On Mon, Aug 26, 2013 at 4:57 AM, 高健 <luckyjackgao@gmail.com> wrote:
> But why "writes the entire content of each disk page to WAL "?
>
The documentation states that: "The row-level change data normally
stored in WAL will not be enough to completely restore such a page
during post-crash recovery.". I guess that a mixed page (i.e., a page
that contains old and new data) cannot be safely recovered with
deltas, so you need to have a "clean" page image to which start
recovery.
Someone with more internal knowledge can comment on this.
Luca