Do not convert MySQL system tables in the
mysql database from
InnoDB tables! This is an unsupported
operation. If you do this, MySQL does not restart until you
restore the old system tables from a backup or re-generate them
with the mysql_install_db script.
A table cannot contain more than 1000 columns.
InnoDB internal maximum key length is
3500 bytes, but MySQL itself restricts this to 1024 bytes.
Index key prefixes can be up to 767 bytes (255 bytes before
MySQL 4.1.2). See Section 12.1.4, “
CREATE INDEX Syntax”.
The maximum row length, except for variable-length columns
TEXT), is slightly less than
half of a database page. That is, the maximum row length is
about 8000 bytes.
columns must be less than 4GB, and the total row length,
TEXT columns, must be less than
If a row is less than half a page long, all of it is stored locally within the page. If it exceeds half a page, variable-length columns are chosen for external off-page storage until the row fits within half a page, as described in Section 126.96.36.199, “File Space Management”.
On some older operating systems, files must be less than 2GB.
This is not a limitation of
but if you require a large tablespace, you will need to
configure it using several smaller data files rather than one
or a file large data files.
The combined size of the
InnoDB log files
must be less than 4GB.
The minimum tablespace size is 10MB. The maximum tablespace size is four billion database pages (64TB). This is also the maximum size for a table.
InnoDB tables do not support
InnoDB tables do not support spatial data
ANALYZE TABLE determines index
cardinality (as displayed in the
Cardinality column of
SHOW INDEX output) by doing
eight random dives to each of the index trees and updating
index cardinality estimates accordingly. Because these are
only estimates, repeated runs of
TABLE may produce different numbers. This makes
ANALYZE TABLE fast on
InnoDB tables but not 100% accurate because
it does not take all rows into account.
MySQL uses index cardinality estimates only in join
optimization. If some join is not optimized in the right way,
you can try using
TABLE. In the few cases that
ANALYZE TABLE does not produce
values good enough for your particular tables, you can use
FORCE INDEX with your queries to force the
use of a particular index, or set the
variable to ensure that MySQL prefers index lookups over table
scans. See Section 5.1.3, “Server System Variables”, and
Section B.5.6, “Optimizer-Related Issues”.
SHOW TABLE STATUS does not give
accurate statistics on
except for the physical size reserved by the table. The row
count is only a rough estimate used in SQL optimization.
InnoDB does not keep an internal count of
rows in a table. (In practice, this would be somewhat
complicated due to multi-versioning.) To process a
SELECT COUNT(*) FROM t statement,
InnoDB must scan an index of the table,
which takes some time if the index is not entirely in the
buffer pool. If your table does not change often, using the
MySQL query cache is a good solution. To get a fast count, you
have to use a counter table you create yourself and let your
application update it according to the inserts and deletes it
SHOW TABLE STATUS also
can be used if an approximate row count is sufficient. See
Section 188.8.131.52, “
InnoDB Performance Tuning Tips”.
InnoDB always stores database
and table names internally in lowercase. To move databases in
a binary format from Unix to Windows or from Windows to Unix,
you should create all databases and tables using lowercase
AUTO_INCREMENT column, you must
always define an index for the table, and that index must
contain just the
AUTO_INCREMENT column. In
MyISAM tables, the
AUTO_INCREMENT column may be part of a
Before MySQL 4.1.12,
InnoDB does not
AUTO_INCREMENT table option for
setting the initial sequence value in an
ALTER TABLE statement. Before
MySQL 4.1.14, the same is true for
TABLE. To set the value with
InnoDB, insert a dummy row with a value one
less and delete that dummy row, or insert the first row with
an explicit value specified.
While initializing a previously specified
AUTO_INCREMENT column on a table,
InnoDB sets an exclusive lock on the end of
the index associated with the
AUTO_INCREMENT column. In accessing the
InnoDB uses a
specific table lock mode
AUTO-INC where the
lock lasts only to the end of the current SQL statement, not
to the end of the entire transaction. Other clients cannot
insert into the table while the
table lock is held; see
Section 184.108.40.206, “
AUTO_INCREMENT Handling in
When you restart the MySQL server,
may reuse an old value that was generated for an
AUTO_INCREMENT column but never stored
(that is, a value that was generated during an old transaction
that was rolled back).
AUTO_INCREMENT column runs out of
InnoDB wraps a
BIGINT values have 64 bits, so
if you were to insert one million rows per second, it would
still take nearly three hundred thousand years before
BIGINT reached its upper bound.
With all other integer type columns, a duplicate-key error
results. This is similar to how
works, because it is mostly general MySQL behavior and not
about any storage engine in particular.
regenerate the table but instead deletes all rows, one by one.
Under some conditions,
InnoDB table is mapped to
FROM and does
not reset the
AUTO_INCREMENT counter. See
Section 12.1.10, “
TRUNCATE TABLE Syntax”.
Before MySQL 4.0.14 or 4.1.0, if you tried to create a unique index on a prefix of a column you got an error:
CREATE TABLE T (A CHAR(20), B INT, UNIQUE (A(5))) TYPE = InnoDB;
If you created a nonunique index on a prefix of a column,
InnoDB created an index over the whole
column. These restrictions were removed in MySQL 4.0.14.
Before MySQL 4.0.20 or 4.1.2, the MySQL
LOCK TABLES operation does not
InnoDB row-level locks set by
completed SQL statements. This means that you can get a table
lock on a table even if there still exist transactions by
other users who have row-level locks on the same table. Thus,
your operations on the table may have to wait if they collide
with these locks of other users. Also a deadlock is possible.
However, this does not endanger transaction integrity, because
the row-level locks set by
take care of the integrity. Also, a table lock prevents other
transactions from acquiring more row-level locks (in a
conflicting lock mode) on the table.
Beginning with MySQL 4.0.20 and 4.1.2, the MySQL
LOCK TABLES operation acquires
two locks on each table if
innodb_table_locks=1 (the default). In
addition to a table lock on the MySQL layer, it also acquires
InnoDB table lock. Older versions of
MySQL do not acquire
InnoDB table locks.
Beginning with MySQL 4.0.22 and 4.1.7, the old behavior can be
selected by setting
InnoDB table lock is acquired,
LOCK TABLES completes even if
some records of the tables are being locked by other
InnoDB locks held by a transaction are
released when the transaction is committed or aborted. Thus,
it does not make much sense to invoke
LOCK TABLES on
InnoDB tables in
autocommit = 1 mode, because
InnoDB table locks would be
Sometimes it would be useful to lock further tables in the
course of a transaction. Unfortunately,
LOCK TABLES in MySQL performs
InnoDB variant of
LOCK TABLES has been planned
that can be executed in the middle of a transaction.
Before MySQL 3.23.52, replication always ran with autocommit enabled. Therefore consistent reads in the slave would also see partially processed transactions, and thus the read would not be really consistent in the slave. This restriction was removed in MySQL 3.23.52.
LOAD TABLE FROM MASTER
statement for setting up replication slave servers does not
InnoDB tables. A workaround is to
alter the table to
MyISAM on the master,
then do the load, and after that alter the master table back
InnoDB. Do not do this if the tables use
InnoDB-specific features such as foreign
The default database page size in
16KB. By recompiling the code, you can set it to values
ranging from 8KB to 64KB. You must update the values of
UNIV_PAGE_SIZE_SHIFT in the
univ.i source file.
Changing the page size is not a supported operation and
there is no guarantee that
InnoDB will function normally
with a page size other than 16KB. Problems compiling or
running InnoDB may occur.
A version of
InnoDB built for
one page size cannot use data files or log files from a
version built for a different page size.
You cannot create a table with a column name that matches the
name of an internal InnoDB column (including
DB_MIX_ID). In versions of MySQL before
4.1.19 this would cause a crash, since 4.1.19 the server will
report error 1005 and refers to error –1 in the error
message. This limitation applies only to use of the names in
InnoDB has a limit of 1023 concurrent
transactions that have created undo records by modifying data.
Workarounds include keeping transactions as small and fast as
possible and delaying changes until near the end of the
transaction. Applications should commit transactions before
doing time-consuming client-side operations.