See also MariaDB vs MySQL - Features
Until MariaDB 5.5, MariaDB versions functioned as a "drop-in replacement" for the equivalent MySQL version, with some limitations. From MariaDB 10.0, it is usually still very easy to upgrade from MySQL.
MariaDB's data files are generally binary compatible with those from the equivalent MySQL version.
All filenames and paths are generally the same.
Data and table definition files (.frm) files are binary compatible.
See note below for an incompatibility with views!
MariaDB's client protocol is binary compatible with MySQL's client protocol.
All client APIs and structs are identical.
All ports and sockets are generally the same.
All MySQL connectors (PHP, Perl, Python, Java, .NET, MyODBC, Ruby, MySQL C connector etc) work unchanged with MariaDB.
This means that for many cases, you can just uninstall MySQL and install MariaDB and you are good to go. There is not generally any need to convert any data files.
However, you must 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.
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.
Drop-in Compatibility of Specific MariaDB VersionsMariaDB 10.2, MariaDB 10.3, and MariaDB 10.4 function as limited drop-in replacements for MySQL 5.7, as far as InnoDB is concerned. However, the implementation differences continue to grow in each new MariaDB version.
MariaDB 10.0 and MariaDB 10.1 function as limited drop-in replacements for MySQL 5.6, as far as InnoDB is concerned. However, there are some implementation differences in some features.
MariaDB 5.5 functions as a drop-in replacement for MySQL 5.5.
MariaDB 5.1, MariaDB 5.2, and MariaDB 5.3 function as drop-in replacements for MySQL 5.1.
Replication CompatibilitySee Replication Compatibility Between MariaDB and MySQL.
Incompatibilities between Currently Maintained MariaDB Versions and MySQL Incompatibilities between MariaDB Rolling and MySQL 8.0For unmaintained versions, see:
MariaDB 10.1 and above does not support MySQL 5.7's packed JSON objects. MariaDB follows the SQL standard and stores the JSON as a normal TEXT/BLOB. If you want to replicate JSON columns from MySQL to MariaDB, you should store JSON objects in MySQL in a TEXT column or use statement based replication. If you are using JSON columns and want to upgrade to MariaDB, you can either convert the JSON columns to TEXT or use mysqldump to copy these tables to MariaDB. In MySQL, JSON is compared according to json values. In MariaDB JSON strings are normal strings and compared as strings.
MariaDB 10.1's InnoDB encryption is implemented differently than MySQL 5.7's InnoDB encryption.
MariaDB does not support MySQL 5.7's X protocol.
MariaDB 10.1 does not support the use of multiple triggers of the same type for a table. This feature was introduced in MariaDB 10.2.2.
MariaDB 10.1 does not support MySQL 5.7's transportable tablespaces for partitioned InnoDB tables. ALTER TABLE ... {DISCARD|IMPORT} PARTITION is not supported. For a workaround see the following blog post .
MariaDB 10.1 does not support MySQL 5.7's online undo tablespace truncation. However, this feature was added to MariaDB 10.2.
MySQL 5.7 features a new implementation of the performance_schema and a sys schema wrapper. These are not yet supported in MariaDB.
MySQL 5.7 adds group replication. This feature is incompatible with MariaDB's galera-cluster replication.
MariaDB 10.1 does not support MySQL 5.7's, ACCOUNT LOCK/UNLOCK synax for CREATE USER and ALTER USER statements.
MariaDB 10.1 does not support MySQL 5.7's ALTER TABLE...RENAME INDEX statements.
MariaDB 10.1 does not support MySQL 5.7's {WITH|WITHOUT} VALIDATION syntax for ALTER TABLE.. EXCHANGE PARTITION statements.
Also see 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. However MariaDB 10.0 can be a slave of MySQL 5.6 or any earlier MySQL/MariaDB version. Note that MariaDB and MySQL also have different GTID system variables, so these need to be adjusted when migrating.
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.
MySQL 5.6 has performance schema enabled by default. For performance reasons MariaDB 10.0 has it disabled by default. You can enable it by starting mysqld with the option --performance-schema.
MariaDB 10.0 does not support the MySQL Memcached plugin. However, data stored using memcached can be retrieved because the data is stored as InnoDB tables. MariaDB is able to start successfully with an error message of not being able to find libmemcached.so library.
Users created with MySQL's SHA256 password algorithm cannot be used in MariaDB 10.0 as MariaDB does not include MySQL's sha256_password plugin.
MariaDB implements some changes in the SQL query optimizer over what's available in MySQL. This can result in EXPLAIN statements showing different plans.
Views with definition ALGORITHM=MERGE or ALGORITHM=TEMPTABLE got accidentally swapped between MariaDB and MySQL! You have to re-create views created with either of these definitions!
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).
Before MariaDB 5.5.31, X'HHHH', the standard SQL syntax for binary string literals, erroneously worked in the same way as 0xHHHH, which could work as a number or string depending on the context. In 5.5.31 this was fixed to behave as a string in all contexts (and never as a number), introducing an incompatibility with previous versions of MariaDB, and all versions of MySQL. See CAST and Hexadecimal Literals for more details and examples.
As of MariaDB 5.5.35, EXTRACT (HOUR FROM ...) adheres to the SQL standard and returns a result from 0 to 23. In MySQL, and earlier versions of MariaDB, the result can be greater than 23.
Views with definition ALGORITHM=MERGE or ALGORITHM=TEMPTABLE got accidentally swapped between MariaDB 5.2 and MariaDB 5.3! You have to re-create views created with either of these definitions!
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.
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.
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.
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 withmore 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 hasmore 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 any of the following options in your /etc/my.cnf or othermy.cnf file you should remove them. This is also true for MySQL 5.1 or newer:
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.cnfA 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.
Another option is to use the MariaDB MaxScale proxy, that works with both MySQL and MariaDB.
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