Hello Kjell,

>> * In merge state new pages are not allocated from difference files.
>> Writes go to the main database files. Reads of mapped pages compare
>> both page versions and return the version which is fresher, because
>> we don't know if it is merged or not.
>
> I don't quite understand this, and perhaps I'm beating a dead horse...
> But... I just want to get a grasp on how this works... :-)
>
> I assume "mapped pages" are pages that were updated during stalled
> state, and thus have a newer version in the delta than in the main file.

Yes, those pages are said to be "mapped out" to the delta file.

> 1. Main file contains page rev 1.
> (...)
> 9. Merge finishes.

That's exactly how I understand it.

> This would appear to work and be consistent with the quoted text above,
> although I did find the text somewhat unclear.

Not everybody is fluent in English. If you want to make sure that your
(and my) assumptions are correct, you could contact Nikolay, or ask
Sean Leyne, his then-boss, who assigned him the nbackup task. Both are
active on firebird-devel, so you can pick up their email addresses
easily.


Cheers,
Paul Vinkenoog