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

Hi,

I'm posting a v4-0001 patch for the new functions
postgres_fdw_get_connections() and postgres_fdw_disconnect().  In this
patch, I tried to address the review comments provided upthread.

At a high level, the changes include:
1) Storing the foreign server id in the cache entry which will help to
fetch the server name associated with it easily.
2) postgres_fdw_get_connections now returns an open connection server
name and true or false to indicate whether it's valid or not.
3) postgres_fdw_get_connections can issue a warning when the cache
look up for server name returns null i.e. the foreign server is
dropped. Please see the comments before postgres_fdw_get_connections
in which situations this is possible.
4) postgres_fdw_disconnect('myserver') disconnects the open connection
only when it's not being used in the current xact. If it's used, then
false is returned and a warning is issued.
5) postgres_fdw_disconnect() disconnects all the connections only when
they are not being used in the current xact. If at least one
connection that's being used exists, then it issues a warning and
returns true if at least one open connection gets closed otherwise
false. If there are no connections made yet or connection cache is
empty, then also false is returned.
6) postgres_fdw_disconnect can discard the entire cache if there is no
active connection.

Thoughts?

Below things are still pending which I plan to post new patches after
the v4-0001 is reviewed:
1) changing the version of postgres_fdw--1.0.sql to postgres_fdw--1.1.sql
2) 0002 and 0003 patches having keep_connections GUC and
keep_connection server level option.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com