Re: [HACKERS] Checksums by default?

On Thu, Jan 26, 2017 at 9:22 AM, Andres Freund <andres@anarazel.de> wrote:
> On 2017-01-26 09:19:28 +0900, Michael Paquier wrote:
>> On Thu, Jan 26, 2017 at 9:14 AM, Peter Geoghegan <pg@heroku.com> wrote:
>> > On Wed, Jan 25, 2017 at 3:30 PM, Stephen Frost <sfrost@snowman.net> wrote:
>> >> As it is, there are backup solutions which *do* check the checksum when
>> >> backing up PG.  This is no longer, thankfully, some hypothetical thing,
>> >> but something which really exists and will hopefully keep users from
>> >> losing data.
>> >
>> > Wouldn't that have issues with torn pages?
>>
>> Why? What do you foresee here? I would think such backup solutions are
>> careful enough to ensure correctly the durability of pages so as they
>> are not partially written.
>
> That means you have to replay enough WAL to get into a consistent
> state...

Ah, OK I got the point. Yes that would be a problem to check this
field on raw backups except if the page size matches the kernel's one
at 4k.
-- 
Michael