diff --git a/.gitignore b/.gitignore
index 0da876b..7f6f58f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ logout
 .Rhistory
 .RData
 .Ruserdata
+replay_memory
diff --git a/DESCRIPTION b/DESCRIPTION
index 486c22b..608c0de 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -2,7 +2,10 @@ Package: rlR
 Type: Package
 Title: Reinforcement Learning in R
 Version: 0.1.0
-Authors@R: person("Xudong", "Sun", email = {"smilesun.east@gmail.com"}, role = c("aut", "cre"))
+Authors@R: c(
+    person("Xudong", "Sun", email = {"smilesun.east@gmail.com"}, role = c("aut", "cre")),
+    person("Sebastian", "Gruber", email = {"gruber_sebastian@t-online.de"}, role = c("ctb"))
+    )
 Maintainer: Xudong Sun <smilesun.east@gmail.com>
 Description: Reinforcement Learning with deep Q learning, double deep Q
     learning, frozen target deep Q learning, policy gradient deep learning, policy
@@ -21,6 +24,9 @@ Imports:
     logging,
     ggplot2,
     openssl,
+    RSQLite,
+    png,
+    stringr,
     magrittr,
     abind
 LazyData: true
diff --git a/R/replaymemdb.R b/R/replaymemdb.R
new file mode 100644
index 0000000..7d4a05a
--- /dev/null
+++ b/R/replaymemdb.R
@@ -0,0 +1,226 @@
+#' @importFrom magrittr %>% %<>%
+#FIXME:  RSQLite::dbDisconnect(agent$mem$db.con) run this at the end of try-catch-finally
+ReplayMemDB = R6::R6Class(
+  "ReplayMemDB",
+  inherit = ReplayMem,
+  public = list(
+    len = NULL,
+    replayed.idx = NULL,
+    conf = NULL,
+    agent = NULL,
+    db.con = NULL,
+    table.name = NULL,
+    initialize = function(agent, conf) {
+      # initialize sqlite connection
+      self$db.con = RSQLite::dbConnect(RSQLite::SQLite(), dbname = "replay_memory")    # RSQLite::SQLite() load the driver
+      # pick the env name as table name
+      self$table.name = agent$env$env %>%
+        stringr::str_extract("<([a-z]|[A-Z]|-|[0-9])*>") %>%    # remove the special signs
+        stringr::str_remove_all("<|>")   # there's maybe a better solution
+      # delete old replay table
+      RSQLite::dbExecute( self$db.con, paste0("DROP TABLE IF EXISTS '", self$table.name, "'") )
+      # manually create new table to specify primary key - this reduces index search complexity from O(n) to O(log n)
+      RSQLite::dbExecute( self$db.con, paste0("
+        CREATE TABLE '", self$table.name, "' (
+          state_id INTEGER PRIMARY KEY,
+          state_old TEXT,
+          reward NUMERIC,
+          action INTEGER,
+          state_new TEXT,
+          done INTEGER,
+          episode INTEGER,
+          stepidx INTEGER,
+          info TEXT )
+      ") )
+      self$len = 0L
+      self$conf = conf
+      self$agent = agent
+    },
+
+    reset = function() {
+      RSQLite::dbExecute( self$db.con, paste0("DROP TABLE '", self$table.name, "'") )
+      self$len = 0L
+    },
+
+    mkInst = function(state.old, action, reward, state.new, done, info) {
+      # transform/compress states into single string for DB entry
+      if (length(self$agent$state_dim) == 1) {
+        state.old %<>% paste(collapse = "_")
+        state.new %<>% paste(collapse = "_")
+      } else {
+        state.old = (state.old / 255L) %>% (png::writePNG) %>% paste(collapse = "")
+        state.new = (state.new / 255L) %>% (png::writePNG) %>% paste(collapse = "")
+      }
+      self$len = self$len + 1L
+      # don't use "." in column names - SQLite will throw up on it
+      data.frame(
+        state_id   = self$len,
+        #state.hash = digest(old_state, algo = "md5"),
+        state_old  = state.old,
+        reward     = reward,
+        action     = action,
+        state_new  = state.new,
+        done       = done,
+        episode    = info$episode,
+        stepidx    = info$stepidx,
+        info       = if (length(info$info)==0) "NULL" else info$info %>% as.character()
+      )
+    },
+
+    add = function(ins) {
+      # write to sqlite table
+      RSQLite::dbWriteTable( self$db.con, self$table.name, ins, append = TRUE)
+    },
+
+    afterEpisode = function(interact) {
+      # do nothing
+    },
+
+    afterStep = function() {
+      # do nothing
+    },
+
+    getSamples = function(idx) {
+
+      str_to_array = function(string) {
+
+        if (length(self$agent$state_dim) == 1) {   
+          # if order of tensor is only 1, which means flat linear state
+          strsplit(string, "_")[[1]] %>%     # self defined format of the string, now split it by spliter '_'
+            as.numeric() %>%
+            array()
+        } else if (length(self$agent$state_dim) %in% 2L:3L) {
+          change_storage = function(y) {
+            storage.mode(y) = "integer"  # change storage type to integer to save space
+            y
+          }
+          (  
+            # magittr  require ()
+            string %>%
+              strsplit("") %>%     # ABEF39 SPLIT into c("A", "B", "E", ...)
+              .[[1]] %>%    # return of split is a list
+              (function(x) paste0(x[c(TRUE, FALSE)], x[c(FALSE, TRUE)])) %>% #combine to pairs, equivalent to zip:    x[c(TRUE, FALSE)] takes the 1st,3st,5st  and x[c(FALSE, TRUE)] take the 2st, 4st
+              as.hexmode %>%   # necessary for correct as.raw. For R to understand this is hexcode other than String.
+              as.raw %>%       # make it readable as PNG
+              (png::readPNG) * 255   # png package assums image to have range 0-1
+          ) %>%
+          change_storage %>%    # float storage to int storage
+          array(dim = self$agent$state_dim) # this is necessary if state_dim has shape x1 x2 1
+          #FIXME: IS THE Orientation of the array right! Critically Important
+        }
+      }
+
+      replay.samples = paste0("
+          SELECT state_old, action, reward, state_new, done, info, episode, stepidx
+          FROM '", self$table.name, "'
+          WHERE state_id IN (", paste(idx, collapse = ", "), ")
+        ") %>%
+        RSQLite::dbGetQuery(conn = self$db.con)
+      # replay.samples now are the results from the query
+      lapply(1:nrow(replay.samples), function(i) list(
+        state.old = replay.samples$state_old[i] %>% str_to_array,
+        action    = replay.samples$action[i],
+        reward    = replay.samples$reward[i],
+        state.new = replay.samples$state_new[i] %>% str_to_array,
+        done      = replay.samples$done[i],
+        info      = list(
+          episode = replay.samples$episode[i],
+          stepidx = replay.samples$stepidx[i],
+          info    = replay.samples$info[i]
+        )
+      ))
+    }
+    ),
+  private = list(),
+  active = list()
+)
+
+
+ReplayMemUniformDB = R6::R6Class("ReplayMemUniformDB",
+  inherit = ReplayMemDB,
+  public = list(
+    sample.fun = function(k) {
+      k = min(k, self$len)
+      self$replayed.idx = sample(self$len)[1L:k]
+      list.res          = self$getSamples(self$replayed.idx)
+      return(list.res)
+    }
+  ),
+  private = list(),
+  active = list()
+  )
+
+
+ReplayMemPng = R6::R6Class(
+  "ReplayMemPng",
+  inherit = ReplayMemUniform,
+  public = list(
+    len = NULL,
+    replayed.idx = NULL,
+    conf = NULL,
+    agent = NULL,
+    table.name = NULL,
+    initialize = function(agent, conf) {
+      super$initialize(agent, conf)
+    },
+
+    mkInst = function(state.old, action, reward, state.new, done, info) {
+      # transform/compress states into single string for DB entry
+      if (length(self$agent$state_dim) == 1) {
+        state.old %<>% paste(collapse = "_")
+        state.new %<>% paste(collapse = "_")
+      } else {
+        state.old = (state.old / 255L) %>% (png::writePNG) %>% paste(collapse = "")
+        state.new = (state.new / 255L) %>% (png::writePNG) %>% paste(collapse = "")
+      }
+      super$mkInst(state.old, action, reward, state.new, done, info)
+    },
+
+    sample.fun = function(k) {
+      k = min(k, self$size)
+      #FIXME: the replayed.idx are not natural index, but just the position in the replay memory
+      self$replayed.idx = sample(self$size)[1L:k]
+      list.res = lapply(self$replayed.idx, function(x) self$samples[[x]])
+      replay.samples = list.res
+      # replay.samples now are the results from the query
+
+      #FIXME: IS THE Orientation of the array right! Critically Important
+      list.replay = lapply(replay.samples, function(x) list(
+        state.old = x$state.old %>% str_to_array_h %>% array(dim = self$agent$state_dim),
+        action    = x$action,
+        reward    = x$reward,
+        state.new = x$state.new %>% str_to_array_h %>% array(dim = self$agent$state_dim),
+        done      = x$done,
+        info      = list(
+          episode = x$episode,
+          stepidx = x$stepidx,
+          info    = x$info
+        )
+      ))
+      list.replay    # DEBUG: self$agent$env$showImage(list.replay[[64]][["state.new"]]) make sense
+    }
+    ),
+  private = list(),
+  active = list()
+)
+
+
+
+change_storage = function(y) {
+  storage.mode(y) = "integer"  # change storage type to integer to save space
+  y
+}
+
+str_to_array_h = function(string) {
+  (
+    # magittr  require ()
+    string %>%
+      strsplit("") %>%     # ABEF39 SPLIT into c("A", "B", "E", ...)
+      .[[1]] %>%    # return of split is a list
+        (function(x) paste0(x[c(TRUE, FALSE)], x[c(FALSE, TRUE)])) %>% #combine to pairs, equivalent to zip:    x[c(TRUE, FALSE)] takes the 1st,3st,5st  and x[c(FALSE, TRUE)] take the 2st, 4st
+          as.hexmode %>%   # necessary for correct as.raw. For R to understand this is hexcode other than String.
+            as.raw %>%       # make it readable as PNG
+              (png::readPNG) * 255   # png package assums image to have range 0-1
+      ) %>%
+  change_storage    # float storage to int storage
+}
diff --git a/tests/testthat/test_file_replay_mem_png.R b/tests/testthat/test_file_replay_mem_png.R
new file mode 100644
index 0000000..0f80998
--- /dev/null
+++ b/tests/testthat/test_file_replay_mem_png.R
@@ -0,0 +1,11 @@
+context("replay_mem")
+test_that("test basic replay_mem works", {
+env = makeGymEnv("Pong-v0")
+env$overview()
+conf = getDefaultConf("AgentDQN")
+conf$show()
+conf$set(render = T, console = T, replay.memname = "Png")
+agent = makeAgent("AgentDQN", env, conf)
+perf = agent$learn(1L)
+agent$plotPerf()
+})