Re: Re: Re:

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(at)sqlexec(dot)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.