Re: 16-bit page checksums for 9.2

On Sun, Jan 8, 2012 at 2:03 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On Sat, Jan 7, 2012 at 11:09 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> On Sat, Jan 7, 2012 at 10:55 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>
>>> So there isn't any problem with there being incorrect checksums on
>>> blocks and you can turn the parameter on and off as often and as
>>> easily as you want. I think it can be USERSET but I wouldn't want to
>>> encourage users to see turning it off as a performance tuning feature.
>>> If the admin turns it on for the server, its on, so its SIGHUP.
>>>
>>> Any holes in that I haven't noticed?
>>
>> And of course, as soon as I wrote that I thought of the problem. We
>> mustn't make a write that hasn't been covered by a FPW, so we must
>> know ahead of time whether to WAL log hints or not. We can't simply
>> turn it on/off any longer, now that we have to WAL log hint bits also.
>> So thanks for making me think of that.
>>
>> We *could* make it turn on/off at each checkpoint, but its easier just
>> to say that it can be turned on/off at server start.
>
> Attached patch v6 now handles hint bits and checksums correctly,
> following Heikki's comments.
>
> In recovery, setting a hint doesn't dirty a block if it wasn't already
> dirty. So we can write some hints, and we can set others but not write
> them.
>
> Lots of comments in the code.


v7

* Fixes merge conflict
* Minor patch cleanups
* Adds checksum of complete page including hole
* Calcs checksum in mdwrite() so we pickup all non-shared buffer writes also

Robert mentioned to me there were outstanding concerns on this patch.
I know of none, and have double checked the thread to confirm all
concerns are fully addressed. Adding to CF.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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