[Info-ingres] Incremental rollforwarddb sessions connected

[Paul White]

Hello all Ingres architects and interested participants,

 

I was wondering about the feasiblilty of an enhancement to rollforwarddb to
allow the incremental operation run whilst other sessions are connected,
similar to online checkpoint, waiting for open transactions to complete.

 

To fill you in.. Over the years, I have developed set of tools which
maintain a replica database and synchronising from production every xx
minutes using journal log shipping.  The target database is read-only used
for disaster recovery, journal analysis and occasional reports.  At one
site, I am using the replica to support web services.

 

If you are new to the concept, this makes very good reading:

 

https://www.actian.com/company/blog/ingres-actian-x-disaster-recovery/

 

Compared to other replication options, I have found the journal "log
shipping" method to be light weight and negligible impact on the production
server.  Maintenance requirements are infrequent and problems are rare.
And, best of all it works out of the box without additional software.

 

My script terminates connections before running incremental rollforwarddb on
the target server.  This is a requirement of rollforwarddb.  Periodically it
runs a full refresh from the latest checkpoint.

 

I'd like to know if it is worth putting in an enhancement request to relax
the restriction, allowing the synchronise to run whilst sessions are
connected.  I imagine various cache flushes (dm421, dm422, rd10) would be
required. If there is a session in progress, there needs to be DB level
lock,  similar to CKP lock, to prevent a new transaction from starting.   If
the target database is in high demand, I plan to ensure the duration of
incremental rolls are minimal.

 

 

Paul White

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