SkySQL has a MariaDB vs MySQL whitepaper available for download.

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.
  • The mysql-client package also works with MariaDB server.
  • The shared client library is binary compatible with MySQL's client library.

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). You must however still run mysql_upgrade to finish the upgrade. This is needed to ensure that your mysql privilege and event tables are updated with the new fields MariaDB uses.

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.

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 start with MariaDB instead of MySQL.
  • Timings may be different as MariaDB is in many cases faster than MySQL.
  • mysqld in MariaDB also reads 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:

  • A 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 have been moved to start from 1900 so as not to conflict with MySQL errors.
  • Microseconds now work in all contexts; MySQL, in some contexts, lost the microsecond part from datetime and time.
  • UNIX_TIMESTAMP(constant-date-string) returns a timestamp with 6 decimals in MariaDB while MySQL returns it without a decimal. This can cause a problem if you are using UNIX_TIMESTAMP() as a partitioning function. You can fix this by using FLOOR(UNIX_TIMESTAMP(..)) or changing the date string to a date number, like 20080101000000.
  • MariaDB performs stricter checking of date, datetime and timestamp values. For example UNIX_TIMESTAMP('x') now returns NULL instead of 0.
  • 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 either --old-mode=NO_PROGRESS_INFO or with the --old flag (see OLD_MODE).
  • 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 provide all earlier XtraDB features 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.

XtraDB options that have changed default value

OptionOld valueNew value
innodb_change_bufferinginserts all
innodb_flush_neighbor_pages1 area

New options in XtraDB 5.5

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

See also Perconas guide of how to upgrade to 5.5

Incompatibilities between MariaDB 5.5 and MariaDB 5.3 and MySQL 5.5

  • INSERT IGNORE also gives warnings for duplicate key errors. You can turn this off by setting OLD_MODE=NO_DUP_KEY_WARNINGS_WITH_IGNORE (see OLD_MODE).

Incompatibilities between MariaDB 10.0 and MySQL 5.6

  • All MySQL binaries (mysqld, myisamchk etc.) give a warning if one uses a prefix of an option (such as --big-table instead of --big-tables). MariaDB binaries work in the same way as most other Unix commands and don't give warnings when using unique prefixes.
  • MariaDB GTID is not compatible with MySQL 5.6. This means that one can't have MySQL 5.6 as a slave for MariaDB 10.0
  • To make CREATE TABLE ... SELECT work the same way in statement based and row based replication it's by default executed as CREATE OR REPLACE TABLE on the slave. One benefit of this is that if the slave dies in the middle of CREATE ... SELECT it will be able to continue.
    • One can use the slave-ddl-exec-mode variable to specify how CREATE TABLE and DROP TABLE is replicated.

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

Incompatibilities between MariaDB and MySQL-Proxy

A MySQL client API is able to connect to MariaDB using MySQL-Proxy but a MariaDB client API will receive progress reporting informations that MySQL-Proxy does not implement, to get full compatibility in all case just disable progress reporting on the client or server side.

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