Re: WAL replay bugs

On Fri, Jun 13, 2014 at 4:50 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
> On Fri, Jun 13, 2014 at 4:48 PM, Heikki Linnakangas
> <hlinnakangas@vmware.com> wrote:
>> On 06/13/2014 10:14 AM, Michael Paquier wrote:
>>>
>>> On Mon, Jun 2, 2014 at 9:55 PM, Michael Paquier
>>> <michael.paquier@gmail.com> wrote:
>>>>
>>>> On Wed, Apr 23, 2014 at 9:43 PM, Heikki Linnakangas
>>>> <hlinnakangas@vmware.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.
> My thought is to share the CPU effort of masking between backends...
And that having a set of API to do page masking on the server side
would be useful for extensions as well. Now that I recall this was one
of the first things that came to my mind when looking at this
facility, thinking that it would be useful to have them in a separate
file, with a dedicated header.
-- 
Michael