Re: Proposal for CSN based snapshots

On Mon, May 12, 2014 at 4:56 PM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> On 01/24/2014 02:10 PM, Rajeev rastogi wrote:
>>
>> We are also planning to implement CSN based snapshot.
>> So I am curious to know whether any further development is happening on
>> this.
>
>
> I started looking into this, and plan to work on this for 9.5. It's a big
> project, so any help is welcome. The design I have in mind is to use the LSN
> of the commit record as the CSN (as Greg Stark suggested).

I did do some coding work on this, but the free time I used to work on
this basically disappeared with a child in the family. I guess what I
have has bitrotted beyond recognition. However I may still have some
insight that may be of use.

From your comments I presume that you are going with the original,
simpler approach proposed by Robert to simply keep the XID-CSN map
around for ever and probe it for all visibility lookups that lie
outside of the xmin-xmax range? As opposed to the more complex hybrid
approach I proposed that keeps a short term XID-CSN map and lazily
builds conventional list-of-concurrent-XIDs snapshots for long lived
snapshots. I think that would be prudent, as the simpler approach
needs mostly the same ground work and if turns out to work well
enough, simpler is always better.

Regards,
Ants Aasma
--
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de