On Wed, 2002-08-07 at 11:52, Richard Tucker wrote:
>
>
> If you don't duplicate(mirror) the log then in the event you need to restore
> a database with roll forward recovery won't the restored database be missing
> on average 1/2 a log segments worth of changes?
>
The xlog code must allow us to force an advance to the next log file,
and truncate the archived file when it's copied so as not to waste
space. This also prevents the sysadmin from confusing two logfiles with
the same name and different data.
This complicates both the recovery logic and XLogInsert, and I'm trying
to kill the "last" latent bug in that feature now. Hopefully I can even
convince myself that the code is correct and covers all the cases.
As a side effect, the refactoring of XLogInsert makes it easy to add a
special record as the first XLogRecord of each file. This can contain
information useful to the system administrator, like what database
installation the file came from. Since it's at a fixed offset after the
page header, external tools can read it in a simple way.
--
J. R. Nield
jrnield@usol.com