Re: WAL replay bugs

On 06/13/2014 10:14 AM, Michael Paquier wrote:
> On Mon, Jun 2, 2014 at 9:55 PM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
>> On Wed, Apr 23, 2014 at 9:43 PM, Heikki Linnakangas
>> <hlinnakangas(at)vmware(dot)com> wrote:
>> Perhaps there are parts of what is proposed here that could be made
>> more generalized, like the masking functions. So do not hesitate if
>> you have any opinion on the matter.
> OK, attached is the result of this hacking:
>
> Buffer capture facility: check WAL replay consistency
>
> It is a tool aimed to be used by developers and buildfarm machines
> that can be used to check for consistency at page level when replaying
> WAL files among several nodes of a cluster (generally master and
> standby node).
>
> This facility is made of two parts:
> - A server part, where all the changes happening at page level are
> captured and inserted in a file called buffer_captures located at the
> root of PGDATA. Each buffer entry is masked to make the comparison
> across node consistent (flags like hint bits for example) and then
> each buffer is captured is with the following format as a single line
> of the output file:
> LSN: %08X/%08X page: PAGE_IN_HEXA
> Hexadecimal format makes it easier to detect differences between
> pages, and format is chosen to facilitate comparison between buffer
> entries.
> - A client part, located in contrib/buffer_capture_cmp, that can be
> used to compare buffer captures between nodes.

Oh, you moved the masking code from the client tool to the backend. Why?
When debugging, it's useful to have the genuine, non-masked page image
available.

- Heikki