Backup to SFTP Server may fail due to connection limit
Details
| Detail name | Value |
|---|---|
| Changelog Number | 11459 |
| Type | Bug |
| Status | Open |
| Affected Versions | Exasol 6.2.0, Exasol 7.0.0, Exasol 7.1.0 |
Description
If the SFTP Server used for remote backups limits the amount of connections, backups may fail.
This happens because SFTP servers limit the amount of connections that were requested but not fully established yet. As Exasol opens multiple connections to the SFTP server at once, the backup can fail early if this limit is set too low.
Workaround
You can retry the backup.
For OpenSSH, the MaxStartups parameter should be increased. We recommend 4× the number of cluster nodes, as each database node can open multiple connections when a backup is started and Exaoperation might open additional ones to check the backup expiry status.
If the SFTP server is also used by other software, the limit should be raised accordingly or scheduling multiple backups or other processes there at the same timestamp should be avoided.
Fix
Backups retry the connection to the SFTP server in some common failure scenarios and stagger the connections to avoid a high peak in opened connections to the SFTP server.
