Interesting scenario, is there a need to reset logs periodically?

Question

10.2.0.2 Ent Ed -- Rman 10.2.0.2 -- aix 5.3
Is there a possible need to perform a reset logs periodically? This question initially came to me at the worst of times, during a recovery of a fairly important database.
If / when you have to perform an spfile or controlfile restore without a recovery catalog, if your log sequence is above 255 and your last backup was more than a day ago, is it possible your latest autobackup wont be found? In our scenario we had a day old controlfile snapshot that we used, but I'm not sure if we would have been able to recover had it not been there. From reading the 10g Recovery Manager Reference manual:
"FROM AUTOBACKUP
[autoBackupOptionList]
Restores a control file autobackup. You can only specify this option on the RESTORE CONTROLFILE and RESTORE SPFILE commands. When restoring either type of file in NOCATALOG mode, the FROM AUTOBACKUP clause is required.
RMAN begins the search on the current day or on the day specified with the SET UNTIL. If no autobackup is found in the current or SET UNTIL day, RMAN checks the previous day starting with sequence 256 (or the sequence specified by MAXSEQ) until it reaches 0. The search continues up to MAXDAYS days (default of 7, maximum of 366) from the current or SET UNTIL day. If no autobackup is found within MAXDAYS days, then RMAN signals an error and the command stops. "
The doc doesn't mention it but if you haven't ever tried setting MAXSEQ > 256, you'll get an error if you do. 256 is the upper bound for the MAXSEQ parameter. This is a snippet from my test of that:
<code>
oracle_sandbox1> rman target /
Recovery Manager: Release 10.2.0.2.0 - Production on Fri Nov 21 09:16:36 2008
Copyright (c) 1982, 2005, Oracle. All rights reserved.
connected to target database: WEBDEV (DBID=1965364971)
RMAN> show all;
using target database control file instead of recovery catalog
RMAN configuration parameters are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 5;
CONFIGURE BACKUP OPTIMIZATION OFF; # default
CONFIGURE DEFAULT DEVICE TYPE TO 'SBT_TAPE';
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE SBT_TAPE TO '%F'; # default
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F'; # default
CONFIGURE DEVICE TYPE SBT_TAPE PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/app/oracle/product/10.2/dbs/snapcf_webdev.f'; # default
RMAN> run {
2> allocate channel t1 type 'SBT_TAPE';
3> restore spfile to pfile '/app/oracle/product/10.2/dbs/webdev_pfile.tst' from autobackup maxseq=300;
4> }
allocated channel: t1
channel t1: sid=256 devtype=SBT_TAPE
channel t1: Veritas NetBackup for Oracle - Release 6.5 (2007111606)
Starting restore at 21-NOV-08
released channel: t1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 11/21/2008 09:23:46
RMAN-06494: MAXSEQ = 300 is out of range (0-255)
RMAN>
</code>

Answer 1

The "sequence" here is not the Log Sequence Number that is assigned when LGWR switches from one Redo Log to another, and the previous one is archived out as an Archivelog (if running in ARCHIVELOG mode).
The "sequence" here is the sequence of the controlfile autobackup that was created. In AUTOBACKUP mode every change to the database structure (eg adding a new datafile) causes an Autobackup. Similarly, every Database Backup causes an Autobackup. Since multiple such autobackups can occur within a single day, Oracle assigns a SEQUENCE to differentiate beteween the backups created on the same day. It is this sequence that is limited to 255 .
Hemant K Chitale
http://hemantoracledba.blogspot.com