Re: Rollback writes >highwater mark size

The number of bytes written can be significantly higher than the HWM size. This is because the number of bytes written is since instance startup. One transaction can write X bytes to the rollback segment. After that transaction is complete, another transaction can write Y bytes to the same rollback segment. The HWM size will be the greater of X and Y. But yet the number of bytes written will be X+Y. Since X & Y > 0, X+Y will always be larger than the greater of X and Y.

HTH,
Brian

michael ngong wrote:
>
> Database Enterprise Edition 8.1.7.0.0
> OS 8.1.7 Hp Unix 11.0
>
> It is kind of interesting that the rollback stats below almost
> consistently show the HWMSIZE is lower than the writes.
> I also expected some of the rollback segments to have optimal size as
> a result of shrinking.
>
> Configuration of initial and next..Initial extent 4194304 next_extent
> 4194304
> Just in case your documentation is far away below are the definitions
> from the docs for a reminder.
> WRITES
> The number of bytes of entries written to the rollback segment.
>
>
> OPTSIZE
> The value of the optimal parameter for the rollback segment.
>
> HWMSIZE
> The highest value (high water mark), in bytes, of the rollback
> segment size reached during usage.
>
> SHRINKS
> The number of shrinks that the rollback segment has had to perform in
> order to stay at the optimal size.
>
> WRAPS
> The number of times a rollback segment entry has wrapped from one
> extent to another.
>
> EXTENDS
> The number of times that the rollback segment had to acquire a new
> extent.
>
>
>
> SQL> select writes,optsize,hwmsize,shrinks,wraps from v$rollstat;
>
> WRITES OPTSIZE HWMSIZE SHRINKS WRAPS
> ---------- ---------- ---------- ---------- ----------
> 2580 5251072 0 0
> 121459630 16777216 109682688 3 33
> 52427030 16777216 16867328 0 15
> 39317908 16777216 16867328 0 11
> 140816400 16777216 113901568 3 39
> 167348988 33554432 117547008 1 23
>
> Appreciater your input as usual
>
> Michael Tubuo Ngong

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