Answers to frequently asked questions about backup and restoration in PolarDB for PostgreSQL (Compatible with Oracle).
Data backup FAQ
Is the total size of level-1 backups equal to the sum of the sizes of all individual level-1 backups?
No. The total size of level-1 backups — shown in part ① of the following figure — is smaller than the sum of the sizes of all individual backups.
PolarDB uses snapshot chains to store level-1 backups. Each data block is recorded only once across all snapshots, so the total physical storage is smaller than the total logical size. In some cases, the total physical storage is even smaller than the logical size of a single backup.
How are level-1 backup storage fees calculated?
Storage fees are charged hourly based on the amount of level-1 backup storage that exceeds the free quota:
Storage fee per hour = (Total size of level-1 backups − Used database storage space × 50%) × Price per hour[700 GB - 500 GB] × USD 0.000464 = USD 0.0928
The free quota equals 50% of your used database storage space. Storage beyond that quota is billed at the hourly rate.
Example (region within the Chinese mainland, price: USD 0.000464/GB/hour):
| Scenario | Total backup size | Used storage | Free quota | Billed size | Hourly fee |
|---|---|---|---|---|---|
| Backup exceeds free quota | 700 GB | 1,000 GB | 500 GB | 200 GB | USD 0.0928 |
Which backup types incur storage fees?
Level-1 backups, level-2 backups, and log backups all incur storage fees. Level-1 backups and log backups are enabled by default and include a free storage quota. Level-2 backups are disabled by default.
Can I use a storage plan to offset backup storage fees?
Yes. A storage plan offsets storage space used by all PolarDB clusters in your account. The remaining capacity of the storage plan is automatically applied against level-1 backup storage that exceeds the free quota, at a ratio of 1:1.6.
If the storage plan capacity runs out, additional backup storage is billed on a pay-as-you-go basis. For more information, see .
Can I create manual backups for level-2 backups or log backups?
No. Only level-1 backups can be created manually.
How long are manually created backups retained?
The retention period for manually created backups is set by the Level-1 Backup parameter in the Data Backup Retention Period section.
Where can I view the size of a level-2 backup?
The size of a level-2 backup is available on the Backups tab in the console.
Data restoration FAQ
How do I restore data that was accidentally deleted or modified?
Choose a restoration method based on your scenario:
Point-in-time recovery: Restore data to any point in time within the retention period. For details, see Restoration method 1: Restore data to a specific point in time.
Backup set restore: Restore data from a specific snapshot. For details, see Restoration method 2: Restore data from a backup set (snapshot).
Can I customize the names of restored tables?
Yes.
Can I restore data to a point in time if no backup exists before that point?
No. Point-in-time recovery requires a full backup created before the target point in time. PolarDB restores that full backup first, then replays the physical logs generated between the backup time and the target time to bring data to the exact point you specified.