>I think any REAL database should flush the buffers on each and every commit.
>That's what commit is here for.
This doesn't seem to be right as the write ahead log is used to recover if the data in
the cache is lost because of the inproper shutdown. But SAP DB has the feature to
switch this log off. There is a limited set of the applications that might benefit of this.
For my appl this is very useful feature if it gives me the perf. increase for the cost of
possible data lost (as SAP DB kernel + OS is quite stable with proper
configuration it will be very rare case). But the problem is that it seems SAP DB
starts writing data synchronously as the log is disabled. Probably my guess is
wrong but it seems so...I'm writing a lot of blobs..probably this makes things worse.
Dmitri
Peter Willadt <[EMAIL PROTECTED]> wrote:
Hello,
On Freitag, 28. M�rz 2003 10:16, Dmitri Lyssenko wrote:
>
> It appeared from the test that if the log writer is disabled (that I
> believed give me the best performance) the database starts flushing the data
> cache very often...probably on each commit.
> This guess is originated from the look at the "vmstat" output
> (however I might be wrong). As result having these 2 options together (SET
> LOG WRITER OFF and USE_O_DIRECT YES) gave me the worst performance.
> Is it right that the frequencity of the savepoints depends on the state of
> the log writer (disabled/enabled)...and therefore O_DIRECT should not be
used with the log switched off?
>
I think any REAL database should flush the buffers on each and every commit.
That's what commit is here for.
Peter Willadt
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