Flashback database question

[usenet]

10.2.0.3

SQL> select sysdate from dual;

SYSDATE
-------------------
09/26/2007 15:02:07

SQL> select OLDEST_FLASHBACK_TIME,RETENTION_TARGET from v
$flashback_database_log;

OLDEST_FLASHBACK_TI RETENTION_TARGET
------------------- ----------------
09/24/2007 23:53:12 360

Since RETENTION_TARGET is 360 (6 hours), how come the
OLDEST_FLASHBACK_TIME can be way beyond 6 hours?

Thanks!

[usenet]

a écrit dans le message de news: 1190835448.931165.54480@57g2000hsv.googlegroups.co m...
| 10.2.0.3
|
| SQL> select sysdate from dual;
|
| SYSDATE
| -------------------
| 09/26/2007 15:02:07
|
| SQL> select OLDEST_FLASHBACK_TIME,RETENTION_TARGET from v
| $flashback_database_log;
|
| OLDEST_FLASHBACK_TI RETENTION_TARGET
| ------------------- ----------------
| 09/24/2007 23:53:12 360
|
| Since RETENTION_TARGET is 360 (6 hours), how come the
| OLDEST_FLASHBACK_TIME can be way beyond 6 hours?
|
| Thanks!
|

Oracle did not need to reuse space so it kept older transactions.

Regards
Michel

[usenet]

On Sep 26, 4:05 pm, "Michel Cadot" wrote:
> a écrit dans le message de news: 1190835448.931165.54...@57g2000hsv.googlegroups.co m...
> | 10.2.0.3
> |
> | SQL> select sysdate from dual;
> |
> | SYSDATE
> | -------------------
> | 09/26/2007 15:02:07
> |
> | SQL> select OLDEST_FLASHBACK_TIME,RETENTION_TARGET from v
> | $flashback_database_log;
> |
> | OLDEST_FLASHBACK_TI RETENTION_TARGET
> | ------------------- ----------------
> | 09/24/2007 23:53:12 360
> |
> | Since RETENTION_TARGET is 360 (6 hours), how come the
> | OLDEST_FLASHBACK_TIME can be way beyond 6 hours?
> |
> | Thanks!
> |
>
> Oracle did not need to reuse space so it kept older transactions.
>
> Regards
> Michel

Thnx, but my question is since RETENTION_TARGET is 6 hours, does this
mean I only can flashback database up to 6 hrs ago? If so, how come
the OLDEST_FLASHBACK_TIME is way more than 6 hrs?

[usenet]

On Sep 27, 6:19 am, jackzh...@gmail.com wrote:
> On Sep 26, 4:05 pm, "Michel Cadot" wrote:
>
>
>
> > a écrit dans le message de news: 1190835448.931165.54...@57g2000hsv.googlegroups.co m...
> > | 10.2.0.3
> > |
> > | SQL> select sysdate from dual;
> > |
> > | SYSDATE
> > | -------------------
> > | 09/26/2007 15:02:07
> > |
> > | SQL> select OLDEST_FLASHBACK_TIME,RETENTION_TARGET from v
> > | $flashback_database_log;
> > |
> > | OLDEST_FLASHBACK_TI RETENTION_TARGET
> > | ------------------- ----------------
> > | 09/24/2007 23:53:12 360
> > |
> > | Since RETENTION_TARGET is 360 (6 hours), how come the
> > | OLDEST_FLASHBACK_TIME can be way beyond 6 hours?
> > |
> > | Thanks!
> > |
>
> > Oracle did not need to reuse space so it kept older transactions.
>
> > Regards
> > Michel
>
> Thnx, but my question is since RETENTION_TARGET is 6 hours, does this
> mean I only can flashback database up to 6 hrs ago? If so, how come
> the OLDEST_FLASHBACK_TIME is way more than 6 hrs?

The word "target" has a specific meaning in English: things such as
arrows, bullets and undo retention are allowed to miss targets by a
wide mile!

You've asked for 6 hours of undo retention. Oracle will do its best to
achieve this. Undo younger than 6 hours will not be overwritten (or
we'll try not to, anyway). Undo older than 6 hours **may** (not
"will") be over-written by fresh undo.

But if you do so few transactions that the cavernous wastes of your
undo tablespace don't stand a chance in hell of ever being filled to
the brim, it stands to reason that undo older than 6 hours can safely
be left to sit around un-overwritten. And that means the undo needed
to flash back further than 6 hours is still available -and therefore
yes, of course you are allowed to use that undo to perform flashback
to the oldest time for which undo happens to still be available.