HANA SDI – Oracle LogReader remote subscription exception

In my HANA Smart Data Integration environment I use few realtime replication based on Oracle Log Reader adapters. As the name of the adapter suggest the Oracle redo logs are required in this configuration.

The logs are used to retrieve the changed data from the source database.  Sometimes in adapater log You can find information like below. This information I received by email from HANA Alerts but the same information and more You can also find in Replication Agent log.

Alert "Remote Subscription exception" (id 710) on database SID of SID NR (hostname)
 snapshot   : 2021-05-19 08:35:32.0000000
 Alert Name : Remote Subscription exception
 Priority   : High
 Details    : Exception number 4708 in REMOTE SOURCE NAME. Affected REMOTE SUBSCRIPTIONS: remote.subscription,name::ORA_REPLICATION.SUB_VT_AP_FFF_DIM_PRAC: LogReader is in ERROR state [Locator <00000a65530589ea000000010000819300021dad00880a65530589e800000000> received from Data Provisioning Server is too old. No redo log file is available for log sequence number <33,171>.]. Check LogReader instance log .log for details.
 User Action: Investigate the error message and the error code and restart the remote subscription if necessary.

Therefore if you are getting this error message, the redo log with required information on the changed data no longer exists.  This happens frequently when an exception occurs during replication, and the exception is not resolved/cleared before the redo logs are archived.  SAP strongly recommends keeping redo logs for 72 hours before archiving or deleting.

Solution

Summary:

  • If the redo log has been archived, it is possible to restore the missing archive log and continue replication. 
  • If redo logs are not available, there is no way to resume replication.  The replication must be dropped and recreated.

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