Re: Transactions involving multiple postgres foreign servers

On Thu, Oct 26, 2017 at 7:41 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> Because I don't want to break the current user semantics. that is,
> currently it's guaranteed that the subsequent reads can see the
> committed result of previous writes even if the previous transactions
> were distributed transactions. And it's ensured by writer side. If we
> can make the reader side ensure it, the backend process don't need to
> wait for the resolver process.
>
> The waiting backend process are released by resolver process after the
> resolver process tried to resolve foreign transactions. Even if
> resolver process failed to either connect to foreign server or to
> resolve foreign transaction the backend process will be released and
> the foreign transactions are leaved as dangling transaction in that
> case, which are processed later. Also if resolver process takes a long
> time to resolve foreign transactions for whatever reason the user can
> cancel it by Ctl-c anytime.
>

So, there's no guarantee that the next command issued from the
connection *will* see the committed data, since the foreign
transaction might not have committed because of a network glitch
(say). If we go this route of making backends wait for resolver to
resolve the foreign transaction, we will have add complexity to make
sure that the waiting backends are woken up in problematic events like
crash of the resolver process OR if the resolver process hangs in a
connection to a foreign server etc. I am not sure that the complexity
is worth the half-guarantee.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company