Fix connection management bug when columns = *.

Instead of opening a connection per section and leaving it open until the
end for the run, open a connection just for getting this section columns
then close it. Per gripes from a user dealing with 90000 sections.

pgloader/db.py

@@ -148,7 +148,12 @@ ORDER BY attnum
 """
         self.log.debug("get_all_columns: %s %s %s" % (tablename, schemaname, sql))
 
-        columns = []        
+        columns = []
+
+        have_to_connect = self.dbconn is None
+        if have_to_connect:
+            self.reset()
+            
         cursor  = self.dbconn.cursor()
         try:
             cursor.execute(sql, [tablename, schemaname])
@@ -161,6 +166,9 @@ ORDER BY attnum
 
         cursor.close()
 
+        if have_to_connect:
+            self.close()
+
         return columns
 
     def reset(self):

pgloader/pgloader.py

@@ -314,8 +314,7 @@ class PGLoader(threading.Thread):
                 self.all_cols    = True
                 self.db.all_cols = True
 
-                # force db to connect now
-                self.db.reset()
+                # get column list from database
                 self.columns = self.db.get_all_columns(self.table)
                 self.log.info("columns = *, got %s", str(self.columns))