Re: SSI patch version 14

On Tue, 2011-01-25 at 09:41 -0600, Kevin Grittner wrote:
> Yep. For the visual thinkers out there, the whole concept can be
> understood by looking at the jpeg file that's in the Wiki page:
>
> http://wiki.postgresql.org/images/e/eb/Serialization-Anomalies-in-Snapshot-Isolation.png

Yes, that helped a lot throughout the review process. Good job keeping
it up-to-date!

> Yes, that would work. It would lower one type of overhead a little
> and allow RO transactions to be released from SSI tracking earlier.
> The question is how to determine it without taking too much time
> scanning the finished transaction list for every active read write
> transaction every time you start a RO transaction. I don't think
> that it's a trivial enough issue to consider for 9.1; it's certainly
> one to put on the list to look at for 9.2.

It's OK to leave it to 9.2. But if it's a RO deferrable transaction,
it's just going to go to sleep in that case anyway; so why not look for
an opportunity to get a safe snapshot right away?

Regards,
Jeff Davis