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== 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|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
[[getting-installing-and-upgrading-mariadb|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
[[upgrading-to-mariadb-from-mysql|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
[[mariadb-versus-mysql-features|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|What is in the different MariaDB Releases]] page.
See also [[mariadb-versus-mysql-features | 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 <<code>>[mariadb]<</code>> 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
[[mariadb-storage-engines|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 <<code>>--old<</code>> option. Note however that that
the MyISAM and Aria storage engines in MariaDB are using the new checksum
internally, so if you are using <<code>>--old<</code>>, the ##CHECKSUM## command will be
slower as it needs to calculate the checksum row by row.
* The slow query log has
[[slow-query-log-extended-statistics|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-formerly-known-as-maria|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 [[mysqld-startup-options|new command options]],
[[mariadb-versus-mysql-features|new features of MariaDB]] or
[[mariadb-storage-engines|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 <<code>>SQL_MODE<</code>> value was added:
<<code>>IGNORE_BAD_TABLE_OPTIONS<</code>>. 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 <<code>>mysql<</code>>
database, fix that with <<code>>mysql_upgrade<</code>>.
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 <<code>>--maria-<</code>> startup options are removed. You should use
the <<code>>--aria-<</code>> prefix instead. (MariaDB 5.2 supports both <<code>>--maria-<</code>>
and <<code>>--aria-<</code>>)
* ##[[show-processlist|SHOW PROCESSLIST]]## has an extra ##Progress## column
which shows progress for some commands. You can disable it by
starting ##mysqld## with the <<code>>--old<</code>> flag.
* ##INFORMATION_SCHEMA.PROCESSLIST## has three new columns for progress
reporting: ##STAGE##, ##MAX_STAGE##, and ##PROGRESS##.
* [[comment-syntax|Long comments]] which start with <<code>>/*M!<</code>>
or <<code>>/*M!#####<</code>> are executed.
* If you use <<code>>max_user_connections=0<</code>> (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 <<code>>max_user_connections=0<</code>> 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 <<code>>max_user_connections<</code>> (both the global variable
and the ##GRANT## option) to ##-1## to stop users from connecting to the
server. The global <<code>>max_user_connections<</code>> variable does not
affect users with the <<code>>SUPER<</code>> privilege.
* The [[ignore|IGNORE]] directive does not ignore all errors (like fatal errors), only things that are safe to ignore.
== 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:
<<code>>
mv -vi /etc/my.cnf.rpmsave /etc/my.cnf
<</code>>
