Re: Enabling Checksums

On Mon, Apr 22, 2013 at 10:57 PM, Ants Aasma <ants(at)cybertec(dot)at> wrote:
> On Mon, Apr 22, 2013 at 10:54 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> On 22 April 2013 20:32, Florian Pflug <fgp(at)phlo(dot)org> wrote:
>>
>>> Assuming that we only ship a plain C implementation with 9.3, what
>>> are we missing on that front? The C implementation of FNV1+SHIFT is
>>> only a few dozen lines or so.
>>
>> Forgive me, I can't seem to locate the patch for this? Re-post please,
>> just for clarity.
>
> Not posted yet. I'm writing it as we speak. Will post within half an hour or so.

A slight delay, but here it is. I didn't lift the checksum part into a
separate file as I didn't have a great idea what I would call it. The
code is reasonably compact so I don't see a great need for this right
now. It would be more worth the effort when/if we add non-generic
variants. I'm not particularly attached to the method I used to mask
out pd_checksum field, this could be improved if someone has a better
idea how to structure the code.

I confirmed with objdump that compiling on GCC 4.7 with -msse4.1
-funroll-loops -ftree-vectorize does in fact vectorize that loop.
Simple way to verify: objdump -d src/backend/storage/page/bufpage.o |
grep pmulld | wc -l should output 16.

Unfortunately I can't work on this patch for about a week. Postgresql
9.3 will have to wait for me as I need to tend to the release of Ants
v2.0.

Regards,
Ants Aasma
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