14.2.1.1. `InnoDB` as the Default MySQL Storage Engine

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.

Trends in Storage Engine Usage

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 14.2.3.13.3, "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 14.2.4.2.3, "Optimizations for Read-Only Transactions" for details.
Applications distributed on read-only media can now use InnoDB tables. See Section 14.2.5.1, "Support for Read-Only Media" for details.

Consequences of InnoDB as Default MySQL Storage Engine

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 InnoDB.)

The mysql and information_schema databases, that implement some of the MySQL internals, still use MyISAM. In particular, you cannot switch the grant tables to use InnoDB.

Benefits of InnoDB Tables

If you use MyISAM tables but aren't tied to them for technical reasons, you'll find many things more convenient when you use 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 in WHERE clauses, ORDER BY clauses, GROUP BY clauses, and join operations.
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.

Best Practices for InnoDB Tables

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 story short:

Specify a primary key for every table using the most frequently queried column or columns, or anauto-increment value if there is no obvious primary key.
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 operations into transactions, by 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 INSERT, UPDATE, or DELETE statements that run for hours without committing.
Stop using 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 the SELECT ... FOR UPDATE syntax to lock just the rows you intend to update.
Enable the innodb_file_per_table option to put the data and indexes for individual tables into separate files, instead of in a single giant system tablespace. (This setting is required to use some of the other features, such as table compression and fast truncation.)
Evaluate whether your data and access patterns benefit from the new InnoDB table compression feature (ROW_FORMAT=COMPRESSED on the CREATE 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 CREATE TABLE.

Recent Improvements for InnoDB Tables

If you have experience with InnoDB, but from MySQL 5.1 or earlier, read about the latest InnoDB enhancements in Section 14.2.4.2, "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 DYNAMIC row format.
You can monitor the internal workings of the storage engine by querying INFORMATION_SCHEMA tables.
You can monitor the performance details of the storage engine by querying performance_schema tables.
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 14.2.4.2, "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".

Testing and Benchmarking with InnoDB as Default Storage Engine

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 my.cnf file 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 CREATE TABLE statement to avoid the error. (For example, tables that rely on full-text search must be MyISAM tables rather than InnoDB ones.)

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 ALTER TABLE 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.

Verifying that InnoDB is the Default Storage Engine

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 skip-innodb option.

14.2.1.1. InnoDB as the Default MySQL Storage Engine