Table Data and Table Indexes from ibdata1 and manage them independently using innodb_file_per_table. To shrink ibdata1 once and for all you must do the following
Step 01) MySQLDump all databases into a SQL text file (call it SQLData.sql)
Step 02) Drop all databases (except mysql schema)
Step 03) Shutdown mysql
Step 04) Add the following lines to /etc/my.cnf
[mysqld] innodb_file_per_table innodb_flush_method=O_DIRECT innodb_log_file_size=1G innodb_buffer_pool_size=4G
Sidenote: Whatever your set for innodb_buffer_pool_size, make sure innodb_log_file_size is 25% of innodb_buffer_pool_size.
Step 05) Delete ibdata1, ib_logfile0 and ib_logfile1
At this point, there should only be the mysql schema in /var/lib/mysql
Step 06) Restart mysql
This will recreate ibdata1 at 10MB, ib_logfile0 and ib_logfile1 at 1G each
Step 07) Reload SQLData.sql into mysql
ibdata1 will grow but only contain table metadata
Each InnoDB table will exist outside of ibdata1
Suppose you have an InnoDB table named mydb.mytable. If you go into /var/lib/mysql/mydb, you will see two files representing the table
- mytable.frm (Storage Engine Header)
- mytable.ibd (Home of Table Data and Table Indexes for mydb.mytable)
ibdata1 will never contain InnoDB data and Indexes anymore.
With the innodb_file_per_table option in /etc/my.cnf, you can run
OPTIMIZE TABLE mydb.mytable and the file
/var/lib/mysql/mydb/mytable.ibd will actually shrink.
I have done this many times in my career as a MySQL DBA
In fact, the first time I did this, I collapsed a 50GB ibdata1 file into 500MB.
Give it a try. If you have further questions on this, email me. Trust me. This will work in the short term and over the long haul. !!!
If you would like to see how much actual data is stored in MyISAM and InnoDB, please run this query:
SELECT IFNULL(B.engine,'Total') "Storage Engine", CONCAT(LPAD(REPLACE(FORMAT(B.DSize/POWER(1024,pw),3),',',''),17,' '),' ', SUBSTR(' KMGTP',pw+1,1),'B') "Data Size", CONCAT(LPAD(REPLACE( FORMAT(B.ISize/POWER(1024,pw),3),',',''),17,' '),' ', SUBSTR(' KMGTP',pw+1,1),'B') "Index Size", CONCAT(LPAD(REPLACE( FORMAT(B.TSize/POWER(1024,pw),3),',',''),17,' '),' ', SUBSTR(' KMGTP',pw+1,1),'B') "Table Size" FROM (SELECT engine,SUM(data_length) DSize,SUM(index_length) ISize, SUM(data_length+index_length) TSize FROM information_schema.tables WHERE table_schema NOT IN ('mysql','information_schema','performance_schema') AND engine IS NOT NULL GROUP BY engine WITH ROLLUP) B, (SELECT 3 pw) A ORDER BY TSize;
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