On Tue, Dec 05, 2000 at 10:43:03AM -0800, Mikheev, Vadim wrote:
> > As far as I know (and have tested in excess) Informix IDS
> > does survive any power loss without leaving the db in a
> > corrupted state. The basic technology is, that it only relys
> > on writes to one "file" (raw device in that case), the txlog,
> > which is directly written. All writes to the txlog are basically
> > appends to that log. Meaning that all writes are sync writes to
> > the currently active (== last) page. All other IO is not a problem,
> > because a backup image "physical log" is kept for each page
> > that needs to be written. During fast recovery the content of the
> > physical log is restored to the originating pages (thus all pendig
> > IO is undone) before rollforward is started.
>
> Sounds great! We can follow this way: when first after last checkpoint
> update to a page being logged, XLOG code can log not AM specific update
> record but entire page (creating backup "physical log"). During after
> crash recovery such pages will be redone first, ensuring page consistency
> for further redo ops. This means bigger log, of course.
Be sure to include a CRC of each part of the block that you hope
to replay individually.
Nathan Myers
ncm@zembu.com
