From: MichaelDBA <MichaelDBA@sqlexec.com>
To: Simon Riggs <simon.riggs@enterprisedb.com>
Cc: Holger Jakobs <holger@jakobs.com>
Cc: pgsql-admin@lists.postgresql.org, Firthouse banu <penguinsfairy@gmail.com>
Cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: Re: Re:
Date: Wed, 24 Nov 2021 13:18:40 -0500
Message-ID: <77723597-904d-bdae-730a-752a6e4af7e0@sqlexec.com> (raw)
In-Reply-To: <CANbhV-FLDLmYnAGPNMkpqU1S-Yx2wPQyBhpf3HQbQ0TxATVceA@mail.gmail.com>
References: <CAK_Ha4yABYGEGAMzfNJaxeepeQNFRTFaqYRsns3GCPFeQWEWhQ@mail.gmail.com>
<6cb32d43-75d1-b896-5267-48d75c536808@sqlexec.com>
<CANbhV-G7piJpocze7Hu+NEUb5omzc59PxgyYmX0PSwsSZznvrA@mail.gmail.com>
<0ED6B91F-C228-404F-A4F2-B9532E205B2D@jakobs.com>
<7713c1fd-c674-eb79-02ea-0daf749ac098@sqlexec.com>
<CANbhV-FLDLmYnAGPNMkpqU1S-Yx2wPQyBhpf3HQbQ0TxATVceA@mail.gmail.com>
Thanks, Simon, for your continued feedback.
Simon Riggs wrote on 11/24/2021 12:49 PM:
> On Wed, 24 Nov 2021 at 17:38, MichaelDBA <MichaelDBA@sqlexec.com> wrote:
>> Oh really? BDR is acid-compliant? How can it be without a global lock manager to control access to resources and a consistent view of data and enforce isolation levels?
> Many types of distributed system offer consistency. Very few use a
> global lock manager, so this is not a requirement.
Let me try to state it another way... Without a central place where you
can see all the SQL coming against all of the read-write PG nodes at the
same time, you cannot avoid conflicts. PG is active/passive so it
cannot resolve conflicts across multiple primary PG clusters. Hence,
BDR offers an "underneath the covers" approach to deal with conflicts
when they do arise, but innevitably a conflict causes a previous commit
to be rolled back or "suspended" for some kind of manual intervention
later. That is why BDR nowhere states that BDR is ACID-compliant. If it
were ACID-compliant, there would be no external need to address SQL
conflicts.
>> Please explain the magic.
> Anyone interested to know more can start here:
> https://www.enterprisedb.com/products/bidirectional-replication-bdr-postgresql-database
>
I spent about 15 minutes starting at the URL stated above to drill down
into some areas where this subject might be addressed and I couldn't
find it. Perhaps you could be more specific.
I did find this in separate BDR documentation: "BDRis a loosely coupled
shared-nothing multi-master design." I guess you can say "loosely
coupled" is a nice way to say not ACID-compliant.
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