>From: "Bryan O'Halloran" <[log in to unmask]>
>Subject: Dynamic rollback
>
>I need to institute Dynamic Rollback Recovery for my databases because it is
>taking me two hours to recover from a System Abort and I need to shorten the
>time dramatically.
<>
>Can someone with experience of a medium size HP3k (300 to 400 users) advise if
>dynamic rollback recovery will work in practice or should I continue being
ultra
>cautious.
 
Bryan,
 
 We converted all our roll-forward recoveries to roll-back before going to
MPE 5.0 release to shorten any downtimes.  Our implementation was done in
such a way as to use roll forward as a "last resort" method if roll back failed.
 
 Since going to 5.0, we did 2 rollback database recoveries that total 17 log
identifiers and 40+ databases.  They worked as planned (avg downtime 1.5 to
2 hours for roll-back instead of 5 hours for roll forward with lots of risk
of wrong tapes or bad tapes).
 
Here is our sequence of settings:
=================================
<set the flags before backups:  Normally, databases will be enabled for
rollback but sometimes maintenance will remove this flag.  The following
<stupid!> sequence enables a database for rollback then disables it for
rollback because a <junior?> HP programmer put in a verify prompt that you
can't predict in a batch job.  For example, If rollback was not enabled, the
"Y" following the "disable rollback" produces an error (jcw=99).  To prevent
an error, you enable rollback before disabling it. sigh :-( >
 
!RUN DBUTIL.PUB.SYS
ENABLE  DB       FOR  ROLLBACK
DISABLE DB       FOR  ROLLBACK
Y
ENABLE  DB       FOR  RECOVERY
DISABLE DB       FOR  ACCESS,LOGGING
 
<so far, simple roll forward method:  Backup databases here>
 
!RUN DBUTIL.PUB.SYS
DISABLE DB       FOR  RECOVERY
ENABLE  DB       FOR  ACCESS,ROLLBACK
Exit
 
<at this point, databases enabled for rollback but stored on tape with roll
forward flags set.  In the event of roll-back failure, you do roll-forward
method>
 
Sample roll-back Recovery job (notice roll-back still needs "recovery" flag
on to work, so we turn it on and off:)
===================
!RUN DBUTIL.PUB.SYS
ENABLE DB FOR RECOVERY
EXIT
!EOD
!if JCW = 99 then
!  tellop *****  DB JOB ERROR  **************
!  tellop *****  error in setting database flags *
!  tellop ***********************************
!  eoj
!endif
!RUN DBRECOV.PUB.SYS
ROLLBACK  DB
RUN
!EOD
!RUN DBUTIL.PUB.SYS
DISABLE DB FOR RECOVERY
EXIT
!EOD
!if JCW = 99 then
!  tellop *****  DB JOB ERROR ***************
!  tellop *****  error in setting database flags *
!  tellop ****************************************
!  eoj
!endif
!EOJ
----------------------------------------------------------------
Eric J. Schubert                    Senior Data Base Analyst
Office of Information Technologies  Univ of Notre Dame, IN USA
(219) 631-7306                      http://www.nd.edu/~eschuber