From de829684400c68a4a40bc2f91de04add2f6a9f10 Mon Sep 17 00:00:00 2001
From: Abhishek Enaguthi <enaguthiabhishek@gmail.com>
Date: Wed, 8 Jul 2026 18:41:26 -0700
Subject: [PATCH] fix: retry transient parquet read failures in training

ParquetDataset read errors (e.g. transient HTTP/IO while reading
hub-cached parquet) crash long training runs. Retry with exponential
backoff; configurable via data.dataset_read_retries (default 3).

Fixes #100
---
 src/zeroband/config.py |  1 +
 src/zeroband/data.py   | 33 +++++++++++++++++++++++++++++----
 tests/test_data.py     | 30 ++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/src/zeroband/config.py b/src/zeroband/config.py
index 11c27af5..9f7b7a0a 100644
--- a/src/zeroband/config.py
+++ b/src/zeroband/config.py
@@ -26,6 +26,7 @@ class DataConfig(BaseConfig):
     data_world_size: int | None = None
     reverse_data_files: bool = False
     split_by_data_rank: bool = True
+    dataset_read_retries: int = 3
 
 
 class AdamConfig(BaseConfig):
diff --git a/src/zeroband/data.py b/src/zeroband/data.py
index 50ff1f58..f42751b7 100644
--- a/src/zeroband/data.py
+++ b/src/zeroband/data.py
@@ -1,5 +1,6 @@
 from dataclasses import dataclass, asdict
 import random
+import time
 from typing import Any, Generator, Optional, List, Dict, TypedDict, Union
 import functools
 import threading
@@ -149,12 +150,31 @@ class ParquetDataset(IterableDataset, Stateful):
     * [ ] handle mutli proc dataloader pytorch
     """
 
-    def __init__(self, files: List[str], tokenizer: PreTrainedTokenizer):
+    def __init__(self, files: List[str], tokenizer: PreTrainedTokenizer, read_retries: int = 3):
         self.arg_files = files
         self.tokenizer = tokenizer
+        self.read_retries = read_retries
 
         self.state = None
 
+    def _read_text_column(self, file: str):
+        last_error: Exception | None = None
+        for attempt in range(self.read_retries):
+            try:
+                parquet_file = pq.ParquetFile(file)
+                return parquet_file.read()["text"]
+            except Exception as e:
+                last_error = e
+                if attempt + 1 >= self.read_retries:
+                    break
+                delay = min(2**attempt, 30)
+                get_logger().warning(
+                    f"Failed to read parquet {file!r} ({e}); retry {attempt + 1}/{self.read_retries} in {delay}s"
+                )
+                time.sleep(delay)
+        assert last_error is not None
+        raise last_error
+
     def _lazy_init(self):
         worker_info = torch.utils.data.get_worker_info()
         if worker_info is not None:
@@ -185,8 +205,7 @@ def __iter__(self):
         while True:
             file = self.state.files[self.state.file_index]
 
-            parquet_file = pq.ParquetFile(file)
-            table = parquet_file.read()["text"]
+            table = self._read_text_column(file)
 
             while True:
                 row = table[self.state.row_index]
@@ -452,6 +471,7 @@ def _load_datasets(
     streaming: bool = True,
     probabilities: Optional[List[float]] = None,
     reverse_data_files: bool = False,
+    dataset_read_retries: int = 3,
 ) -> InterleaveDataset:
     get_logger().debug(dataset_names)
     ds_args = []
@@ -475,7 +495,11 @@ def _load_datasets(
     datasets = []
     for ds_arg in ds_args:
         # logger.debug(f"Loading dataset: {ds_arg['data_files']}")
-        _ds = ParquetDataset(files=ds_arg["data_files"], tokenizer=tokenizer)
+        _ds = ParquetDataset(
+            files=ds_arg["data_files"],
+            tokenizer=tokenizer,
+            read_retries=dataset_read_retries,
+        )
         datasets.append(_ds)
 
     if len(datasets) > 1:
@@ -526,6 +550,7 @@ def load_all_datasets(
         probabilities=_get_probabilities(data_config),
         reverse_data_files=data_config.reverse_data_files,
         tokenizer=tokenizer,
+        dataset_read_retries=data_config.dataset_read_retries,
     )
 
     get_logger().info(f"Train dataset: {ds}")
diff --git a/tests/test_data.py b/tests/test_data.py
index fff9d537..82bbcd37 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -1,5 +1,6 @@
 import copy
 import torch
+from unittest.mock import patch
 from zeroband.data import InterleaveDataset, ParquetDataset, SequencePackingDataSet, collate_fn
 from torch.utils.data import DataLoader
 from zeroband.data import load_all_datasets, DataConfig
@@ -270,3 +271,32 @@ def test_dataloader_parquet_dataset(parquet_files, tokenizer, num_workers):
             assert (batch1["input_ids"] == batch2["input_ids"]).all()
             assert (batch1["labels"] == batch2["labels"]).all()
             assert (batch1["seqlens"] == batch2["seqlens"]).all()
+
+
+def test_parquet_dataset_retries_transient_read_failure(parquet_files, tokenizer):
+    dataset = ParquetDataset(parquet_files[:1], tokenizer, read_retries=3)
+    real_parquet_file = pq.ParquetFile
+    attempts = 0
+
+    def flaky_parquet_file(path):
+        nonlocal attempts
+        attempts += 1
+        if attempts == 1:
+            raise OSError("HTTP 443 connection reset")
+        return real_parquet_file(path)
+
+    with patch("zeroband.data.pq.ParquetFile", side_effect=flaky_parquet_file):
+        with patch("zeroband.data.time.sleep"):
+            table = dataset._read_text_column(parquet_files[0])
+
+    assert len(table) == 100
+    assert attempts == 2
+
+
+def test_parquet_dataset_read_failure_after_retries(parquet_files, tokenizer):
+    dataset = ParquetDataset(parquet_files[:1], tokenizer, read_retries=2)
+
+    with patch("zeroband.data.pq.ParquetFile", side_effect=OSError("HTTP 443")):
+        with patch("zeroband.data.time.sleep"):
+            with pytest.raises(OSError, match="HTTP 443"):
+                dataset._read_text_column(parquet_files[0])