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Home -> Community -> Usenet -> c.d.o.server -> Re: Oracle 10g - flashback database questions
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
>
>