Re: Logical to physical page mapping

Jan Wieck <JanWieck@Yahoo.com> writes:
> The reason why we need full_page_writes is that we need to guard against 
> torn pages or partial writes. So what if smgr would manage a mapping 
> between logical page numbers and their physical location in the relation?

> At the moment where we today require a full page write into WAL, we 
> would mark the buffer as "needs relocation". The smgr would then write 
> this page into another physical location whenever it is time to write it 
> (via the background writer, hopefully). After that page is flushed, it 
> would update the page location pointer, or whatever we want to call it. 
> A thus free'd physical page location can be reused, once the location 
> pointer has been flushed to disk. This is a critical ordering of writes. 
> First the page at the new location, second the pointer to the current 
> location. Doing so would make write(2) appear atomic to us, which is 
> exactly what we need for crash recovery.

I think you're just moving the atomic-write problem from the data pages
to wherever you keep these pointers.

			regards, tom lane