we should also rethink replication on the presence database which is the majority source of constant writes (and O(n) size of env). from op log 

{ "ts" : Timestamp(1405780166, 2), "h" : NumberLong("7248998997472728194"), "v" : 2, "op" : "u", "ns" : "juju.stateServers", "o2" : { "_id" : "apiHostPorts" }, "o" : { "$set" : { "txn-queue.0" : "53ca80c6ac02cd3e930005cc_14963302" } } }
{ "ts" : Timestamp(1405780166, 3), "h" : NumberLong("-5418504314646616294"), "v" : 2, "op" : "u", "ns" : "juju.txns", "o2" : { "_id" : ObjectId("53ca80c6ac02cd3e930005cc") }, "o" : { "$set" : { "n" : "14963302", "s" : 2 } } }
{ "ts" : Timestamp(1405780166, 4), "h" : NumberLong("7570052371187181427"), "v" : 2, "op" : "u", "ns" : "juju.txns", "o2" : { "_id" : ObjectId("53ca80c6ac02cd3e930005cc") }, "o" : { "$set" : { "r" : [  NumberLong(67) ], "s" : 4 } } }
{ "ts" : Timestamp(1405780166, 5), "h" : NumberLong("8591084146477772223"), "v" : 2, "op" : "u", "ns" : "juju.stateServers", "o2" : { "_id" : "apiHostPorts" }, "o" : { "$set" : { "apihostports" : [   [       {   "value" : "pbdpm.cluster.mallards",      "addresstype" : "hostname",     "networkscope" : "public",      "port" : 17070 },       {       "value" : "192.168.9.74",       "addresstype" : "ipv4",         "networkscope" : "local-cloud",      "port" : 17070 },       {       "value" : "127.0.0.1",  "addresstype" : "ipv4",         "networkscope" : "local-machine",       "port" : 17070 },       {       "value" : "::1",        "addresstype" : "ipv6",      "networkscope" : "local-machine",       "port" : 17070 },       {       "value" : "fe80::225:90ff:fe4c:e79e",   "addresstype" : "ipv6",         "port" : 17070 } ] ], "txn-queue" : [ ], "txn-revno" : NumberLong(68) } } }
{ "ts" : Timestamp(1405780166, 6), "h" : NumberLong("-4967417421360925452"), "v" : 2, "op" : "i", "ns" : "juju.txns.log", "o" : { "_id" : ObjectId("53ca80c6ac02cd3e930005cc"), "stateServers" : { "d" : [  "apiHostPorts" ], "r" : [  NumberLong(68) ] } } }
Type "it" for more
juju:PRIMARY> it
{ "ts" : Timestamp(1405780167, 1), "h" : NumberLong("-2430360262590208338"), "v" : 2, "op" : "u", "ns" : "juju.txns", "o2" : { "_id" : ObjectId("53ca80c6ac02cd3e930005cc") }, "o" : { "$set" : { "s" : 6 } } }
{ "ts" : Timestamp(1405780168, 1), "h" : NumberLong("2892245837688454076"), "v" : 2, "op" : "i", "ns" : "presence.presence.pings", "o" : { "_id" : NumberLong(1405780170), "alive" : { "1" : NumberLong("4294967296") } } }
{ "ts" : Timestamp(1405780169, 1), "h" : NumberLong("-4920408163957595002"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.0" : NumberLong("9007199254740992") } } }
{ "ts" : Timestamp(1405780169, 2), "h" : NumberLong("-8421208321601717803"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.1" : NumberLong("5368709120") } } }
{ "ts" : Timestamp(1405780170, 1), "h" : NumberLong("-1730416142908418047"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.1" : NumberLong("5372903424") } } }
{ "ts" : Timestamp(1405780170, 2), "h" : NumberLong("-6305445750247567146"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.1" : NumberLong("5372903440") } } }
{ "ts" : Timestamp(1405780170, 3), "h" : NumberLong("6153091466849433046"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.1" : NumberLong("70374117081104") } } }
{ "ts" : Timestamp(1405780171, 1), "h" : NumberLong("7412387155717674164"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.0" : NumberLong("9042383626829824") } } }
{ "ts" : Timestamp(1405780171, 2), "h" : NumberLong("7958787061438798335"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.1" : NumberLong("70923872894992") } } }
{ "ts" : Timestamp(1405780171, 3), "h" : NumberLong("7306268237551920513"), "v" : 2, "op" : "u", "ns" : "presence.presence.pings", "o2" : { "_id" : NumberLong(1405780170) }, "o" : { "$set" : { "alive.0" : NumberLong("9042383626829856") } } }