MySQL集群核心概念

MySQL Cluster Core Concepts

(also known as ) is an in-memory storage engine offering high-availability and data-persistence features.

NDBCLUSTER(也叫做NDB)是一种提供了高可用性和数据持久性特征的内存式存储引擎。

The storage engine can be configured with a range of failover and load-balancing options, but it is easiest to start with the storage engine at the cluster level. MySQL Cluster‘s storage engine contains a complete set of data, dependent only on other data within the cluster itself.

NDBCLUSTER存储引擎能够配置一系列的故障切换和负载均衡功能，然而它也是在集群级别下最容易入手的存储引擎。MySQL集群的NDB存储引擎包含一套完整的数据集，它仅依赖于在集群本身中的其他数据。

The “Cluster” portion of MySQL Cluster is configured independently of the MySQL servers. In a MySQL Cluster, each part of the cluster is considered to be a node.

MySQL集群的Cluster部分是独立配置在MySQL服务上面的。在MySQL集群中，集群的每个部分都被看做是一个节点（node）。

注意：

一般情况下，充分的去保存和检查集群日志是很有必要的。而节点日志则仅仅是作为开发和调试目的去检查的。

Checkpoint.  Generally speaking, when data is saved to disk, it is said that a checkpoint has been reached. More specific to MySQL Cluster, a checkpoint is a point in time where all committed transactions are stored on disk. With regard to the storage engine, there are two types of checkpoints which work together to ensure that a consistent view of the cluster‘s data is maintained. These are shown in the following list:

检查点：一般而言，当数据存到硬盘上时，Checkpoint就已经存在了。对于MySQL集群更明确的讲，一个检查点就是一个存储在硬盘上及时提交事务的点。对于NDB存储引擎来讲，这两种类型的检查点是一起工作的，并确保了集群数据的一致性视图是可维护的。这些会显示在以下列表中：

Local Checkpoint (LCP): This is a checkpoint that is specific to a single node; however, LCPs take place for all nodes in the cluster more or less concurrently. An LCP involves saving all of a node‘s data to disk, and so usually occurs every few minutes. The precise interval varies, and depends upon the amount of data stored by the node, the level of cluster activity, and other factors.

l  本地检查点（LCP）：对于一个单一的节点来说，这是一个特殊的检查点。然而，LCPs在集群的所有节点中或多或少是同时发生的。一个LCP在硬盘上涉及到了所保留的所有数据节点，因此在通常每隔几分钟都会发生。精确的时间间距各不相同，并且需要通过节点依赖于大量所存储的数据，集群的级别是活跃的，或者其他因素。

Global Checkpoint (GCP): A GCP occurs every few seconds, when transactions for all nodes are synchronized and the redo-log is flushed to disk.

l  全局检查点（GCP）：一个GCP每隔几秒就会发生一次，此时所有节点的事务是同步的，并且重写的日志会刷新到硬盘上。

For more information about the files and directories created by local checkpoints and global checkpoints, see .

关于通过本地检查点和全局检查点创建的文件和目录的更多信息，请见

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