The Physical Standby Database solution is an important part of the high availability capability of OceanBase Database. It ensures the high availability, data protection, and disaster recovery for your key applications.
What is Physical Standby Database?
The Physical Standby Database solution provides a quasi-real-time hot backup for the production database of OceanBase Database. When the primary database becomes unavailable as scheduled or unexpectedly, for example, a majority of replicas fail, the standby database takes over services and provides lossless and lossy disaster recovery to minimize service downtime and reduce possible data loss. In lossless disaster recovery, the recovery point objective (RPO) is 0. In lossy disaster recovery, the RPO is greater than 0.
In OceanBase Database earlier than V4.1.0, the Physical Standby Database solution is provided in the form of primary/standby clusters. Two cluster roles exist: primary cluster and standby cluster. All user tenants in the primary cluster are primary tenants, and all user tenants in a standby cluster are standby tenants. The standby cluster automatically synchronizes the tenant change operations performed in the primary cluster.
In OceanBase Database V4.1.0 and later, the Physical Standby Database solution is provided in the form of primary/standby tenants. Clusters are no longer assigned the primary or standby role and are only containers of primary and standby tenants. The primary tenant is a business tenant that supports complete database capabilities, including queries, data manipulation language (DML) operations, and data definition language (DDL) operations. A standby tenant only provides disaster recovery and read-only services. The tenant-level Physical Standby Database high availability solution comprises one primary tenant and multiple standby tenants.
Note
The Physical Standby Database solution of OceanBase Database is based on tenants. Therefore, in the product documentation of the current version of OceanBase Database, a primary database is equivalent to a primary tenant, and a standby database is equivalent to a standby tenant.
The Physical Standby Database solution transmits and stores logs by using the log transfer service and log storage service respectively, and ensures data consistency between the primary and standby tenants by using the log replay service.
The log transfer service synchronizes redo logs between the primary and standby tenants in real time.
The Physical Standby Database solution of OceanBase Database supports log synchronization only in asynchronous mode.
The log storage service provides highly available and reliable log storage and read/write capabilities.
Logs written by a standby tenant to the log storage service are applied by the log replay service to the MemStore in real time or with a delay. This ensures data consistency between the primary and standby tenants.
You can use the Physical Standby Database solution together with the multi-replica disaster recovery, arbitration-based disaster recovery, physical backup and recovery, and change data capture (CDC) features of OceanBase Database to meet your various data protection and availability requirements.
Deployment plan of the Physical Standby Database solution
The Physical Standby Database solution allows you to deploy one primary tenant and one or more standby tenants. The primary tenant provides read and write services for your business. The standby tenant synchronizes business data written in the primary tenant from redo logs in real time.
You can deploy a primary tenant and its standby tenants in multiple OceanBase clusters that are close to each other or far apart, or in the same OceanBase cluster. In other words, an OceanBase cluster can contain only primary tenants or standby tenants, or both. Tenant names, resource specifications, configurations, and locality settings of the primary and standby tenants can be different.
In addition, the primary and standby tenants can be single-replica tenants, multi-replica tenants, or tenants with arbitration-based high availability. Different deployment modes provide different levels of replica-based disaster recovery for tenants.
The tenant-based Physical Standby Database solution is highly flexible. You can deploy the solution in the following typical modes:
A cluster contains only primary or standby tenants
In this deployment mode, you deploy multiple OceanBase clusters, and each OceanBase cluster contains either primary or standby tenants.
This deployment mode allows you to use the Physical Standby Database solution for remote disaster recovery.
The following figure shows the architecture of this deployment mode.
A cluster contains both primary and standby tenants
In this deployment mode, you deploy multiple OceanBase clusters, and each cluster contains both primary and standby tenants or only primary tenants.
The following typical scenario is taken as an example:
Your business requires read/write and geo-disaster recovery in two different regions. Therefore, you must deploy both primary and standby databases in each region. In a database using other primary/standby solutions, you must deploy two or more clusters in each of the two regions, and clusters across regions work in primary/standby mode.
If you use OceanBase Database, you only need to deploy one cluster in each of the two regions, and deploy primary and standby tenants in the two clusters to meet your business requirements. This greatly simplifies management of database clusters. The following figure shows the architecture of this deployment mode.
Primary and standby tenants belong to one cluster
In this deployment mode, you deploy only one OceanBase cluster, and the primary tenant and one or more standby tenants belong to the same OceanBase cluster.
You can use this deployment mode in the following scenario:
Assume that you need to retain a database snapshot in a business tenant before a business upgrade. You can create a standby tenant for real-time synchronization in the same cluster of the business tenant and suspend the synchronization to the standby tenant before the business upgrade. Then, you can perform any read/write operations, for example, starting a business upgrade, in the primary tenant, without affecting the standby tenant. If the business upgrade fails, you can delete the primary tenant and set the standby tenant to a new primary tenant. You can change the name of the new primary tenant to that of the original primary tenant so that access to the proxy remains unchanged.
The following figure shows the architecture of this deployment mode.
