Что такое формат файла MYD?
A .myd file is the row-data component of a MySQL MyISAM table. MyISAM stores each table as three sibling files sharing the same base name: table.frm holds the schema definition, table.MYD holds this file - the actual row records - and table.MYI holds the indexes and engine metadata.
The .myd file contains only raw binary row data with no column definitions of its own. It cannot be read in isolation; the .frm definition file and a running MySQL or MariaDB server are required to interpret the records. Rows are stored in one of three internal layouts: FIXED (all columns fixed-width), DYNAMIC (default when VARCHAR or BLOB columns are present), or COMPRESSED (read-only tables packed offline with myisampack).
By default the file size is capped at 4 GB, but this can be raised to up to 256 TB by setting MAX_ROWS and AVG_ROW_LENGTH table options. Deleted rows are not immediately reclaimed - they remain as gaps on a free list until OPTIMIZE TABLE is run. An optional live checksum (CHECKSUM=1) lets the engine track row-level integrity; the myisamchk utility and CHECK TABLE / REPAIR TABLE SQL statements work against the companion .MYI to diagnose and repair corruption.
MyISAM was the default MySQL storage engine from MySQL 3.23 (circa 2001) until MySQL 5.5 (2010), when InnoDB became the new default. Legacy databases and read-mostly workloads still produce .myd files today, supported by both MySQL and MariaDB.
Безопасность и защита
РИСК: MEDIUMA .MYD is inert data - it contains no executable code - but it carries the same operational and privacy risks as any database file. Operationally: never copy, move, or delete .MYD files while the MySQL server is running, and never separate a .MYD from its matching .frm and .MYI or mix files across incompatible server versions - doing so corrupts or "crashes" the table. Privacy-wise the .MYD holds the table's actual rows in plaintext on disk (MyISAM has no encryption), so a leaked .MYD is a data breach exposing whatever the table stored - user records, e-mails, PII. Always work on copies and treat it like the sensitive database it is.
Детали формата
в двух словахПрограммы, открывающие файлы MYD
Windows4 apps
MySQL Workbench
Открытый код GUI client - connect to a running MySQL server that already has the table loaded, then browse and export. It cannot read a raw .MYD by itself. 
MySQL Server
Открытый код The proper route: copy the .frm + .MYD + .MYI trio into the server's data directory (matching version), start MySQL, then SHOW CREATE TABLE / mysqldump to read or export the rows.
MariaDB Server
Открытый код MariaDB fully supports MyISAM - drop the three files into its data dir and dump the data. Often the easiest target for very old tables.
myisamchk (bundled with MySQL/MariaDB)
Открытый код Offline check/repair of a crashed table: 'myisamchk -r tablename.MYI' (works on the .MYD/.MYI pair while the server is stopped). 
macOS1 app
MySQL Server / MariaDB
Открытый код Same approach as Windows: restore the .frm/.MYD/.MYI trio into a matching server and dump the table. No standalone .MYD viewer exists. 
Linux2 apps
MySQL / MariaDB Server
Открытый код Copy the three files into /var/lib/mysql/<db>/ (matching version), start the service, then SHOW CREATE TABLE / mysqldump. The standard server-side route.
myisamchk (bundled)
Открытый код Repair a damaged MyISAM table offline: 'myisamchk --recover table.MYI'. Stop the server first and work on a copy. Технические подробности
глубокая спецификация| File role | Stores raw row data for one MyISAM table; contains no schema, indexes, or engine metadata |
| Companion files | Always paired with `table.frm` (schema) and `table.MYI` (indexes) in the MySQL data directory; the three files share the same base name |
| Row format | FIXED (fixed-width columns), DYNAMIC (variable-length; default when VARCHAR or BLOB columns are present), or COMPRESSED (read-only, packed with myisampack) |
| Byte order | Little-endian |
| Encoding | Binary - raw binary record heap, no text encoding |
| File signature | No fixed magic bytes or printable ASCII signature; identified by extension and the presence of sibling .frm and .MYI files |
| Default file size limit | 4 GB per table data file |
| Maximum file size | Up to 256 TB, configured via MAX_ROWS and AVG_ROW_LENGTH table options at table creation |
| Deleted row handling | Deleted rows leave gaps on an internal free list; space is reclaimed by running OPTIMIZE TABLE |
| Compression | None by default; read-only tables can be packed offline with myisampack to produce a compressed, read-only variant |
| Encryption | No native table-level encryption - a known MyISAM limitation compared with InnoDB |
| Checksum and integrity | Optional live checksum enabled with CHECKSUM=1 table option; integrity repair via myisamchk, CHECK TABLE, or REPAIR TABLE |
| MIME type | application/octet-stream |
| Platform support | Cross-platform: Linux, Windows, macOS, FreeBSD - anywhere MySQL or MariaDB runs |
| Superseded by | InnoDB .ibd files for transactional workloads; InnoDB became the MySQL default storage engine in MySQL 5.5 (2010) |
| Выпущен | 2001 (MyISAM became the default MySQL engine in MySQL 3.23) |
| Последняя версия | Still produced by any MySQL/MariaDB table using ENGINE=MyISAM (legacy default before InnoDB took over in MySQL 5.5, 2010) |
| Спецификация | dev.mysql.com |
Конвертации MYD
Вопросы и ответы сообщества
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