本节讨论如何执行 NDB 集群安装的 滚动重启，之所以称为滚动重启，是因为其涉及依次停止和启动（或重启）每个节点，从而使集群本身保持可运行状态。这通常作为 滚动升级 或 滚动降级 的一部分进行，其中集群的高可用性是强制性的，并且整个集群不允许停机。我们在提到升级时，这里提供的信息通常也适用于降级。This section discusses how to perform a rolling restart of an NDB Cluster installation, so called because it involves stopping and starting (or restarting) each node in turn, so that the cluster itself remains operational. This is often done as part of a rolling upgrade or rolling downgrade, where high availability of the cluster is mandatory and no downtime of the cluster as a whole is permissible. Where we refer to upgrades, the information provided here also generally applies to downgrades as well.

滚动重启可能有多种原因。接下来的几段将对此进行描述。There are a number of reasons why a rolling restart might be desirable. These are described in the next few paragraphs.

配置更改。 为更改集群的配置，例如向集群添加 SQL 节点，或将配置参数设置为新值。Configuration change.  To make a change in the cluster's configuration, such as adding an SQL node to the cluster, or setting a configuration parameter to a new value.

NDB 集群软件升级或降级。 将集群升级到较新的 NDB 集群软件版本（或降级到较旧的版本）。这通常被称为 “滚动升级”（或 “滚动降级”，当回退到较旧的 NDB 集群版本时）。NDB Cluster software upgrade or downgrade.  To upgrade the cluster to a newer version of the NDB Cluster software (or to downgrade it to an older version). This is usually referred to as a “rolling upgrade” (or “rolling downgrade”, when reverting to an older version of NDB Cluster).

节点主机更改。 对运行一个或多个 NDB 集群节点进程的硬件或操作系统进行更改。Change on node host.  To make changes in the hardware or operating system on which one or more NDB Cluster node processes are running.

系统重置（集群重置）。 重置集群，因为它已达到不良状态。在这种情况下，通常希望重新加载一个或多个数据节点的数据和元数据。这可以通过三种方式中的任何一种完成：System reset (cluster reset).  To reset the cluster because it has reached an undesirable state. In such cases it is often desirable to reload the data and metadata of one or more data nodes. This can be done in any of three ways:

资源回收。 释放之前通过连续的 INSERT 和 DELETE 操作分配给表的内存，以供其他 NDB Cluster 表重复使用。Resource Recovery.  To free memory previously allocated to a table by successive INSERT and DELETE operations, for re-use by other NDB Cluster tables.

执行滚动重启的过程可以概括如下：The process for performing a rolling restart may be generalized as follows:

NDB 集群支持升级节点时的顺序有一定灵活性。在升级 NDB 集群时，您可以在升级管理节点、数据节点或两者之前升级 API 节点（包括 SQL 节点）。换句话说，您可以按任意顺序升级 API 和 SQL 节点。但需遵守以下规定：NDB Cluster supports a somewhat flexible order for upgrading nodes. When upgrading an NDB Cluster, you may upgrade API nodes (including SQL nodes) before upgrading the management nodes, data nodes, or both. In other words, you are permitted to upgrade the API and SQL nodes in any order. This is subject to the following provisions:

在节点重启期间，任何 API 节点都无法执行模式操作（如数据定义语句）。部分由于这一限制，在在线升级或降级期间也不支持模式操作。此外，在升级或降级进行时，不可能执行本地备份。It is not possible for any API node to perform schema operations (such as data definition statements) during a node restart. Due in part to this limitation, schema operations are also not supported during an online upgrade or downgrade. In addition, it is not possible to perform native backups while an upgrade or downgrade is ongoing.

使用多个管理服务器进行滚动重启。 在对具有多个管理节点的 NDB 集群执行滚动重启时，您应记住，ndb_mgmd 会检查是否有其他管理节点正在运行，如果有，它会尝试使用该节点的配置数据。为了防止这种情况发生，并强制 ndb_mgmd 重新读取其配置文件，请执行以下步骤：Rolling restarts with multiple management servers.  When performing a rolling restart of an NDB Cluster with multiple management nodes, you should keep in mind that ndb_mgmd checks to see if any other management node is running, and, if so, tries to use that node's configuration data. To keep this from occurring, and to force ndb_mgmd to re-read its configuration file, perform the following steps:

在执行滚动重启以更新集群配置时，可以使用 ndbinfo.nodes 表的 config_generation 列来跟踪哪些数据节点已成功使用新配置重启。请参阅 第 25.6.15.48 节，“ndbinfo nodes 表”。When performing a rolling restart to update the cluster's configuration, you can use the config_generation column of the ndbinfo.nodes table to keep track of which data nodes have been successfully restarted with the new configuration. See Section 25.6.15.48, “The ndbinfo nodes Table”.