MySQL 5.7 Release Notes
If you have started mysqld with the
myisam_recover_options system
variable set, MySQL automatically checks and tries to repair
MyISAM tables if they are marked as 'not
closed properly' or 'crashed'. If this happens, MySQL writes
an entry in the hostname.err file
'Warning: Checking table ...' which is
followed by Warning: Repairing table if the
table needs to be repaired. If you get a lot of these errors,
without mysqld having died unexpectedly
just before, then something is wrong and needs to be
investigated further.
When the server detects MyISAM table
corruption, it writes additional information to the error log,
such as the name and line number of the source file, and the
list of threads accessing the table. Example: Got an
error from thread_id=1, mi_dynrec.c:368. This is
useful information to include in bug reports.
See also Section 5.1.6, “Server Command Options”, and Section 5.8.1.7, “Making a Test Case If You Experience Table Corruption”.