MariaDB versus MySQL - Compatibility

MariaDB is a binary drop in replacement for MySQL

For all practical purposes, MariaDB is a binary drop in replacement of the same MySQL version (for example MySQL 5.1 -> MariaDB 5.1, MariaDB 5.2 & MariaDB 5.3 are compatible. MySQL 5.5 will be compatible with MariaDB 5.5). What this means is that:

• Data and table definition files (.frm) files are binary compatible.
• All client APIs, protocols and structs are identical.
• All filenames, binaries, paths, ports, sockets, and etc... should be the same.
• All MySQL connectors (PHP, Perl, Python, Java, .NET, MyODBC, Ruby, MySQL C connector etc) work unchanged with MariaDB.
  • There are some installation issues with PHP5 that you should be aware of (a bug in how the old PHP5 client checks library compatibility).
• The mysql-client package also works with MariaDB server.

This means that for most cases, you can just uninstall MySQL and install MariaDB and you are good to go. (No need to convert any datafiles if you use same main version, like 5.1).

We do monthly merges with the MySQL code base to ensure we keep up our compatibility and get any and all features and bug fixes Oracle adds.

We have also done a lot of work on the upgrade scripts to the point where it is now easier to upgrade from MySQL 5.0 to MariaDB 5.1 than from MySQL 5.0 to MySQL 5.1.

That said, MariaDB has a lot of new options, extension, storage engines and bug fixes that are not in MySQL. You can find the feature set for the different MariaDB versions on the What is in the different MariaDB Releases page.

See also MariaDB versus MySQL - Features.

Incompatibilities between MariaDB 5.1 and MySQL 5.1

In some few cases MariaDB has to be incompatible to allow MariaDB to provide more and better information than MySQL.

Here is the list of all known user level incompatibilities you may see when using MariaDB 5.1 instead of MySQL 5.1.

• The installation package names starts with MariaDB instead of MySQL.
• Timings may be different as MariaDB is in many cases faster than MySQL.
• mysqld in MariaDB reads also the [mariadb] sections of your my.cnf files.
• You can't use a binary only storage engine library with MariaDB if it's not compiled for exactly the same MariaDB version. (This is because the server internal structure THD is different between MySQL and MariaDB. This is common also between different MySQL versions). This should not be a problem as most people don't load new storage engines and MariaDB comes with more storage engines than MySQL.
• CHECKSUM TABLE may give different result as MariaDB doesn't ignore NULL's in the columns as MySQL 5.1 does (Future MySQL versions should calculate checksums the same way as MariaDB). You can get the 'old style' checksum in MariaDB by starting mysqld with the --old option. Note however that that the MyISAM and Aria storage engines in MariaDB are using the new checksum internally, so if you are using --old, the CHECKSUM command will be slower as it needs to calculate the checksum row by row.
• The slow query log has more information about the query, which may be a problem if you have a script which parses the slow query log.
• MariaDB by default takes a bit more memory than MySQL because we have by default enabled the Aria storage engine for handling internal temporary tables. If you need MariaDB to take very little memory (at the expense of performance), you can set the value of aria_pagecache_buffer_size to 1M (the default is 128M).
• If you are using new command options, new features of MariaDB or new storage engines, you can't move easily back and forth between MySQL and MariaDB anymore.

Incompatibilities between MariaDB 5.2 and MySQL 5.1

The list is the same as between MariaDB 5.1 and MySQL 5.1, with one addition:

• New SQL_MODE value was added: IGNORE_BAD_TABLE_OPTIONS. If it is not set, using a table, field, or index attribute (option) that is not supported by the chosen storage engine will cause an error. This change might cause warnings in the error log about incorrectly defined tables from the mysql database, fix that with mysql_upgrade.

For all practical purposes, MariaDB 5.2 is a drop in replacement for MariaDB 5.1 and MySQL 5.1.

Incompatibilities between MariaDB 5.3 and MySQL 5.1 and MariaDB 5.2

• A few error messages related to wrong conversions are different as MariaDB provides more information in the message about what went wrong.
• Error numbers for MariaDB specific errors has been moved to start from 1900 to not conflict with MySQL errors.
• Microseconds now works in all contexts; MySQL did, in some contexts, lose the microsecond part from datetime and time.
• The old --maria- startup options are removed. You should use the --aria- prefix instead. (MariaDB 5.2 supports both --maria- and --aria-)
• SHOW PROCESSLIST has an extra Progress column which shows progress for some commands. You can disable it by starting mysqld with the --old flag.
• INFORMATION_SCHEMA.PROCESSLIST has three new columns for progress reporting: STAGE, MAX_STAGE, and PROGRESS.
• Long comments which start with /*M! or /*M!##### are executed.
• If you use max_user_connections=0 (which means any number of connections) when starting mysqld, you can't change the global variable anymore while mysqld remains running. This is because when mysqld is started with max_user_connections=0 it does not allocate counting structures (which also involve a mutex for each connection). This would lead to wrong counters if you later changed the variable. If you want to be able to change this variable at runtime, set it to a high value at startup.
• You can set max_user_connections (both the global variable and the GRANT option) to -1 to stop users from connecting to the server. The global max_user_connections variable does not affect users with the SUPER privilege.
• The IGNORE directive does not ignore all errors (like fatal errors), only things that are safe to ignore.

Incompatibilities between MariaDB 5.5 and MariaDB 5.3

XtraDB

Percona, the provider of XtraDB, does not provided all earlier features of XtraDB in the 5.5 code base. Because of that, MariaDB 5.5 can't provide them either.

XtraDB options missing in 5.5

The following options are not supported by XtraDB 5.5. If you are using them in any of your my.cnf files, you should remove them before upgrading to 5.5.

• innodb_adaptive_checkpoint ; Use
• innodb_adaptive_flushing_method instead.
• innodb_auto_lru_dump ;Use
• innodb_buffer_pool_restore_at_startup instead.
• innodb_blocking_lru_restore ; Use
• innodb_blocking_buffer_pool_restore instead.
• innodb_enable_unsafe_group_commit
• innodb_expand_import ; Use
• innodb_import_table_from_xtrabackup instead.
• innodb_extra_rsegments ; Use innodb_rollback_segment
• instead.
• innodb_extra_undoslots
• innodb_fast_recovery
• innodb_flush_log_at_trx_commit_session
• innodb_overwrite_relay_log_info
• innodb_pass_corrupt_table ; Use
• innodb_corrupt_table_action instead.
• innodb_use_purge_thread
• xtradb_enhancements

XtraDB options that has changed default value

New options in XtraDB 5.5

The following new options has been added to XtraDB / InnoDB in 5.5. (Listed here just to have all XtraDB information in the same place)

• innodb_adaptive_flushing_method
• innodb_adaptive_hash_index_partitions
• innodb_blocking_buffer_pool_restore
• innodb_buffer_pool_instances
• innodb_buffer_pool_restore_at_startup
• innodb_change_buffering_debug
• innodb_corrupt_table_action
• innodb_flush_checkpoint_debug
• innodb_force_load_corrupted
• innodb_import_table_from_xtrabackup
• innodb_large_prefix
• innodb_purge_batch_size
• innodb_purge_threads
• innodb_recovery_update_relay_log
• innodb_rollback_segments
• innodb_sys_columns
• innodb_sys_fields
• innodb_sys_foreign
• innodb_sys_foreign_cols
• innodb_sys_tablestats
• innodb_use_global_flush_log_at_trx_commit
• innodb_use_native_aio

See also Perconas guide of how to upgrade to 5.5

Old, unsupported configuration options

If you are using any of the following options in your /etc/my.cnf or other my.cnf file you should remove them. This is also true for MySQL 5.1 or newer:

• skip-bdb

Replacing a MySQL RPM

If you uninstalled a MySQL RPM to install MariaDB, note that the MySQL RPM on uninstall renames /etc/my.cnf to /etc/my.cnf.rpmsave.

After installing MariaDB you should do the following to restore your old configuration options:

mv -vi /etc/my.cnf.rpmsave /etc/my.cnf