Re: Hot Backup Issue

From: Don Granaman <granaman_at_home.com>
Date: Tue, 02 Oct 2001 06:33:33 -0700
Message-ID: <F001.0039E922.20011002052525@fatcity.com>

The main disadvantage of #1 is that lgwr will write full blocks to the redo logs for the entire database until the entire backup is finished. If that takes a while and there is significant activity, it can generate tremendous amounts of redo - and archive. Lgwr and the I/O subsystem are doing more work since they are writing more data. This is what I have do when using EMC and BCV splits for backups since it is so fast.

#2 is, in my opinion, better for any "normal" backups - such as to tape. Since only one tablespace at a time is in backup mode, redo and archive generation is minimized. This is especially true if only a relatively small fraction of the database is undergoing significnant transactional activity. The length of time when lgwr is writing full blocks for those transactions is only as long as it takes to back up those particular tablespaces, not all tablespaces.

-Don Granaman

[OraSaurus - Honk if you remember UFI!]

Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, October 02, 2001 6:15 AM

Hello,

Slightly unrelated question... is it better to (in pseudo code) :

for each tablespace loop
put tablespace in backup mode
end loop

for each datafile in the database loop
copy data file
end loop

for each tablespace loop
put tablespace in normal mode
end loop

or 2)

for each tablespace loop
put tablespace in backup mode
for each datafile in this tablespace loop copy data file
end loop
put tablespace in normal mode
end loop

What I'm doing is (2), but I notice that Rajesh is doing (1). What are the pros and cons of each approach? (I'll probably use RMAN at some point, anyway :0) ).

Cheers,

--

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--

Author: Don Granaman
INET: granaman_at_home.com

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