Re: [PATCH] postgres_fdw connection caching - cause remote sessions linger till the local session exit

On Wed, Jul 1, 2020 at 3:54 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:

> If we were to use idle_session_timeout (from patch [1]) for the remote
> session to go off without
> having to delete the corresponding entry from local connection cache and
> after that if we submit foreign query from local session, then below
> error would occur,
> which may not be an expected behaviour. (I took the patch from [1] and
> intentionally set the
> idle_session_timeout to a low value on remote server, issued a
> foreign_tbl query which
> caused remote session to open and after idle_session_timeout , the
> remote session
> closes and now issue the foreign_tbl query from local session)
>
> postgres=# SELECT * FROM foreign_tbl;
> ERROR: server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> CONTEXT: remote SQL command: START TRANSACTION ISOLATION LEVEL REPEATABLE READ
> postgres=#

This is actually strange. AFAIR the code, without looking at the
current code, when a query picks a foreign connection it checks its
state. It's possible that the connection has not been marked bad by
the time you fire new query. If the problem exists probably we should
fix it anyway since the backend at the other end of the connection has
higher chances of being killed while the connection was sitting idle
in the cache.

--
Best Wishes,
Ashutosh Bapat