diff --git a/src/nanotron/data/petagraph_dataset.py b/src/nanotron/data/petagraph_dataset.py
index 4af72fe9..4ffaef62 100644
--- a/src/nanotron/data/petagraph_dataset.py
+++ b/src/nanotron/data/petagraph_dataset.py
@@ -6,7 +6,7 @@
 #
 # =============================================================================
 from torchdata.datapipes.iter import IterableWrapper, S3FileLoader, \
-    FileOpener, Mapper, StreamReader, FSSpecFileOpener, Prefetcher
+    FileOpener, Mapper, StreamReader, FSSpecFileOpener, Prefetcher, Shuffler
 
 from functools import partial
 import logging
@@ -37,10 +37,24 @@ def cyclic_iter(iter):
             yield x
 
 
+# =============================================================================
+# Constants
+# =============================================================================
+KMER_LENGTH = 31 # overlap
+
 # =============================================================================
 # Dataset class
 # =============================================================================
 class PetaGraphStreamDataset(torch.utils.data.IterableDataset):
+    """Training dataset to stream from Logan
+    
+    Parameters
+    ----------
+    sampling_seq_len_inflection : int
+        The sequence length at which to switch from sampling to keeping the sequence
+        below the inflection point we only keep the sequence with a probability pr
+        to its length. Above the inflection point we always keep the sequence.
+    """
 
     def __init__(self, 
         logger,
@@ -56,13 +70,15 @@ def __init__(self,
         prefetch_fasta_parsing: int = 10,
         log_directory: Path = None,
         rank: int = 0,
-        packed: bool = False
+        packed: bool = False,
+        sampling_seq_len_inflection: int = 1024
     ):
 
         self.samples_per_epoch = samples_per_epoch
         self.maxlen = maxlen
         self.create_attention_mask = create_attention_mask
         self.debug = debug
+        self.sampling_seq_len_inflection = sampling_seq_len_inflection
 
         self.logger = logger
         self.logging_func = partial(log_rank, logger=logger, level=logging.INFO, rank=0)
@@ -168,8 +184,12 @@ def __init__(self,
         sequences_unbatched = sequences_batched.unbatch()
         self.prefetch_sequences = prefetch_sequences
         if self.prefetch_sequences > 0:
-            self.logging_func(f"Prefetching {self.prefetch_sequences} unbatched sequences")
-            sequences_unbatched = sequences_unbatched.prefetch(self.prefetch_sequences)
+
+            # self.logging_func(f"Prefetching {self.prefetch_sequences} unbatched sequences")
+            # sequences_unbatched = sequences_unbatched.prefetch(self.prefetch_sequences)
+
+            self.logging_func(f"Prefetching and shuffling {self.prefetch_sequences} unbatched sequences")
+            sequences_unbatched = Shuffler(sequences_unbatched, buffer_size=self.prefetch_sequences)
 
         # sequences_crop = Mapper(sequences_unbatched, self.crop_maxlen)
         # sequences_tokenized = Mapper(sequences_crop, self.tokenize_and_pad)
@@ -221,7 +241,14 @@ def load_restart_consumed_files(restart_file: Path):
 
         return latest_epoch, latest_files
 
-    def decompression_func(self, input_data):
+    def decompression_func(self, input_data: Tuple[str, bytes]):
+        """Decompress the data
+
+        Parameters
+        ----------
+        input_data : Tuple[str, bytes]
+            The path and the data to decompress
+        """
         path, data = input_data
         try:
             dctx = zstandard.ZstdDecompressor()
@@ -231,8 +258,49 @@ def decompression_func(self, input_data):
             return path, None
 
         return path, decompressed_data
+    
+    def chop_at_first_repeated_kmer(sequence: str, k: int):
+        """Chop the sequence at the first repeated kmer
+        
+        Python implementation of:
+        https://gitlab.pasteur.fr/rchikhi_pasteur/logan-circles/-/blob/master/fix_repeated_31kmers.cpp?ref_type=heads
 
-    def fasta_parsing_func(self, input_data):
+        Parameters
+        ----------
+        sequence : str
+            The sequence to chop
+        k : int
+            The kmer length
+        """
+        kmers = set()
+        for i in range(len(sequence) - k + 1):
+            kmer = sequence[i:i+k]
+            if kmer in kmers:
+                return sequence[:i + k - 1]
+            kmers.add(kmer)
+        return sequence
+    
+
+    def length_sampling_filter(self, sequence: str) -> bool:
+        seq_len = len(sequence)
+        if seq_len >= self.sampling_seq_len_inflection:
+            return True
+        else:
+            prob = np.random.rand()
+            if prob < (seq_len / self.sampling_seq_len_inflection):
+                True
+
+        return False
+
+
+    def fasta_parsing_func(self, input_data: Tuple[str, bytes]):
+        """Parse the fasta data and return the sequences
+        
+        Parameters
+        ----------
+        input_data : Tuple[str, bytes]
+            The path and the data to parse
+        """
         path, data = input_data
         if data is None:
             return [[]]
@@ -241,7 +309,16 @@ def fasta_parsing_func(self, input_data):
         decoded_lines = data.decode()
         sequences = [(path, str(s.seq)) for s in SeqIO.parse(StringIO(decoded_lines), "fasta")]
 
-        return sequences
+        # Chop sequences in preparation for graph traversal
+        # TODO
+
+        # Construct sequence graph and perform random walks
+        # TODO
+
+        # Sample sequences for training
+        keep_sequences = list(filter(self.length_sampling_filter, sequences))
+
+        return keep_sequences
 
     def crop_maxlen(self, input_sequence: str, maxlen: int = None):
         # path, input_sequence = input_data