Restoring an NDB backup to a later version of the NDB Cluster

• When restoring the metadata from a backup (--restore-meta option), ndb_restore normally attempts to reproduce the captured table schema exactly as it was when the backup was taken.Tables created in versions of NDB prior to 8.0 use .frm files for their metadata. These files can be read by the mysqld in NDB 8.0, which can use the information contained therein to create the .sdi files used by the MySQL data dictionary in later versions.

frm file A file containing the metadata, such as the table definition, of a MySQL table. For backups, you must always keep the full set of .frm files along with the backup data to be able to restore tables that are altered or dropped after the backup. Although each InnoDB table has a .frm file, InnoDB maintains its own table metadata in the system tablespace; the .frm files are not needed for InnoDB to operate on InnoDB tables.

These files are backed up by the MySQL Enterprise Backup product. These files must not be modified by an ALTER TABLE operation while the backup is taking place, which is why backups that include non-InnoDB tables perform an FLUSH TABLES WITH READ LOCK operation to freeze such activity while backing up the .frm files. Restoring a backup can result in .frm files being created, changed, or removed to match the state of the database at the time of the backup. .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. Suspend An optional stage within the backup where the MySQL Enterprise Backup processing stops, to allow for user-specific operations to be run.

Read Blog: https://techqy.com/how-to-access-or-read-frm-file-explain-frm-file-in-mysql/

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writes) at the point where it is ready to install a new version of the table .frm file, discard the old file, and clear outdated table structures from the table and table definition caches.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. The sync_frm system variable has been removed because .frm files have become obsolete.

• Skip_open_table, Open_frm_only, Open_full_table (JSON property: message) These values indicate file-opening optimizations that apply to queries for INFORMATION_SCHEMA tables
  • Skip_open_table: Table files do not need to be opened. The information has already become available within the query by scanning the database directory.
  • Open_frm_only: Only the table's .frm file needs to be opened.
  • Open_full_table: The unoptimized information lookup. The .frm, .MYD, and .MYI files must be opened.
• File Name, Pattern, or Extension: .frm Relation to Original Data Files: Hold metadata about all MySQL tables. Note: The database is put into a read-only state while these files are copied. These files are copied unmodified. The extra metadata property for NDB tables are now used to store information from the MySQL data dictionary. Because this information is significantly larger than the binary representation previously stored here (a .frm file, no longer used), the hard-coded size limit for this extra metadata has been increased.

  • The sync_frm system variable. This variable will be removed when .frm files become obsolete.

  read other: https://techqy.com/what-is-frm-file-in-my-sql-and-how-to-access-an-frm-file/