Error 1001 ER_NISAMCHK is a legacy MyISAM check error that appears when the server or the isamchk utility detects table corruption or an unsupported internal call.
MySQL Error 1001 ER_NISAMCHK signals a legacy MyISAM table-check failure raised by the isamchk utility or an outdated server routine. Run REPAIR TABLE or isamchk –recover, convert the table to InnoDB, and upgrade MySQL to clear the error.
isamchk
Error 1001 appears when MySQL’s legacy MyISAM handler calls the isamchk routine or detects a corrupted .MYI/.MYD file. Although marked “Unused” in recent versions, the code may surface on older servers, during upgrades, or when low-level utilities run outside the server.
The error text is simply “isamchk,” referencing the standalone utility used to validate and repair MyISAM tables.
Modern MySQL defaults to InnoDB, so seeing this error often indicates that legacy tables or tools are still in use.
The error fires during query execution, server startup, or manual isamchk runs if MySQL finds structural issues in a MyISAM table header or key definition.
It can also pop up after abrupt shutdowns or disk issues that leave index files inconsistent.
Admins notice it in the error log, client session, or shell output while running maintenance scripts. Ignoring it risks data loss or read/write failures on the affected table.
Corrupted MyISAM tables can silently drop rows, mis-order indexes, and degrade performance.
Clearing Error 1001 quickly restores data integrity, stabilizes backups, and prepares the table for conversion to safer engines such as InnoDB.
.
Servers that were upgraded from MySQL 5.x may still host MyISAM tables. These tables rely on .MYI/.MYD files that are prone to corruption and trigger ER_NISAMCHK.
Crashes, power loss, or kill -9 signals interrupt writes and leave index pages half-flushed. The next start-up check surfaces Error 1001.
Bad sectors or full disks corrupt table headers.
isamchk detects the mismatch and returns the error code.
Running isamchk on an open MyISAM table without --force-close or stopping mysqld causes contention and unexpected error codes.
.
Prefer InnoDB for almost all workloads. MyISAM lacks crash recovery and row-level locking, increasing corruption risk.
No. Silent corruption may worsen. Run a repair and validate your backups immediately.
Severe corruption, insufficient disk space, or active connections can block repairs. Shut down mysqld and run isamchk –recover.
Galaxy’s editor surfaces server errors instantly, lets you run REPAIR TABLE with snippets, and endorses the fixed query for team reuse, reducing repeat incidents.
.avif)
.avif){kind=logo}
