On Thu, Jun 18, 2020 at 04:09:56PM +0530, Amit Kapila wrote:
> You are right and we are not going to claim that after this feature is
> committed. This feature has independent use cases like it can allow
> parallel copy when foreign tables are involved once we have parallel
> copy and surely there will be more. I think it is clear that we need
> atomic visibility (some way to ensure global consistency) to avoid the
> data inconsistency problems you and I are worried about and we can do
> that as a separate patch but at this stage, it would be good if we can
> have some high-level design of that as well so that if we need some
> adjustments in the design/implementation of this patch then we can do
> it now. I think there is some discussion on the other threads (like
> [1]) about the kind of stuff we are worried about which I need to
> follow up on to study the impact.
>
> Having said that, I don't think that is a reason to stop reviewing or
> working on this patch.
I think our first step is to allow sharding to work on read-only
databases, e.g. data warehousing. Read/write will require global
snapshots. It is true that 2PC is limited usefulness without global
snapshots, because, by definition, systems using 2PC are read-write
systems. However, I can see cases where you are loading data into a
data warehouse but want 2PC so the systems remain consistent even if
there is a crash during loading.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee