Re: Long Transaction

From: Edward Rosenthal <edrosenthal@home.com> > >Er....I have the distinctive aroma of cow pats in my nose...where does the >physical log get retrieved, exactly? >i love the image. anyway >i'm from petaluma, calif. and we have plenty of cows. I'm sure you do. But isn't it illegal? >i was thinking, and correct me if i'm wrong, (i'm sure you will!) >that each time the buffer is modified there has to be an io write to the Well, not quite. Every time a previously unmodified buffer is modified. If the buffer was already "dirty", it doesn't get rewritten to the physical log. >physical log >to keep the before image handy, for a rollback(?). this comes from the >buffer >from >the read cache ...as each buffer modification takes place the physical log >is >keeping before image rows by having the cache write to it. >when the 75% is reached,or a checkpoint, the physlog is written to the >database, Well, no. The physical log isn't written to the database at all. It's only used for rollback. Once the flush of modified buffers is complete, the physical log is simply truncated. >and flushed. >and because the next buffer modification needs the next before image, >the physical log needs to have the before image written to from the >database... >hence, the "retrieval"... Right. I've never heard a write described as a retrieval before. My mistake, I'm sure. ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com