Re: serializable anomaly - duplicate primary keys

Hi,

> The root cause is that unique checks use a dirty snapshot. They can
> decide a key is unused because of a deletion the transaction cannot
> see. The fix might be to ask our own snapshot the same question, and
> fail if it still sees the key in use. I don't think this will require
> an ABI change.

I prepared a PoC patch that shows how this could be archived. Also it
includes regression tests for everything discussed above.

One drawback I discovered is that the patch introduces a
false-positive conflict detection that causes the existing
partition-key-update-3.spec to fail. I'm not 100% certain what to do
about it. Given the fact that SSI generally has false-positives, maybe
we should just rewrite the test? This seems to be better compared to
what we currently have and personally I don't have better proposals at
the moment.

Thoughts?

--
Best regards,
Aleksander Alekseev