Re: Uncommitted Data

<agarwalp_at_eeism.com> wrote in message
news:1118907481.988226.229770_at_o13g2000cwo.googlegroups.com...
> The only thing i am not clear about is, If the data files contains
> following dirty blocks
>
> update table set col1=2 where col1=3
> update table set col1=4 where col1=5
> Check point
> update table set col1=6 where col1=7
>
> Database crashes
>
> Then i believe with the checkpoint information in the Log file only
> first two will be rolled forward and the third will be lost since it is
> niether followed by commit or checkpoint.

No. The first two changes won't be rolled forward because they are already there, on the disk, in the datafile. Only the last one will be rolled forward,
Subsequently, all three will be rolled 'backwards' and the changes will be lost since none was committed. Besides, there is no 'checkpoint information' in the log file. Why don't you read the stuff HansF provided links for ? It's pretty simple.

> if the above is true, then what happens during the crash whick makes
> redo log roll forward the dirty blocks even though they are in the
> datafiles.

If the blocks are in the datafile, they are not dirty any more by definition.
>
Received on Thu Jun 16 2005 - 05:31:13 CDT