Backing up and restoring

Backups

Cloud Service provides two methods of backups:

• Cloud Service backs up the data in your PostgreSQL clusters using Barman. You can change the retention period on the Backups tab when you create or edit your cluster. Depending on the cloud your cluster is deployed on, Cloud Service uses either of the following cloud object storage solutions.

  Cloud	Object storage solution
  AWS	Amazon S3 (standard tier)
  Azure	Azure Blob Storage (in the "hot" access tier with geo-zone-redundant storage (GZRS))
  Google Cloud	Cloud Storage

  Your organization is responsible for the charges associated with the cloud object storage solution.

  You can change the retention period on the Additional Settings tab when you create or edit your cluster.

• Volume snapshots are the snapshot backups stored on disk in the same region as your cluster. Volume snapshots represent a snapshot of a volume on a storage system. Volume snapshots are very fast as compared to the backups using Barman. You can opt for volume snapshots from Additional Settings tab while creating and editing a cluster. Once you enable the volume snapshots, it captures the snapshot of a volume.

  Volume snapshots are:

  • stored on the disk in the same region as the cluster. It may increase the storage costs as per your cloud service providers.
  • supported on all the cluster types — single-node, high-availability clusters, and distributed high-availability clusters
  • supported for both the environments — EDB Hosted Cloud Service and Your Own Account
  • retained for 30 days
  • restored to the same region as your cluster

PostgreSQL clusters in Cloud Service are continuously backed up through a combination of base backups (backups using Barman and volume snapshots if enabled) and transaction log (WAL) archiving. When a new cluster is created, an initial "base" backup and a volume snapshot is taken. After that, every time a WAL file is closed, which is, by default, up to every 5 minutes, it's uploaded to the cloud object storage solution. If your cluster has faraway replicas, Cloud Service copies the WAL files from your cloud object storage solution and asynchronously transfers them to the faraway replicas. Your organization is responsible for the charges associated with the cloud object storage solution.

Replication lag with faraway replicas

With faraway replicas, the primary server writes to the archive, which is moved to the object store. The replica reads from the object store as files arrive. Prior to the archive replicating across to the replica, the log file must write at least 16MB (the WAL segment size) of data to the WAL to cut a new archive file. If the time interval for closing a WAL file is too large, it can introduce a delay until the replica receives the latest record. The amount of time that it takes to fill up the 16MB log file and copy it to the archive is the replication lag. The replication lag is the period of time when data can be lost. It can be minutes or hours, depending on the amount of activity in your database. You need to measure the replication lag to determine if it's acceptable from a possible data-loss perspective. If it isn't acceptable, consider using a distributed high-availability cluster.

To determine the replication lag, you can compare the last log sequence number (LSN) in the 16MB log file on the primary to the LSN in the log file in the replica.

Restores

If a restore is necessary—for example, in case of an accidental DROP TABLE statement—you can restore clusters to any point in the backup retention period.

Cluster restores aren't performed in place on an existing cluster. Instead, a new cluster is created and initialized with data from the backup archive. Restores must replay the transaction logs between the most recent full database backup and the target restore point. Thus restore times (that is, RTO) depend on the write activity in the source cluster.

By default, Cloud Service retains backups for 30 days for both types of backups.

You can restore base backups into a new cluster in any region supported by Cloud Service. However, you can restore the volume snapshots into a new cluster only in the same region.

Perform a cluster restore

The restore operation is available for any cluster that has at least one available backup. For newly created clusters, the initial backup becomes available a few minutes after the new cluster is fully operational.

Restore a single-node or primary/standby high-availability cluster

1. Select the cluster you want to restore on the Clusters page in the Console.
2. From Quick Actions, select Restore.
3. On the Restore Cluster page:
   1. Fill in the required fields.
   2. In the Cluster settings tab, go to the Source section.
   3. To restore to the last possible recovery point, in the Point in Time Restore field, select Now. Or, to restore further back in time, choose a timestamp.
   4. Review your selections in Cluster Summary and select Restore Cluster to begin the restore process.
      • If you opted for volume snapshots and you're restoring the cluster in the same region as your source cluster, Cloud Service chooses volume snapshots for restoration over Barman object store backups.
      • If you opted for volume snapshots and you're restoring the cluster in a different region from your source cluster, Cloud Service chooses the Barman object store backup for restoration over volume snapshots.
4. The new cluster is now available on the Clusters page.

Restore a distributed high-availability cluster

1. On the Clusters page in the Console, select the cluster you want to restore.
2. Select Quick Actions > Restore.
3. In the Cluster Settings tab, enter a cluster name and password for your restored cluster.
4. Select Next: Data Group.
5. Select the Node Settings tab.
6. In the Source section, select Fully Restore or Point in Time Restore. A point-in-time restore restores the data group as it was at the specified date and time.
7. In the Nodes section, select Two Data Nodes or Three Data Nodes. For more information on node architecture, see Distributed high availability.
8. Follow the steps for Creating a distributed high-availability cluster.
9. Select Restore.
   • If you opted for volume snapshots and you're restoring the cluster in the same region as your source cluster, then Cloud Service chooses volume snapshots for restore over base backups.
   • If you opted for valume snapshates and you're restoring the cluster in the different region from your source cluster, then Cloud Service chooses the base backup for restore over volume snapshots.
10. The new cluster is now available on the Clusters page.