We observed throttling and finally message flow within BizTalk completely stopped. When we checked SQL Server event log, we saw the following error:
The following stored procedure call failed: ” { call [dbo].[bts_UpdateMsgbox_BizTalkServerApplication_64]( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)}”. SQL Server returned error string: “Transaction (Process ID 67) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.;Duplicate key was ignored.”.