The Secret Of Read.FRM file
Read .frm file format
The format used by InnoDB for its data files named ibdata1, ibdata2, and so on. Each file format supports one or more row formats.
A full backup consists of a hot backup phase that copies the InnoDB data, followed by a warm backup phase that copies any non-InnoDB data such as MyISAM tables and .frm files.
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An optional stage within the backup where the MySQL Enterprise Backup processing stops, to allow for user-specific operations to be run. The mysqlbackup command has options that let you specify commands to be run while the backup is suspended. Most often used in conjunction with backups of InnoDB tables only, where you might do your own scripting for handling .frm files.
The exception referred to earlier is that ALTER TABLE block reads (not just writes) at the point where it is ready to install a new version of the table .frm file, discard the old file, and clear outdated table structures from the table and table definition caches. At this point, it must acquire an exclusive lock. To do so, it waits for current readers to finish, and blocks new reads and writes.