The full-featured replica or read-only replica of each partition in a standby cluster replays REDO logs in real time and hosts the read service. OceanBase Database provides intra-partition and inter-partition consistency reads and generates each read result in the form of a snapshot to ensure transaction consistency.
The replay progress varies by partition or replica. Therefore, the data read later may be older than the previously read data in default configurations. To resolve this issue, OceanBase Database allows you to specify whether to enable monotonic read. After monotonic read is enabled, tenant-specific monotonically increasing version numbers of readable data are maintained. In each read operation, the globally up-to-date readable data is obtained as a snapshot. This ensures that the data read later is newer than the previously read data.
OceanBase Database supports bounded staleness consistency reads to ensure that the read data is out-of-sync with the latest data of the primary cluster by less than a specific period of time. The default period is 5s. If data in a standby cluster is out-of-sync with the latest data of the primary cluster by a period of time exceeding the specified threshold, the read operation is retried and waits until timeout, or until the data in the standby cluster is updated based on the latest data of the primary cluster.
For more information, see Weak consistency read.