MySQL has a well-earned reputation for being easy-to-use and delivering performance and scalability. In previous versions of MySQL, MyISAM was the default storage engine. In our experience, most users never changed the default settings. With MySQL 5.5, InnoDB becomes the default storage engine. Again, we expect most users will not change the default settings. But, because of InnoDB, the default settings deliver the benefits users expect from their RDBMS: ACID Transactions, Referential Integrity, and Crash Recovery. Let's explore how using InnoDB tables improves your life as a MySQL user, DBA, or developer.
In the first years of MySQL growth, early web-based applications didn't push the limits of concurrency and availability. In 2010, hard drive and memory capacity and the performance/price ratio have all gone through the roof. Users pushing the performance boundaries of MySQL care a lot about reliability and crash recovery. MySQL databases are big, busy, robust, distributed, and important.
InnoDB hits the sweet spot of these top user priorities. The trend of storage engine usage has shifted in favor of the more scalable InnoDB. Thus MySQL 5.5 is the logical transition release to make InnoDB the default storage engine.
MySQL continues to work on addressing use cases that formerly required MyISAM tables. In MySQL 5.6 and higher:
InnoDB can perform full-text search using the
FULLTEXT index type. See
Section 22.214.171.124.3, “
FULLTEXT Indexes” for details.
InnoDB now performs better with read-only or read-mostly
workloads. Automatic optimizations apply to InnoDB queries in
autocommit mode, and you
can explicitly mark transactions as read-only with the syntax
START TRANSACTION READ ONLY. See
Section 126.96.36.199.3, “Optimizations for Read-Only Transactions” for details.
Applications distributed on read-only media can now use InnoDB tables. See Section 188.8.131.52, “Support for Read-Only Media” for details.
Starting from MySQL 5.5.5, the default storage engine for new tables
is InnoDB. This change applies to newly created tables that don't
specify a storage engine with a clause such as
ENGINE=MyISAM. (Given this change of default
behavior, MySQL 5.5 might be a logical point to evaluate whether
your tables that do use MyISAM could benefit from switching to
information_schema databases, that implement some
of the MySQL internals, still use MyISAM. In particular, you cannot
switch the grant tables to use InnoDB.
If you use
MyISAM tables but aren't tied to them
for technical reasons, you'll find many things more convenient when
InnoDB tables in MySQL 5.5:
If your server crashes because of a hardware or software issue, regardless of what was happening in the database at the time, you don't need to do anything special after restarting the database. InnoDB crash recovery automatically finalizes any changes that were committed before the time of the crash, and undoes any changes that were in process but not committed. Just restart and continue where you left off. This process is now much faster than in MySQL 5.1 and earlier.
The InnoDB buffer pool caches table and index data as the data is accessed. Frequently used data is processed directly from memory. This cache applies to so many types of information, and speeds up processing so much, that dedicated database servers assign up to 80% of their physical memory to the InnoDB buffer pool.
If you split up related data into different tables, you can set up foreign keys that enforce referential integrity. Update or delete data, and the related data in other tables is updated or deleted automatically. Try to insert data into a secondary table without corresponding data in the primary table, and the bad data gets kicked out automatically.
If data becomes corrupted on disk or in memory, a checksum mechanism alerts you to the bogus data before you use it.
When you design your database with appropriate
primary key columns for
each table, operations involving those columns are automatically
optimized. It is very fast to reference the primary key columns
GROUP BY clauses, and
Inserts, updates, deletes are optimized by an automatic mechanism called change buffering. InnoDB not only allows concurrent read and write access to the same table, it caches changed data to streamline disk I/O.
Performance benefits are not limited to giant tables with long-running queries. When the same rows are accessed over and over from a table, a feature called the Adaptive Hash Index takes over to make these lookups even faster, as if they came out of a hash table.
If you have been using
InnoDB for a long time,
you already know about features like transactions and foreign keys.
If not, read about them throughout this chapter. To make a long
Embrace the idea of joins, where data is pulled from multiple tables based on identical ID values from those tables. For fast join performance, define foreign keys on the join columns, and declare those columns with the same data type in each table. The foreign keys also propagate deletes or updates to all affected tables, and prevent insertion of data in a child table if the corresponding IDs are not present in the parent table.
Turn off autocommit. Committing hundreds of times a second puts a cap on performance (limited by the write speed of your storage device).
Group sets of related DML
bracketing them with
START TRANSACTION and
COMMIT statements. While you don't want to
commit too often, you also don't want to issue huge batches of
DELETE statements that run for hours without
LOCK TABLE statements. InnoDB can
handle multiple sessions all reading and writing to the same
table at once, without sacrificing reliability or high
performance. To get exclusive write access to a set of rows, use
SELECT ... FOR UPDATE syntax to lock just
the rows you intend to update.
innodb_file_per_table option to
put the data and indexes for individual tables into separate
files, instead of in a single giant
(This setting is required to use some of the other features,
such as table
compression and fast
Evaluate whether your data and access patterns benefit from the
new InnoDB table
ROW_FORMAT=COMPRESSED on the
TABLE statement. You can compress InnoDB tables
without sacrificing read/write capability.
Run your server with the option
--sql_mode=NO_ENGINE_SUBSTITUTION to prevent
tables being created with a different storage engine if there is
an issue with the one specified in the
ENGINE= clause of
If you have experience with InnoDB, but from MySQL 5.1 or earlier,
read about the latest InnoDB enhancements in
Section 184.108.40.206, “
InnoDB Performance and Scalability Enhancements” and
Section 14.2.5, “
InnoDB Features for Flexibility, Ease of Use and
Reliability”. To make a long story short:
You can compress tables and associated indexes.
You can create and drop indexes with much less performance or availability impact than before.
Truncating a table is very fast, and can free up disk space for the operating system to reuse, rather than freeing up space within the system tablespace that only InnoDB could reuse.
The storage layout for table data is more efficient for BLOBs
and long text fields, with the
You can monitor the internal workings of the storage engine by
You can monitor the performance details of the storage engine by
There are many many performance improvements. In particular, crash recovery, the automatic process that makes all data consistent when the database is restarted, is fast and reliable. (Now much much faster than long-time InnoDB users are used to.) The bigger the database, the more dramatic the speedup.
Most new performance features are automatic, or at most require
setting a value for a configuration option. For details, see
Section 220.127.116.11, “
InnoDB Performance and Scalability Enhancements”. For InnoDB-specific tuning
techniques you can apply in your application code, see
Section 8.5, “Optimizing for
InnoDB Tables”. Advanced users can review
Section 14.2.6, “
InnoDB Startup Options and System Variables”.
Even before completing your upgrade from MySQL 5.1 or earlier to
MySQL 5.5 or higher, you can preview whether your database server or
application works correctly with InnoDB as the default storage
engine. To set up InnoDB as the default storage engine with an
earlier MySQL release, either specify on the command line
--default-storage-engine=InnoDB, or add to your
default-storage-engine=innodb in the
[mysqld] section, then restart the server.
Since changing the default storage engine only affects new tables as
they are created, run all your application installation and setup
steps to confirm that everything installs properly. Then exercise
all the application features to make sure all the data loading,
editing, and querying features work. If a table relies on some
MyISAM-specific feature, you'll receive an error; add the
ENGINE=MyISAM clause to the
TABLE statement to avoid the error. (For example, tables
that rely on full-text search must be MyISAM tables rather than
If you did not make a deliberate decision about the storage engine,
and you just want to preview how certain tables work when they're
created under InnoDB, issue the command
table_name ENGINE=InnoDB; for each table. Or, to run test
queries and other statements without disturbing the original table,
make a copy like so:
CREATE TABLE InnoDB_Table (...) ENGINE=InnoDB AS SELECT * FROM MyISAM_Table;
Since there are so many performance enhancements in InnoDB in MySQL 5.5 and higher, to get a true idea of the performance with a full application under a realistic workload, install the latest MySQL server and run benchmarks.
Test the full application lifecycle, from installation, through heavy usage, and server restart. Kill the server process while the database is busy to simulate a power failure, and verify that the data is recovered successfully when you restart the server.
Test any replication configurations, especially if you use different MySQL versions and options on the master and the slaves.
To know what the status of InnoDB is, whether you're doing what-if testing with an older MySQL or comprehensive testing with the latest MySQL:
Issue the command
SHOW ENGINES; to see all
the different MySQL storage engines. Look for
DEFAULT in the InnoDB line.
If InnoDB is not present at all, you have a
mysqld binary that was compiled without
InnoDB support and you need to get a different one.
If InnoDB is present but disabled, go back through your startup
options and configuration file and get rid of any