Implementing RESET CONNECTION ...

We have implemented a patch which can be used by connection pools for
instance.
RESECT CONNECTION cleans up a backend so that it can be reused.
Temp tables, LISTEN / NOTIFY stuff, WITH HOLD cursors, open
transactions, prepared statements and GUCs are cleaned up.
I hope we have not missed important per-backend information.

test=# BEGIN;
BEGIN
test=# RESET CONNECTION;
RESET
test=# COMMIT;
WARNING: there is no transaction in progress
COMMIT
test=# PREPARE myplan(int, int) AS SELECT $1 + $2;
PREPARE
test=# RESET CONNECTION;
RESET
test=# EXECUTE myplan(1, 2);
ERROR: prepared statement "myplan" does not exist
test=#
test=# DECLARE mycur CURSOR WITH HOLD FOR SELECT relname FROM pg_class;
DECLARE CURSOR
test=# FETCH NEXT FROM mycur;
relname
---------
views
(1 row)

test=# RESET CONNECTION;
RESET
test=# FETCH NEXT FROM mycur;
ERROR: cursor "mycur" does not exist
test=# CREATE TEMP TABLE mytmp (id int4);
CREATE TABLE
test=# RESET CONNECTION;
RESET
test=# INSERT INTO mytmp VALUES (10);
ERROR: relation "mytmp" does not exist

All regression tests passed.
It would be nice if we had this in 8.1.

Best regards,

Hans

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