Merge storage engine

Normally used storage engines:

Inno DB
CSV
Merge
Blackhole
Federated
eBay Memory Engine
Maria
PBXT
MySQL storage engines
NitroEDB
XtraDB
eBay Memory Engine
Solid

Merge Storage engine:
The Merge storage engine is effectively a view over MyISAM tables. This engine was originally designed to overcome operating system limitations when file systems could not support individual
files greater than 2G.
With Merge you can select data from multiple identical defined tables. You can then update and
delete data appropriately. Inserts occur on the last specified table in the merge definition. While you
can perform DML and SELECT statements on the Merge table, you can also perform these on the
underlying MyISAM tables. Primary key and unique key constraints are also on a per-table basis, not
on the Merge table.

 

parameters of Merge

understanding the properties and parameters of Merge, refer to MyISAM. Though this may appear to be similar to partitioning, there is no intelligence with Merge. Queries are executed against underlying
tables serially.
Merge can be successfully used when you want to manage manual partitioning and improved locking
strategy with MyISAM.

Using myisam-recover=FORCE,BACKUP with Merge. There have been many reported problems in this area.

Design of merge table :

A Merge table is represented by the individual files for each underlying MyISAM table and two additional
 tables in the file system located in the defined data directory for the MySQL instance.
table.frm: This is the Merge table format definition file.
table.MRG: This is the Merge table meta data of underlying tables.

Storage engines