August 20, 2009 at 8:46 pm
I haven't worked in an Oracle shop so I never heard the term before. The closest term I am familiar with is a "cold start" and that meant everything on disk was trash and required an entire reload of the OS, programs, and database/datafiles. I got real good at those while stationed in England. For over six months I was doing one every week on our Burroughs B3500.
August 21, 2009 at 9:32 am
I want to make this topic more interesting.
Take a scenario when the DB is online and transactions are open and some work is going on (insert, update, delete).
Now my friend starts FULL Backup or any backup for this DB. How would server decide when to issue the checkpoint state? Is CHECKPOINT is issued as soon as the backup is started. Any thoughts!!
-LK
August 21, 2009 at 9:34 am
luckysql.kinda (8/21/2009)
I want to make this topic more interesting.Take a scenario when the DB is online and transactions are open and some work is going on (insert, update, delete).
Now my friend starts FULL Backup or any backup for this DB. How would server decide when to issue the checkpoint state? Is CHECKPOINT is issued as soon as the backup is started. Any thoughts!!
-LK
It backs it up in the state it's in when the command is issued. That means those would be in the log backup as incomplete transactions. That way, if you have a later log backup that has those as completed, they can be rolled forward.
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August 21, 2009 at 9:45 am
The backup starts throwing out pages. If a page changes while the backup is running, the associated log records are then put in the backup at the end for roll back/roll forward when you restore. If the transaction isn't committed, the changes aren't in the backup.
August 21, 2009 at 9:56 pm
- A cold backup, also called an offline backup, is a database backup when the database is offline and thus not accessible for updating. This is the safest way to back up because it avoids the risk of copying data that may be in the process of being updated. However, a cold backup involves downtime because users cannot use the database while it is being backed up.
When system downtime must be minimized, a hot backup can provide an alternative to the cold backup. A hot backup can be done even as users access the database, but some method must be used to ensure that data being updated is noted and can be copied when the update is complete.
August 22, 2009 at 7:59 am
There is no risk of changing data in a hot backup in SQL Server. The log records are used to ensure this is completely safe.
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