[EMAIL PROTECTED] wrote:
>
> Quoting Sven K�hler <[EMAIL PROTECTED]>:
>
> >
> > INSERTs/UPDATEs are a bit slow ... SAPDB might as fast as
> MySQL if you
> > set the LogMode to DEMO (which means, that no transaction-log is
> > written), but that's not a good idea in general.
> >
>
> I thought that the difference between demo and single was
> when the log was full:
>
> in demo mode you have :
> if (log is full) {
> truncate log file
> }
>
> in single mode you have :
> if (log is full) {
> take the big kernel lock
> backup log
> truncate log file
> release the big kernel lock
> }
>
>
> So if you have an hypothetical infinite size (i.e. never
> full) log, single==demo.
Oops, in a real database where you have productive data this
is no good idea.
A much better idea is not to wait until log is full ,
but to use the automatic saving of log, which is done
every time when log is filled up to some amount.
It will not overwrite older log-backups, but will give you
a number of consecutive log backups which will be really
helpful in case of a damaged database.
If you do NOT have log-backups, only your last data backup
can be used (which often is too old, let's say a week, for a
real productive database). Then your only chance to recover
to the last finished transaction before the damage (disc crash
or whatever) is to recover this data backup and all the log-backups
done after this.
But if you do not have such backups because of logmode demo:
good night and have a nice time with your boss and all those
guys who will have to check and type those changes lost
because of missing log-backups.
Logmode DEMO is for playing around, but not for
productive databases.
Elke
SAP Labs Berlin
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