This topic provides answers to frequently asked questions about the backup and restoration features of PolarDB for MySQL.
Data backup
Is the total physical size of level-1 backups (snapshots) equal to the sum of the logical sizes of level-1 backups (snapshots)?
No, the total physical size of level-1 backups of a cluster is the sum of the dedicated physical storage occupied by all level-1 backups, as shown in part ①. It is not the sum of the logical data sizes of all level-1 backups, as shown in part ②. 
Why is the total size of level-1 backups even smaller than the logical size of a single backup?
Level-1 backups in PolarDB are measured by two metrics: the logical size of the backups and their total physical storage. PolarDB uses snapshot chains to store level-1 backups. Only one record is generated for each data block. Therefore, the total physical storage of all level-1 backups is smaller than the total logical size of all level-1 backups. In some cases, the total physical storage of all level-1 backups is smaller than the logical size of a single backup.
How am I charged for backups in PolarDB?
You are charged for storage space of level-1, level-2, and log backups. By default, the level-1 backup and log backup features are enabled, and a free storage quota is provided. By default, the level-2 backup feature is disabled.
How are the fees of level-1 backups calculated?
The fee is calculated based on the following formula: Storage fee per hour = (Total size of level-1 backups - Used database storage space × 50%) × Unit price per hour. For example, assume that a cluster is deployed in a region within the Chinese mainland. The total size of level-1 backups of a PolarDB database is 700 GB, and the used database storage space is 1,000 GB. The storage fee per hour is calculated based on the following formula: (700 GB - 500 GB) × USD 0.000464/GB = USD 0.0928.
Can I use a storage plan to offset the storage fees of backups?
Yes, you can purchase a storage plan to offset the storage space used by all PolarDB clusters within your account. The remaining capacity of the storage plan is automatically used to offset the storage space that exceeds the free quota for level-1 backups at a ratio of 1:1.6 until the storage plan is exhausted. If the remaining capacity of the storage plan is insufficient to offset the storage space of level-1 backups, you are charged for the excess storage space on a pay-as-you-go basis. For more information, see FAQ about billing of storage plans.
How do I reduce the data volume and fees of level-1 backups, level -2 backups, and log backups?
Properly shorten the retention period of backup data. For more information, see Configure backup settings.
Shorten the retention period of Level-1 backup, for example, from seven days to three days.
Shorten the retention period of level-2 backup, for example, from 70 days to 30 days.
NoteShortening the retention period of level-1 and level-2 backup poses certain risks. If the backup set that you need to use to restore data is beyond this retention period, you cannot restore data.
Shorten the retention period of log backup, for example, from seven days to three days.
NoteShortening the retention period of log backups poses certain risks. If the backup set that you need to use to restore data is beyond this retention period, you cannot store data by point in time.
Reduce the backup frequency (backup cycle) appropriately. For more information, see Configure backup settings.
Reduce the frequency of level-1 backup, for example, from once a day to three times a week.
NoteDecreasing the frequency of level -1 backup may increase the time for restoring data by point in time.
Reduce the frequency of level-2 backup, for example, from three times per week to twice per week.
You can purchase storage plans to offset the fees of level-1 backup, level-2 backup, and log backup. For more information, see Storage plans.
Delete unneeded backup sets from the recycle bin of your cluster to lower the costs of level-2 backup. For more information, see Delete a released cluster.
Are level-1 backups the only ones that can be manually created?
Yes.
How long are manual backups retained?
The retention period of manual backups is specified by the value of the Level-1 Backup parameter in the Data Backup Retention section.
How do I view the size of a level-2 backup?
You can view the size of a level-2 backup on the Backups tab in the console.
How do I download backup sets to my computer?
For information about how to download backup sets, see Download backup files. The downloaded backup data sets cannot be used to directly restore the data to the PolarDB for MySQL cluster, but can be used to restore the data to a self-managed MySQL database. For more information, see Restore the data of a PolarDB cluster to a self-managed MySQL database by using snapshot backup files.
How do I archive backup files to OSS?
You can use one of the following methods to archive PolarDB for MySQL backup files to OSS:
Use DBS to store PolarDB for MySQL backup files to OSS. Perform the following steps:
Log on to the OSS console and create buckets. For information on how to create buckets, see Create buckets.
Configure a backup schedule. For more information, see Configure a backup schedule. After the backup is complete, you can manage backup sets. For example, you can query or download backup sets. For more information, see Query backup sets or Download backup sets.
Use mysqldump or Data Management (DMS) to export backup files, and then upload them to OSS. Perform the following steps:
Use mysqldump or DMS to export PolarDB for MySQL backup files.
Manually upload the exported backup files to OSS. For more information, see Upload objects.
Data restoration
Can I customize the names of restored databases or tables?
Yes.
If my cluster does not have a data backup, can I restore the data to a previous point in time?
No. To restore data to a previous point in time, you must restore the data of a full backup that was created before the specified point in time. Then, you need to restore the data generated after the backup that was created and before the specified point in time based on the redo logs.
Can I use the cross-region backup and restoration features for a cluster that has TDE enabled?
Yes.
Can I enable TDE for a cluster after cross-region restoration?
Yes.