Explain the importance of checkpointing for backups

modules/ROOT/pages/backup-restore/online-backup.adoc

@@ -10,6 +10,24 @@ Remember to xref:backup-restore/planning.adoc[plan your backup] carefully and ba
 Note that it is not allowed to take a backup of a database alias, only physical databases can be backed up.
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+Before starting a backup, pay attention to your checkpointing policy, as the checkpoint has to be completed before the backup starts.
+
+Consider the following statements:
+
+* The backup cannot begin until the checkpoint finishes.
+
+* If the checkpoint takes longer than the configured backup timeout, this may cause the backup to fail.
+The configuration setting xref:configuration/configuration-settings.adoc#config_dbms.cluster.catchup.client_inactivity_timeout[`dbms.cluster.catchup.client_inactivity_timeout`] governs the backup timeout.
+
+* A subsequent backup attempt may succeed if the next checkpoint takes less time.
+
+* Taking a backup during traffic may fail, as checkpoints during high traffic may take much longer than usual.
+
+* If checkpoints take consistently long to finish and backup timeouts cannot be pressed back far enough to be practical, you need to tune up checkpoint frequency, IOs, or even disk IOs.
+
+
+To configure the checkpointing policy, see xref:database-internals/checkpointing.adoc[Database internals -> Checkpointing and log pruning].
+
 [[online-backup-command]]
 == Command