3743620 - Rep Agent is slow due to waiting for writing the DBINFO - SAP ASE HADR

1. In HADR environment, Rep Agent is very slow and that caused ASE transaction log backlog (MB) keeps increasing in 'sap_status resource' output, as a result, primary ASE transaction log can not be truncated and HADR has to be disabled over and over again when log space is full.

2. Based on the collected information following KBA below

3171196 - How to collect information on performance with HADR 'Always On' - SRS 

Multiple times of "select * from master..monProcessWaits" shows the event with the highest waiting time is WaitEventID=31 "waiting for buf write to complete before writing".
The only write operation performed by Rep Agent Scanner is the writing of the DBINFO to disk.

Here is a sample:

select * from master..monProcessWaits where SPID in (select ScannerSPID from master..monRepScanners where DBName='<SID>')

 SPID        InstanceID KPID        ServerUserID OrigServerUserID WaitEventID Waits       WaitTime   
 ----------- ---------- ----------- ------------ ---------------- ----------- ----------- -----------
         426          0  1764164700            0                0          29       81397      154090
         426          0  1764164700            0                0          31    32804078    35526131
         426          0  1764164700            0                0          36         104         185
         426          0  1764164700            0                0         124    36228444    24718714
         426          0  1764164700            0                0         150       12744       12896
         426          0  1764164700            0                0         214        2004          33
         426          0  1764164700            0                0         215    69155949      845197
         426          0  1764164700            0                0         686           1        2016
         426          0  1764164700            0                0         876          10           0    
         426          0  1764164700            0                0         908       29172     4516256 

And this is confirmed by the stack traces collected for Rep Agent Scanner which shows the functions buf__writewait and dbinforelease.

SAP Adaptive Server Enterprise with Always-on 16.0 SP04 PL08 and below

KBA , BC-SYB-REP-SAP , Replication with SAP Suite / SAP BW , Problem