On 2020-12-30 17:59, Bharath Rupireddy wrote:
On Wed, Dec 30, 2020 at 5:20 PM Alexey Kondratov
<a.kondra...@postgrespro.ru> wrote:
On 2020-12-30 09:10, Bharath Rupireddy wrote:
I still have some doubts that it is worth of allowing to call
postgres_fdw_disconnect() in the explicit transaction block, since it
adds a lot of things to care and check for. But otherwise current
logic
looks solid.
+ errdetail("Such connections get
closed either in the next use or
at the end of the current transaction.")
+ : errdetail("Such connection gets
closed either in the next use or
at the end of the current transaction.")));
Does it really have a chance to get closed on the next use? If foreign
server is dropped then user mapping should be dropped as well (either
with CASCADE or manually), but we do need user mapping for a local
cache
lookup. That way, if I understand all the discussion up-thread
correctly, we can only close such connections at the end of xact, do
we?
The next use of such a connection in the following query whose foreign
server would have been dropped fails because of the cascading that can
happen to drop the user mapping and the foreign table as well. During
the start of the next query such connection will be marked as
invalidated because xact_depth of that connection is > 1 and when the
fail happens, txn gets aborted due to which pgfdw_xact_callback gets
called and in that the connection gets closed. To make it more clear,
please have a look at the scenarios [1].
In my understanding 'connection gets closed either in the next use'
means that connection will be closed next time someone will try to use
it, i.e. GetConnection() will be called and it closes this connection
because of a bad state. However, if foreign server is dropped
GetConnection() cannot lookup the connection because it needs a user
mapping oid as a key.
I had a look on your scenarios. IIUC, under **next use** you mean a
select attempt from a table belonging to the same foreign server, which
leads to a transaction abort and connection gets closed in the xact
callback. Sorry, maybe I am missing something, but this just confirms
that such connections only get closed in the xact callback (taking into
account your recently committed patch [1]), so 'next use' looks
misleading.
[1]
https://www.postgresql.org/message-id/8b2aa1aa-c638-12a8-cb56-ea0f0a5019cf%40oss.nttdata.com
Regards
--
Alexey Kondratov
Postgres Professional https://www.postgrespro.com
Russian Postgres Company
