Teradata 简明教程
Teradata - Data Protection
本章介绍了 Teradata 中提供的用于数据保护的功能。
This chapter discusses the features available for data protection in Teradata.
Transient Journal
Teradata 使用临时日志来防止事务失败导致的数据丢失。每当运行任何事务时，临时日志都会保留受影响行的映像副本，直到事务成功或成功回滚为止。然后，将丢弃之前的映像。临时日志保存在每个 AMP 中。这是一个自动过程，并且无法禁用。
Teradata uses Transient Journal to protect data from transaction failures. Whenever any transactions are run, Transient journal keeps a copy of the before images of the affected rows until the transaction is successful or rolled back successfully. Then, the before images are discarded. Transient journal is kept in each AMPs. It is an automatic process and cannot be disabled.
Fallback
备用保护通过在另一个称为备用 AMP 的 AMP 上存储表的第二行副本来保护表数据。如果一个 AMP 发生故障，则可以访问备用行。这样，即使一个 AMP 发生故障，数据仍然可以通过备用 AMP 获得。备用选项可以在创建表时或创建表后使用。备用可确保始终将表行的第二副本存储在另一个 AMP 中，以防止 AMP 故障导致数据丢失。但是，备用占据了插入/删除/更新操作的两倍存储空间和 I/O。
Fallback protects the table data by storing the second copy of rows of a table on another AMP called as Fallback AMP. If one AMP fails, then the fallback rows are accessed. With this, even if one AMP fails, data is still available through fallback AMP. Fallback option can be used at table creation or after table creation. Fallback ensures that the second copy of the rows of the table is always stored in another AMP to protect the data from AMP failure. However, fallback occupies twice the storage and I/O for Insert/Delete/Update.
以下图表显示了如何将行的备用副本存储在另一个 AMP 中。
Following diagram shows how fallback copy of the rows are stored in another AMP.
Down AMP Recovery Journal
当 AMP 发生故障并且表受到备用保护时，会激活 Down AMP 恢复日志。此日志会跟踪对发生故障的 AMP 的数据的所有更改。日志会在集群中剩余的 AMP 上激活。这是一个自动过程，并且无法禁用。当有故障的 AMP 恢复后，Down AMP 恢复日志中的数据将与 AMP 同步。完成此操作后，将丢弃日志。
The Down AMP recovery journal is activated when the AMP fails and the table is fallback protected. This journal keeps track of all the changes to the data of the failed AMP. The journal is activated on the remaining AMPs in the cluster. It is an automatic process and cannot be disabled. Once the failed AMP is live then the data from the Down AMP recovery journal is synchronized with the AMP. Once this is done, the journal is discarded.
Cliques
隔离是一种机制，Teradata 使用它来保护数据免遭节点故障的影响。隔离只不过是一组共享一组公共磁盘阵列的 Teradata 节点。当一个节点发生故障时，有故障节点的 vproc 将迁移到隔离中的其他节点，并继续访问其磁盘阵列。
Clique is a mechanism used by Teradata to protect data from Node failures. A clique is nothing but a set of Teradata nodes that share a common set of Disk Arrays. When a node fails, then the vprocs from the failed node will migrate to other nodes in the clique and continue to access their disk arrays.
Hot Standby Node
热备用节点是不参与生产环境的节点。如果一个节点发生故障，则有故障节点的 vproc 将迁移到热备用节点。一旦恢复发生故障的节点，它将成为热备用节点。热备用节点用于在发生节点故障时维持性能。
Hot Standby Node is a node that does not participate in the production environment. If a node fails then the vprocs from the failed nodes will migrate to the hot standby node. Once the failed node is recovered it becomes the hot standby node. Hot Standby nodes are used to maintain the performance in case of node failures.
RAID
独立磁盘冗余阵列 (RAID) 是一种用于保护数据免受磁盘故障影响的机制。磁盘阵列由一组磁盘组成，这些磁盘被分组为一个逻辑单元。此单元在用户看来可能像一个单元，但可能分布在多个磁盘上。
Redundant Array of Independent Disks (RAID) is a mechanism used to protect data from Disk Failures. Disk Array consists of a set of disks which are grouped as a logical unit. This unit may look like a single unit to the user but they may be spread across several disks.
RAID 1 通常在 Teradata 中使用。在 RAID 1 中，每个磁盘都与一个镜像磁盘关联。对主磁盘中的数据的任何更改也会反映在镜像副本中。如果主磁盘发生故障，则可以访问镜像磁盘中的数据。
RAID 1 is commonly used in Teradata. In RAID 1, each disk is associated with a mirror disk. Any changes to the data in primary disk is reflected in mirror copy also. If the primary disk fails, then the data from mirror disk can be accessed.
