Here is a more complete answer with regard to InnoDB. It is a bit of a lengthy process, but can be worth the effort.
Keep in mind that /var/lib/mysql/ibdata1
is the busiest file in the InnoDB infrastructure. It normally houses six types of information:
Table Data
Table Indexes
Rollback Segments
Undo Space
Table Metadata (Data Dictionary)
Double Write Buffer (background writing to prevent reliance on OS caching)
Insert Buffer (managing changes to non-unique secondary indexes)
InnoDB Architecture
Many people create multiple ibdata
files hoping for better disk-space management and performance, however that belief is mistaken.
Can I run OPTIMIZE TABLE
?
Unfortunately, running OPTIMIZE TABLE
against an InnoDB table stored in the shared table-space file ibdata1
does two things:
Makes the table’s data and indexes contiguous inside
ibdata1
Makes
ibdata1
grow because the contiguous data and index pages are appended toibdata1
You can however, segregate Table Data and Table Indexes from ibdata1
and manage them independently.
Can I run OPTIMIZE TABLE
with innodb_file_per_table
?
Suppose you were to add innodb_file_per_table
to /etc/my.cnf (my.ini)
. Can you then just run OPTIMIZE TABLE
on all the InnoDB Tables?
Good News : When you run OPTIMIZE TABLE
with innodb_file_per_table
enabled, this will produce a .ibd
file for that table. For example, if you have table mydb.mytable
witha datadir of /var/lib/mysql
, it will produce the following:
/var/lib/mysql/mydb/mytable.frm
/var/lib/mysql/mydb/mytable.ibd
The .ibd
will contain the Data Pages and Index Pages for that table. Great.
Bad News : All you have done is extract the Data Pages and Index Pages of mydb.mytable
from living in ibdata
. The data dictionary entry for every table, including mydb.mytable
, still remains in the data dictionary (See the Pictorial Representation of ibdata1). YOU CANNOT JUST SIMPLY DELETE ibdata1
AT THIS POINT !!! Please note that ibdata1
has not shrunk at all.
InnoDB Infrastructure Cleanup
To shrink ibdata1
once and for all you must do the following:
Dump (e.g., with
mysqldump
) all databases into a.sql
text file (SQLData.sql
is used below)Drop all databases (except for
mysql
andinformation_schema
) CAVEAT : As a precaution, please run this script to make absolutely sure you have all user grants in place:mkdir /var/lib/mysql_grants cp /var/lib/mysql/mysql/* /var/lib/mysql_grants/. chown -R mysql:mysql /var/lib/mysql_grants
Login to mysql and run
SET GLOBAL innodb_fast_shutdown = 0;
(This will completely flush all remaining transactional changes fromib_logfile0
andib_logfile1
)Shutdown MySQL
Add the following lines to
/etc/my.cnf
(ormy.ini
on Windows)[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 sureinnodb_log_file_size
is 25% ofinnodb_buffer_pool_size
.Also: innodb_flush_method=O_DIRECT is not available on Windows)
Delete
ibdata*
andib_logfile*
, Optionally, you can remove all folders in/var/lib/mysql
, except/var/lib/mysql/mysql
.Start MySQL (This will recreate
ibdata1
[10MB by default] andib_logfile0
andib_logfile1
at 1G each).Import
SQLData.sql
Now, ibdata1
will still grow but only contain table metadata because each InnoDB table will exist outside of ibdata1
. ibdata1
will no longer contain InnoDB data and indexes for other tables.
For example, suppose you have an InnoDB table named mydb.mytable
. If you look in /var/lib/mysql/mydb
, you will see two files representing the table:
mytable.frm
(Storage Engine Header)mytable.ibd
(Table Data and Indexes)
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 shrank a 50GB ibdata1
file down to only 500MB!
Give it a try. If you have further questions on this, just ask. Trust me; this will work in the short term as well as over the long haul.
CAVEAT
At Step 6, if mysql cannot restart because of the mysql
schema begin dropped, look back at Step 2. You made the physical copy of the mysql
schema. You can restore it as follows:
mkdir /var/lib/mysql/mysql
cp /var/lib/mysql_grants/* /var/lib/mysql/mysql
chown -R mysql:mysql /var/lib/mysql/mysql
Go back to Step 6 and continue