Re: POC and rebased patch for CSN based snapshots

From: "movead(dot)li(at)highgo(dot)ca" <movead(dot)li(at)highgo(dot)ca>
To: "Andrey V(dot) Lepikhov" <a(dot)lepikhov(at)postgrespro(dot)ru>
Cc: pgsql-hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Amit Kapila" <amit(dot)kapila16(at)gmail(dot)com>
Subject: Re: POC and rebased patch for CSN based snapshots
Date: 2020-07-13 06:46:23
Message-ID: 2020071314462009503617@highgo.ca
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>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.
Sorry, I think this is my wrong understand about Clock-SI. At first I expect
we can get a absolutly snapshot, for example B should not include in the
snapshot because it happened after time t1. How ever Clock-SI can not guarantee
that and no design guarantee that at all.

Regards,
Highgo Software (Canada/China/Pakistan)
URL : www.highgo.ca
EMAIL: mailto:movead(dot)li(at)highgo(dot)ca

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