Re: Is it really difficult for postgres_fdw to implement READ COMMITTED isolation?

On Tue, Sep 18, 2018 at 8:28 PM Jinhua Luo <luajit(dot)io(at)gmail(dot)com> wrote:

>
> https://www.postgresql.org/docs/current/static/postgres-fdw.html#id-1.11.7.43.12
>
> As the doc said, the REPEATABLE READ isolation level is used to get
> snapshot-consistent results.
>
> But is it possible that postgres_fdw could get to know which remote
> queries involved by each top outer command in the local transaction,
> and use the same snapshot in the remote server to execute them
> sequentially? For example, could we use PREPARE TRANSACTION and SET
> TRANSACTION SNAPSHOT to archive this goal? Then we could use READ
> COMMITTED on both sides?
>
>
I guess the problem is 1. exporting snapshots is not cheap 2. tracking
prepared transactions is not implemented. See a nearby thread on
"transaction involving multiple foreign server".

--
Best Wishes,
Ashutosh Bapat