Re: BUG #17064: Parallel VACUUM operations cause the error "global/pg_filenode.map contains incorrect checksum"

On 24/06/2021 11:06, Thomas Munro wrote:
> On Thu, Jun 24, 2021 at 7:52 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>> On 23/06/2021 12:45, Thomas Munro wrote:
>>> On Wed, Jun 23, 2021 at 7:46 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>>>> Let's just add the lock there.
>>>
>>> +1, no doubt about that.
>>
>> Committed that. Thanks for the report, Alexander!
> 
> I think you missed relmap_redo (including a misleading comment).

Fixed, thanks!

>> If anyone wants a write a patch for that, I'd be happy to review it. And
>> if anyone has access to a system with pmem hardware, it would be
>> interesting to try to reproduce a torn sector and broken control file by
>> pulling the power plug.
> 
> I have been working on a kind of experimental file system for
> simulating torn sectors (and other interesting file system phenomena)
> as part of some work on recovery scenerio testing, not quite ready to
> share yet but it can simulate that exact failure...

Cool! We know what happens if pg_control file is torn, though. What I'd 
like to know is whether it can happen in practice with pmem, an how 
likely it is. For curiosity mostly, I think we have already established 
that it can happen, and it would be nice to protect against it in any 
case, even if it's rare.

- Heikki