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Add debug logging for remote iterator #3916

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Add debug logging for remote iterator #3916

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27 changes: 27 additions & 0 deletions src/maxtext/input_pipeline/multihost_dataloading.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
Adapted from Sholto's:
https://github.com/sholtodouglas/multihost_dataloading
"""
import logging
from functools import partial
from typing import Union, Sequence
from collections.abc import Iterator, Iterable
Expand Down Expand Up @@ -198,6 +199,11 @@ def reset(self):
def get_next(self, dummy_array):
"""Gets the next batch of data and forms a global array."""
local_data = next(self.iterator)
logging.info(
"RemoteIterator get_next got local_data['inputs'] of shape %s, will split into %s devices",
local_data["inputs"].shape,
len(list(dummy_array.sharding.addressable_devices)),
)
Comment on lines +202 to +206
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@bvandermoon bvandermoon May 18, 2026

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Why not max_logging?


def form_global_array_colocated_python(path, array, devices, global_shape, sharding):
try:
Expand All @@ -223,6 +229,13 @@ def form_global_array_colocated_python(path, array, devices, global_shape, shard

def save_state(self, step_array):
"""Saves the iterator state to a file."""
logging.info(
"RemoteIterator save_state received step_array shape %s, num addressable shards %s, shard 0 shape %s",
str(step_array.shape),
str(len(step_array.addressable_shards)),
str(step_array.addressable_data(0).shape),
)
logging.info("RemoteIterator step_array.addressable_data(0) is %s", str(step_array.addressable_data(0)))
step = step_array.addressable_data(0).item()
directory = epath.Path(self.checkpoint_path) / str(step) / "iter"
if self.elastic:
Expand All @@ -242,6 +255,14 @@ def save_state(self, step_array):
return step_array

def restore_state(self, step_array):
"""Restore the iterator state from a checkpoint."""
logging.info(
"RemoteIterator restore_state received step_array shape %s, num addressable shards %s, shard 0 shape %s",
str(step_array.shape),
str(len(step_array.addressable_shards)),
str(step_array.addressable_data(0).shape),
)
logging.info("RemoteIterator step_array.addressable_data(0) is %s", str(step_array.addressable_data(0)))
step = step_array.addressable_data(0).item()
directory = epath.Path(self.checkpoint_path) / str(step) / "iter"
if self.elastic:
Expand All @@ -257,12 +278,16 @@ class RemoteIteratorWrapper:
"""Wrapper for RemoteIterator that handles device placement."""

def __init__(self, get_ds_fn, preprocessing_fn, global_mesh, global_shape, checkpoint_path="", elastic=False):
max_logging.log(f"RemoteIteratorWrapper: received global_mesh = {global_mesh}")
max_logging.log(f"RemoteIteratorWrapper: received global_shape = {global_shape}")
self.cpu_devices = _colocated_cpu_devices(jax.local_devices())
self.tpu_devices = jax.local_devices()
self.cpu_mesh = _colocated_cpu_mesh(global_mesh)
self.tpu_sharding = jax.sharding.NamedSharding(global_mesh, PartitionSpec(global_mesh.axis_names))
self.cpu_sharding = jax.sharding.NamedSharding(self.cpu_mesh, PartitionSpec(self.cpu_mesh.axis_names))
self.dummy_array = jnp.zeros((len(self.cpu_devices)))
max_logging.log(f"RemoteIteratorWrapper: number of cpu devices {len(self.cpu_devices)}")
max_logging.log(f"RemoteIteratorWrapper: cpu_sharding: {self.cpu_sharding}")
self.dummy_array = jax.device_put(self.dummy_array, self.cpu_sharding)
# This is a proxy to a RemoteIterator running in a colocated process,
# named "local_iterator" to match MultiHostDataLoadIterator's interface.
Expand All @@ -282,10 +307,12 @@ def __next__(self):

def save_state(self, step):
step_array = jnp.full(self.dummy_array.shape, step, dtype=jnp.int32)
max_logging.log(f"RemoteIteratorWrapper: calling saving_state with {step_array.shape=}")
step_array = jax.device_put(step_array, self.cpu_sharding)
self.local_iterator.save_state(step_array)

def restore_state(self, step):
step_array = jnp.full(self.dummy_array.shape, step, dtype=jnp.int32)
max_logging.log(f"RemoteIteratorWrapper: calling restore_state with {step_array.shape=}")
step_array = jax.device_put(step_array, self.cpu_sharding)
self.local_iterator.restore_state(step_array)
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