At least how many libraries are required for an important Myisam Mysql system?

For more important systems, the more the better, but there is always a minimum. It's like someone asking oracle rac how many nodes would be better. [@ more@]

The answer is three: main library, read library, and ready library.

Because of the management principle of Myisam locks, the query will block updates, and mysqlhotcopy will lock the table to prevent updates and queries. The availability of the system is greatly affected.

In this way, for systems that do read-write separation, in addition to writing and reading libraries, there must be a library for backup and report queries. Because report queries generally take a long time, it is impossible to allow the read library to be blocked for a long time, and as the database capacity increases, the backup time will become very long. Therefore, the role of the library is to alleviate these two parts, and another function of the library is to do replication. As we all know, when you do replication, you must lock all the tables, so reading the library obviously cannot be used as this role. And in critical systems, in order to prevent human error, delayed replication of MYSQL may be used. How to achieve delayed replication can be seen in my blog or google. Then the standby library can play this role at this time, so even if the conditions are again limited, there should be at least three libraries for highly available systems.