2682120 - Error "Unknown database system" after upgrade

Warnings in SM21 as below after doing upgrade

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Details of database connection could not be read

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Checking further in workprocess trace, you can find similar error as below

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B Mon Aug 13 17:43:17:863 2018
B  *** ERROR => Unknown database system
 [dbcon.c      5950]
B  {root-id=D53DB4FE7ECD4DFA8B834AF497CD97EB}_{conn-id=00000000000000000000000000000000}_0
B  ***LOG BYA=> failed to read connection information for  from table DBCON [dbds         966]
B
B Mon Aug 13 17:43:19:408 2018
B  *** ERROR => Unknown database system

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Netweaver

DBCO,upgrade,database,unknown , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , BC-UPG-OCS , Online Corr. Support (Tools:Supp.-Pack., Addon Install/Upgr) , BC-DB-DBI , DB Independent Database Interface , Problem