tailieunhanh - MySQL High Availability- P12

MySQL High Availability- P12: A lot of research has been done on replication, but most of the resulting concepts are never put into production. In contrast, MySQL replication is widely deployed but has never been adequately explained. This book changes that. Things are explained here that were previously limited to people willing to read a lot of source code and spend a lot of time debugging it in production, including a few late-night sessions. | However is it is possible to use the NDB Cluster technologies without the MySQL server but this requires lower-level programming with the NDB API. The NDB API is object-oriented and implements indexes scans transactions and event handling. This allows you to write applications that retrieve store and manipulate data in the cluster. The NDB API also provides object-oriented error-handling facilities to allow orderly shutdown or recovery during failures. If you are a developer and want to learn more about the NDB API see the MySQL NDB API online documentation. How Does MySQL Cluster Differ from MySQL You may be wondering What is the difference between a cluster and replication There are several definitions of clustering but it can generally be viewed as something that has membership messaging redundancy and automatic failover capabilities. Replication in contrast is simply a way to send messages data from one server to another. We discuss replication within a cluster also called local replication and MySQL replication in more detail later in this chapter. Typical Configuration You can view the MySQL Cluster as having three layers Applications that communicate with the MySQL server The MySQL server that processes the SQL commands and communicates to the NDB storage engine The NDB Cluster components sometimes called data nodes that process the queries and return the results to the MySQL server You can scale up each layer independently with more server processes to increase performance. Figure 15-1 shows a conceptual drawing of a typical cluster installation. The applications connect to the MySQL server which accesses the NDB Cluster components via the storage engine layer specifically the NDB storage engine . We will discuss the NDB Cluster components in more detail momentarily. There are many possible configurations. You can use multiple MySQL servers to connect to a single NDB Cluster and even connect multiple NDB Clusters via MySQL replication. We will discuss more