MariaDB 与 MySQL 兼容性比较

MariaDB是MySQL代码级量身定制的替代者

鉴于所有应用，MariaDB都是MySQL的代码级量身定制的替代者，相应的版本可以直接替换（如MySQL 5.1 ->MariaDB 5.1，MariaDB 5.2 &MariaDB 5.3也是兼容的。MySQL 5.5将与兼容），具体是：

• 数据及表的定义文件（.frm）在代码级兼容；
• 所有客户端的API、协议和结构都是相同的；
• 所有文件件名、二进制文件、路径、端口、套接字等……全都是一样的；
• 所有的MySQL与其他语言（PHP、Perl、Python、Java、.NET、MyODBC、Rub、MySQL C……）的连接文件无需任何改动，在MariaDB就可工作；
  • 但有些PHP5安装要点你要知道（旧的PHP5客户端库兼容性检查程序存在bug）；
• mysql-client 程序也可在MariaDB服务器上工作。

意思也就是，在大多数情况下，你只要卸载MySQL后，安装MariaDB后就可工作（在使用相同的主版本（如5.1版）的情况下，不需任何数据文件的转换）．

我们每月都会将MySQL基本代码编译入MariaDB，从而保证MariaDB与Oracle添加的任何补丁和更新的MySQL相兼容。

同时我们为了容易地从 从MySQL 5.0升级到MariaDB 5.1 ，我们在升级脚本上也做了大量的工作。

也就是说：相对于MySQL，MariaDB有更多 新选项、扩展、存储引擎及漏洞修复 ，你可以在MariaDB的不同之外页上查看详细。

MariaDB 5.1与MySQL 5.1不兼容部分

为了提供更多、更好的性能，MariaDB在有些地方与MySQL难免有所不兼容。

下面列出的是从用户使用角度，你可能看到的MariaDB 5.1与 MySQL 5.1不同之外。

• 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 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 theAria 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 usingnew command options, new features of MariaDB ornew storage engines, you can't move easily back and forth between MySQL and MariaDB anymore.

MariaDB 5.2与MySQL 5.1不兼容部分

The list is the same as betweenMariaDB 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 forMariaDB 5.1 and MySQL 5.1.

MariaDB 5.3与MySQL 5.1、MariaDB 5.2不兼容部分

• 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.
• MariaDB does more strict 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 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.
• TheIGNORE directive does not ignore all errors (like fatal errors), only things that are safe to ignore.

MariaDB 5.5 与MariaDB 5.3不兼容部分

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

旧的、也不支持的配置选项

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