Re: tuning questions

On Thu, Dec 04, 2003 at 11:59:32AM -0500, Jeff wrote:
> On Thu, 04 Dec 2003 08:06:23 -0800
> Jack Coates <jack(at)lyris(dot)com> wrote:
>
> > testbed:
> > dual P3 1.3 GHz box with 2GB RAM
> > two IDE 120G drives on separate channels (DMA on), OS on one, DB on
> > the other, some swap on each (totalling 2.8G).
> > RH Linux 8.
>
> Side Note: be sure to turn off write caching on those disks or you may
> have data corruption in the event of a failure

I've seen this comment several times from different people.
Would someone care to explain how you would get data corruption? I
thought that the whole idea of the log is to provide a journal similar
to what you get in a journaling file system.

In other words, the db writes a series of transactions to the log and marks
that "log entry" (don't know the right nomeclature) as valid. When the db
crashes, it reads the log, and discards the last "log entry" if it wasn't
marked as valid, and "replays" any transactions that haven't been
commited ot the db. The end result being that you might loose your last
transaction(s) if the db crashes, but nothing ever gets corrupted.

So what am I missing in this picture?

Regards,

Dror

--
Dror Matalon
Zapatec Inc
1700 MLK Way
Berkeley, CA 94709
http://www.fastbuzz.com
http://www.zapatec.com