Re: Global snapshots

From: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
To: Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Global snapshots
Date: 2018-05-02 02:58:37
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On 5/1/18 12:27, Stas Kelvich wrote:
> Clock-SI is described in [5] and here I provide a small overview, which
> supposedly should be enough to catch the idea. Assume that each node runs Commit
> Sequence Number (CSN) based visibility: database tracks one counter for each
> transaction start (xid) and another counter for each transaction commit (csn).
> In such setting, a snapshot is just a single number -- a copy of current CSN at
> the moment when the snapshot was taken. Visibility rules are boiled down to
> checking whether current tuple's CSN is less than our snapshot's csn. Also it
> worth of mentioning that for the last 5 years there is an active proposal to
> switch Postgres to CSN-based visibility [6].

But that proposal has so far not succeeded. How are you overcoming the
reasons for that?

Peter Eisentraut
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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