Re: BUG #4879: bgwriter fails to fsync the file in recovery mode

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> I would like an explanation of why minimum recovery point needs to
>> be advanced at all. If there's any use for it, it is surely part
>> of functionality that is not there in 8.4.

> It gives protection against starting up the database too early.

Protection against what failure scenario?

> It stops
> the database from starting up if you stop recovery, and move recovery
> target backwards or delete WAL files from pg_xlog, in a way that's not
> safe. Of course, that's a case of "don't do that!", but it's a mistake
> you can make when trying to manually recover to a given point in time.

You can't move the target backwards --- it's embedded in pg_control.
And even if you could, I don't see what protection this particular
mechanism gives you. To the extent that it does anything at all, it's
going to be full of holes because it only examines pages that happen to
be dirtied by (the current instance of) the recovery process.

regards, tom lane