Make cassandra connection pool size configurable.

r2/example.ini

@@ -117,6 +117,8 @@ rendercaches = 127.0.0.1:11211
 permacache_memcaches = 127.0.0.1:11211
 # cassandra hosts. one of these will be chosen at random by pycassa
 cassandra_seeds = 127.0.0.1:9160
+# number of connections to keep open to the cassandra ring
+cassandra_pool_size = 5
 # read/write consistency levels for Cassandra
 cassandra_rcl = ONE
 cassandra_wcl = ONE

r2/r2/lib/app_globals.py

@@ -69,6 +69,7 @@ class Globals(object):
                  'comment_visits_period',
                   'min_membership_create_community',
                  'bcrypt_work_factor',
+                 'cassandra_pool_size',
                  ]
 
     float_props = ['min_promote_bid',
@@ -236,7 +237,7 @@ class Globals(object):
                     stats=self.stats,
                     logging_name="main",
                     server_list=self.cassandra_seeds,
-                    pool_size=len(self.cassandra_seeds),
+                    pool_size=self.cassandra_pool_size,
                     timeout=2,
                     max_retries=3,
                     prefill=False