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13.5.7. Maria Design Notes

Maria supports all aspects of MyISAM, except as noted below. This includes external and internal check/repair/compressing of rows, different row formats, different index compress formats, maria_check etc. After a normal shutdown one can copy Maria files between servers.

Advantages of Maria (Compared to MyISAM)

  • Data and indexes are crash safe. On crash, things will rollback to state of the start of statement or last LOCK TABLES commands.

  • Maria can replay everything from the log. Including CREATE/DROP/RENAME/TRUNCATE tables.

  • LOAD INDEX can skip index blocks for not wanted indexes

  • Supports all MyISAM row formats and the new transactional format where data is stored in pages.

  • When using transactional format (default) row data can be cached.

  • Maria has unit tests of most parts

  • Supports both crash safe (soon to be transactional) and not transactional tables. (Not transactional tables are not logged and rows uses less space.) CREATE TABLE foo (...) TRANSACTIONAL=0|1

  • Transactional is the only crashsafe/transactional row format.

  • Block format should give a notable speed improvement on systems with bad data caching (for example Windows).

Differences between Maria and MyISAM

  • Maria uses big (1GB by default) log files.

  • Maria has a log control file (maria_log_control) and log files ( maria_log.????????). The log files can be automatically purged when not needed or purged on demand (after backup).

  • Maria uses by default 8K pages for indexes (MyISAM 1K). Maria should be faster on static size indexes but slower on variable length keys (until we add a directory to index pages).

Disadvantages of Maria (compared to MyISAM), that will be fixed in forthcoming releases.

  • Maria 1.0 has one writer or many readers. (MyISAM can have one inserter and many readers when using concurrent inserts.)

  • Storage of very small rows (< 25 bytes) is not efficient for PAGE format.

  • In Maria PAGE format there is an overhead of 10 bytes/page and 5 bytes/row. Transaction and multiple concurrent writer support will use an additional overhead of 7 bytes for new rows, 14 bytes for deleted rows and 0 bytes for old compacted rows.

  • Maria doesn't support INSERT DELAYED.

  • The maria_page_buffer_size system variable that controls the Maria page cache size is not dynamically settable like the corresponding MyISAM variable, key_buffer_size.

Differences that are not likely to be fixed

  • No external locking (MyISAM has external locking, but it is not much used).

  • Maria has one page size for both index and data (defined when Maria is used first time). MyISAM supports different page sizes per index.

  • Index requires one extra byte per index page.

  • Maria doesn't support RAID (disabled in MyISAM too).

  • Minimum data file size for PAGE format is 16K (with 8K pages).