Re: POC and rebased patch for CSN based snapshots

On 7/4/20 7:56 PM, movead(dot)li(at)highgo(dot)ca wrote:
>
>
> As far as I know about Clock-SI, left part of the blue line will
> setup as a snapshot
>
> if master require a snapshot at time t1. But in fact data A should
> in snapshot but
>
> not and data B should out of snapshot but not.
>
>
> If this scene may appear in your origin patch? Or something my
> understand about
>
> Clock-SI is wrong?
>
>
>

Sorry for late answer.

I have doubts that I fully understood your question, but still.
What real problems do you see here? Transaction t1 doesn't get state of
shard2 until time at node with shard2 won't reach start time of t1.
If transaction, that inserted B wants to know about it position in time
relatively to t1 it will generate CSN, attach to node1 and will see,
that t1 is not started yet.

Maybe you are saying about the case that someone who has a faster data
channel can use the knowledge from node1 to change the state at node2?
If so, i think it is not a problem, or you can explain your idea.

--
regards,
Andrey Lepikhov
Postgres Professional