diff --git a/.travis.yml b/.travis.yml
index 900dae0..e876d86 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,12 +4,12 @@ env: LUA_PATH="./?/init.lua;./?.lua"
 before_install:
   - sudo apt-get update -qq
   - sudo apt-get install -y screen lua5.2 liblua5.2-dev libboost-filesystem-dev libboost-filesystem-dev libboost-thread-dev libssl-dev
-  - wget https://github.com/mongodb/mongo-cxx-driver/archive/legacy-0.9.0.tar.gz
-  - tar zxvf legacy-0.9.0.tar.gz
-  - cd mongo-cxx-driver-legacy-0.9.0 && sudo scons --prefix=/usr install-mongoclient && cd -
-  - wget https://github.com/moai/luamongo/archive/v0.4.3.tar.gz
-  - tar zxvf v0.4.3.tar.gz
-  - cd luamongo-0.4.3 && make && sudo mkdir -p /usr/lib/lua/5.2 && sudo cp mongo.so /usr/lib/lua/5.2 && cd -
+  - wget https://github.com/mongodb/mongo-cxx-driver/archive/legacy-1.1.0.tar.gz
+  - tar zxvf legacy-1.1.0.tar.gz
+  - cd mongo-cxx-driver-legacy-1.1.0 && sudo scons --sharedclient=yes --prefix=/usr install && cd -
+  - wget https://github.com/moai/luamongo/archive/v0.5.0.tar.gz
+  - tar zxvf v0.5.0.tar.gz
+  - cd luamongo-0.5.0 && make && sudo mkdir -p /usr/lib/lua/5.2 && sudo cp mongo.so /usr/lib/lua/5.2 && cd -
   - ssh-keygen -b 2048 -f /home/travis/.ssh/id_rsa -t rsa -q -N ""
   - ssh-keyscan -t rsa localhost > ~/.ssh/known_hosts
   - ssh-keyscan -t rsa $(hostname) >> ~/.ssh/known_hosts
diff --git a/mapreduce/cnn.lua b/mapreduce/cnn.lua
index cb2b1de..2ddec9c 100644
--- a/mapreduce/cnn.lua
+++ b/mapreduce/cnn.lua
@@ -44,8 +44,15 @@ function cnn:gridfs()
   return gridfs
 end
 
+-- this weak table allow to index gridfs objects using weak grid_file_builder
+-- keys
+local gridfs_instances = setmetatable({}, { __mode="k" })
+
 function cnn:grid_file_builder()
-  return mongo.GridFileBuilder.New(self:connect(), self.gridfs_dbname)
+  local gridfs = self:gridfs()
+  local grid_file_builder = mongo.GridFileBuilder.New(gridfs)
+  gridfs_instances[grid_file_builder] = gridfs
+  return grid_file_builder
 end
 
 function cnn:get_dbname()
diff --git a/mapreduce/examples/APRIL-ANN/common.lua b/mapreduce/examples/APRIL-ANN/common.lua
index fa3cc67..d583ba9 100644
--- a/mapreduce/examples/APRIL-ANN/common.lua
+++ b/mapreduce/examples/APRIL-ANN/common.lua
@@ -23,13 +23,13 @@ util.omp_set_num_threads(1)
 
 local serialize_to_gridfs = function(gridfs, filename, obj)
   gridfs:remove_file(filename)
-  local builder = mongo.GridFileBuilder.New(db, dbname)
+  local builder = mongo.GridFileBuilder.New(gridfs)
   builder:append(util.serialize(obj))
   builder:build(filename)
 end
 
 local deserialize_from_gridfs = function(gridfs, filename)
-  local file = assert( gridfs:find_file(filename) )
+  local file = assert( gridfs:find_file_by_name(filename) )
   local str_tbl = {}
   for i=1,file:num_chunks() do
     local chunk = file:chunk(i-1)
diff --git a/mapreduce/server.lua b/mapreduce/server.lua
index 41b0cf6..df4274b 100644
--- a/mapreduce/server.lua
+++ b/mapreduce/server.lua
@@ -333,7 +333,9 @@ local function server_drop_collections(self)
   local dbname = self.cnn:get_dbname()
   -- drop all the collections
   for _,name in ipairs(db:get_collections(dbname)) do
-    db:drop_collection(name)
+    if name ~= "system_indexes" then
+      db:drop_collection(dbname .. "." .. name)
+    end
   end
   local gridfs = self.cnn:gridfs()
   local list = gridfs:list()
diff --git a/mapreduce/utils.lua b/mapreduce/utils.lua
index 386da63..3b59db2 100644
--- a/mapreduce/utils.lua
+++ b/mapreduce/utils.lua
@@ -131,7 +131,7 @@ end
 -- and last chunks where the line is contained, and the first and last position
 -- inside the corresponding chunks
 local function gridfs_lines_iterator(gridfs, filename)
-  local gridfile      = gridfs:find_file(filename)
+  local gridfile      = assert( gridfs:find_file_by_name(filename) )
   local size          = #gridfile
   local current_chunk = 0
   local current_pos   = 1
diff --git a/test.sh b/test.sh
index 80b9364..c7863b9 100755
--- a/test.sh
+++ b/test.sh
@@ -6,7 +6,7 @@ if [[ $? -ne 0 ]]; then
     exit 1
 fi
 for storage in gridfs shared sshfs; do
-    ## COMBINER + ASSOCIATIVE COMMUTATIVE IDEMPOTENT REDUCER
+    echo COMBINER + ASSOCIATIVE COMMUTATIVE IDEMPOTENT REDUCER
     screen -d -m ./execute_example_worker.sh
     diff <(./execute_example_server.sh $storage | awk '{ print $1,$2 }' | sort) \
         <(cat mapreduce/server.lua \
@@ -17,7 +17,7 @@ for storage in gridfs shared sshfs; do
         echo "ERROR"
         exit 1
     fi
-    ## NO COMBINER + ASSOCIATIVE COMMUTATIVE IDEMPOTENT REDUCER
+    echo NO COMBINER + ASSOCIATIVE COMMUTATIVE IDEMPOTENT REDUCER
     screen -d -m ./execute_example_worker.sh
     diff <(lua execute_server.lua localhost wordcount \
         mapreduce.examples.WordCount.taskfn \
@@ -34,7 +34,7 @@ for storage in gridfs shared sshfs; do
         echo "ERROR"
         exit 1
     fi
-    ## NO COMBINER + GENERAL REDUCER
+    echo NO COMBINER + GENERAL REDUCER
     screen -d -m ./execute_example_worker.sh
     diff <(lua execute_server.lua localhost wordcount \
         mapreduce.examples.WordCount.taskfn \
@@ -51,7 +51,7 @@ for storage in gridfs shared sshfs; do
         echo "ERROR"
         exit 1
     fi
-    ## INIT SCRIPT
+    echo INIT SCRIPT
     screen -d -m ./execute_example_worker.sh
     diff <(lua execute_server.lua localhost wordcount \
         mapreduce.examples.WordCount \