Re: Oracle 10g - flashback database questions

Kenneth Koenraadt wrote:
> On Mon, 16 May 2005 12:50:18 +0200, "Matthias Hoys"
> <idmwarpzone_NOSPAM__at_yahoo.com> wrote:
>
> >OK I admit I haven't done much research into this but i'm just
looking for
> >some hands-on experience.
> >
> >Oracle 10g supports the FLASHBACK DATABASE feature. This allows to
do a
> >recovery based on information stored in a flashback area (flashback
logs).
> >
> >Now my questions :
> >1) Can you use flashback database to do a complete db point-in-time
recovery
> >?
> Yes.
>
> >2) Can flashback database be combined with/followed by a "normal"
recovery
> >using the archive log files ?
>
> No.
>
> >3) Does archive logging need to be enabled for flashback database to
work ?
> Yes.
>
> >Or can this work independently of each other ?
> >4) How much (extra) diskspace is needed to store the flashback logs
in
> >comparison to the diskspace consumed by archive log files ?
>
> The flashback logs store change in DB blocks, supplementing the
> content in the undo segments to enable flashback. The more blocks are
> changed, the more flashback log is generated. Measure it! My
(limited)
> experience says that flashback logs do take much less space than
> archive logs (no big surprise) but that the actual amount varies
> between different systems.
>
> >5) What if you start flashing back a database and something goes
wrong
> >(example a corrupt flashback log file) ? Is recovery possible of
corrupt
> >flashback log files ? Or can the flashback operation be rolled back
?
>
> Then you are most likely out of luck. That is why you still and
always
> need your physical backup.
> About "rolling back" : You can flashback forth and back as much as
you
> want within the time/SCN-range given by your undo tablespace and
> FLASHBACK_RETENTION_TARGET. You can even open the database in read
> only mode and see if the point in time you reached is the right one
> and then flashback or forth until you have opened the database with
> RESETLOGS.
>
> >6) Is FLASHBACK TABLE using the same flashback log files (if it's
enabled)
> >or does it still use the undo records ?
>
> Flaskback table is a totally different thing, does not use flashback
> logs and is enabled even when flashback database is disabled.
>
> >7) A flashback database recovery operation is supposed to be faster
than a
> >recovery using the archive log files. What is the recovery gain that
can be
> >expected ? Any ways of tuning the recovery process ? Can flashback
database
> >be performed in parallel ?
> The flashback database is in no way intended to replace your physical
> backup/recovery. Its only purpose is to recover from user errors. Of
> course it will be "faster" than a physical restore+recovery, because
> no restore of files from tape etc. is necessary.
>
> AFAIK, flashback does not come with a PARALLEL option.
>
> Also note that enabling flashback is not free: The continous
> generation of flashback logs becomes a permanent extra I/O-workload
on
> your system.
>
> >8) Oracle 10g Release 2 : will this new version have some
additional/fixed
> >flashback database features ?
> Wait and see. You could hope for the PARALLEL option :-)
> >
> >
> >Thanks in advance,
> >Matthias
> >
> >
>
> - Kenneth Koenraadt

Does any one see need for using FLAHSBACK Database in production environments. I do see it being useful in development environments where user errors could be many, but in production environment, I do not see much advantage considering that there is performance overhead in generating flash back logs.

Prem Received on Mon May 16 2005 - 21:54:20 CDT