RE: Log Shipping and Full Backup Frequency. Advice?
From: AnthonyThomas (AnthonyThomas_at_discussions.microsoft.com)
Date: 11/02/04
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Date: Tue, 2 Nov 2004 06:02:01 -0800
They way to think of this is that the database, and it's files, are just
state variables: they only contain within them the values at any particular
point in time.
The transaction log is different; it is a recording of database actions.
Similar to the General Ledger in an accounting system.
Full, Differential, and File Group backups only backup the state of the
database. And, if you restore from any of these, you only get that state.
This is not the case with the transaction log or its backups. They are
independent. However, since the tansaction log contains action against the
database, it also notes when and at what state the database was in whenever a
full, differential, and/or filegroup backup was initiated and completed.
You need at least one Full backup, and maybe the others if you wish, to
create the initial database state. However, from that point forward,
restoring transaction log backups only to this system would be EXACTLY like
having every user who had logged in, relog in and execute every statement
just as it had occurred originally. It is, in essence, a replay of the
system activity, as far as database modifications go.
That is whay third-party tools that can read the transaction logs and there
backups so worth while: they can undo individual and/or sequences of
transactions.
This all supposes that you are running in FULL RECOVERY mode. If you are
running in BULK INSERT reocery, there will be gaps in the sequence. And, if
you are running in SIMPLE mode, you can not even backup the transaction log,
only the state backups described above.
Hope this helps.
Sincerely,
Anthony Thomas
"LCaffrey" wrote:
> Hi,
>
> After I do a full restore to a target reporting box, I continue
> refreshing the target with shipped transaction logs. Is there a limit
> to the amount of transaction logs that can be shipped before doing
> another full restore. For example and being extreme, could I continue
> shipping logs for 6 months or 1 year without a full restore?
>
> Also, I notice that full backups on the source box do not interfere
> with the LSN of the shipped transaction logs. Is this consistent with
> other people's experience. (i.e. transaction logs are backwardly
> compatible with all previous full backups as long as you have an
> unbroken sequence of transaction log files from that particular full
> backup).
>
> Regards
>
> Liam Caffrey
>
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