PolarDB:Backup and restoration

Data backup

Data backup varies based on the storage type.

• Storage type: Standard Edition Enterprise SSD (ESSD).

  Backup feature	Enabled by default	Retention period	Description	How to view backup size
  Data backup	Yes	3 to 7300 days	Data backup uses snapshots to capture and store data across the distributed storage system of the cluster. This method allows you to quickly back up and restore data. However, data backups (snapshots) can consume significant storage resources, which potentially drives up costs. If you retain data backups for an extended period of time, the write performance of the cluster may be degraded. We recommend that you retain data backups for no more than two weeks. A free quota of storage space is provided for data backups. You may be charged additional fees for excess storage usage. You can modify the backup schedule to manage the size of the data backups.	The physical size of data backups is shown in the following figure. Note Data Backup Physical Size (callout 1 in the figure) of a PolarDB cluster: the total amount of physical storage space that all data backups occupy. The data of the PolarDB cluster and the data backups use the same data blocks in the storage system. You are charged based on data blocks. Backup Set Logical Size (callout 2 in the figure) of a PolarDB cluster: the logical data size of a backup set (also called backup or snapshot). You are charged for data backups based on the occupied physical storage space instead of the logical data size. The physical storage space occupied by a data backup starts at 0 and increases as more data is written into the backup but does not exceed the data size.

Physical log backup

• Benefits

  The log backup feature allows you to create backups by uploading real-time redo logs to Object Storage Service (OSS) in parallel. The feature is enabled by default, and log backups are retained for 3 to 7,300 days. You can permanently save log backups by enabling the Permanently Retain Backups before Cluster Deletion feature.

  Note

  By default, the log backup feature is enabled, and you cannot disable this feature.

  Based on a full backup set and the log backups generated after the backup set is created, you can perform point-in-time recovery for a PolarDB cluster. This prevents data loss and ensures data security. If you perform PITR, you must consider the amount of time that is required to query redo logs, which is affected by the amount and workload of your business data. In most cases, redo logs are queried at a rate of 1 GB every 20 seconds to 180 seconds. The total restoration duration is the sum of the time required to restore backup sets and the time required to query redo logs.

• View backup size

  The following figure shows the total size of log backups.

  

Intra-region backup and cross-region backup

• Differences

  Backup type	Description	Enabled by default	Scenario	Benefits
  Intra-region backup	Backup files are stored across different zones in the same region.	Yes Note By default, this storage method is enabled when you enable level-2 backup.	Long-term archiving	Allows you to reduce costs by dumping data at a low backup frequency.
  Cross-region backup feature	Backup files are stored across regions.	Disabled. You must manually enable cross-region backup.	Geo-redundancy and MLPS level 3	Allows you to reduce recovery point objective (RPO). This backup storage method is suitable for private network environments that are encrypted and highly secure. You can reduce costs by dumping data at a low backup frequency.

  Note

  Low-frequency level-2 backup: The backup frequency of level-2 backup is lower than that of level-1 backup.

• Alibaba Cloud regions in which the cross-region backup feature is supported

  Source region	Destination region
  China (Hangzhou), China (Shanghai), China (Qingdao), China (Beijing), China (Shenzhen), and China (Hong Kong).	China (Hangzhou), China (Shanghai), China (Qingdao), China (Beijing), China (Shenzhen), and China (Hong Kong). Note Cross-region backup files are replicated to a region that is different from the source region.
  US (Virginia)	US (Silicon Valley)

Backup data protection

• Tamper-proofing:

  • Data backups of PolarDB for PostgreSQL are classified by storage location: level-1 backups are snapshots in PolarDB distributed storage, and level-2 and log backups reside in OSS. Both support Write Once Read Many (WORM) to prevent tampering.

    Note

    Standard Edition clusters support only level-1 backup (data backup), not level-2 backup.

• Malicious or accidental deletion prevention:

  • Manual deletion: You can delete only manual backups, not automatic backups.

  • Automatic deletion upon expiration: Automatic backups are deleted when the retention period expires and cannot be disabled. The minimum retention period in backup policy settings is 3 days (default: 7 days), with backups running at least twice a week. Therefore, automatic full backup and log backup data cannot be completely deleted.

Pricing

You can use the backup and restoration feature free of charge. However, backup files consume storage space. For information about the billing rules for the backup storage space, see Billing rules for backup storage that exceeds the free quota for Standard Edition clusters or .