The custom episode pool becomes a pure `datasets` pipeline:
split_dataset_by_node -> batch(by_column="episode_index")
-> shuffle(buffer=episode_pool_size) # episode pool
-> map(explode + exact delta windows) # episode -> frames
-> shuffle(buffer=frame_shuffle_buffer_size) # frame interleave
and the torch IterableDataset wrapper keeps only per-sample video decode
(decode-on-exit), image transforms, task lookup, and decode/fetch timing.
Replaced by native machinery and deleted: the pooled-episode admission
loop, the refcounted video prefetcher, manual worker shard striding plus
the worker-split suppression patch, the per-(epoch, rank) shard-order
permutation, the per-consumer SplitMix64 RNG, and fast-forward resume.
DataLoader workers are split by `datasets` itself; .shuffle() permutes
shard order per epoch natively; resume delegates to the native
state_dict/load_state_dict (exact with num_workers=0; with workers use
torchdata's StatefulDataLoader, which checkpoints per-worker state
through the same protocol). An in-flight epoch counter ensures a
mid-iteration state_dict records the epoch the stream position belongs
to. Buffer contents are skipped on resume (documented datasets
behavior): never repeats data, drops at most ~pool + frame-buffer frames.
Randomness is unchanged: a batch still mixes up to episode_pool_size
episodes; delta windows are still exact in-episode slices with correct
boundary padding (value-verified against the map-style dataset). The
known trade accepted with this rewrite: no video prefetch-on-admit, so
remote decode pays per-frame range reads at yield time - use a colocated
bucket (data_files_root) at large scale.
The delta-consistency tests gained a scalar-comparison branch: they
silently skipped python-scalar keys before (stale `check` variable),
exposed by the new pipeline's key ordering.
Requires datasets with #8259 (pinned to the merge commit on this
branch). Example updated to per-rank native resume via torchdata's
StatefulDataLoader when available.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Replace the shard/Backtrackable/decoded-shuffle-buffer internals with an
episode pool: each (rank x worker) consumer keeps episode_pool_size whole
episodes' tabular rows in RAM and emits uniformly random frames across
them. delta_timestamps windows become exact in-RAM slices with correct
boundary padding (the Backtrackable machinery and its lookback/lookahead
ceilings are gone), and video is decoded only when a sample is emitted,
so pool memory stays tabular-sized instead of buffer_size decoded
samples.
- Prefetch-on-admit: when streaming from a remote source, each pooled
episode's video files download to a local cache in the background
(refcounted, since v3 packs several episodes per file; deleted on
eviction), so decode-on-exit reads local bytes instead of paying
network seek latency.
- Per-consumer RNG derived from (seed, epoch, rank, worker): consumers
decorrelated, runs reproducible, epochs reshuffle automatically.
- Deterministic fast-forward resume: load_state_dict takes the trainer's
{batches_consumed, batch_size}; each worker re-derives its own skip
from the DataLoader's round-robin batch assignment and replays
tabular-only (no decode). Exact within an epoch, works with
num_workers > 0, and the same state file serves every rank. Replaces
the per-shard HF state_dict approach, which lived in worker processes
and could not be captured from the trainer.
- Shard-cap default removed (max_num_shards=None uses every parquet
shard); runtime warnings for non-divisible world sizes (datasets
degrades to read-everything splitting) and workers left without
shards.
- episode_pool_size replaces buffer_size (deprecated, ignored with a
warning); decoder cache sized to the pool working set, capped at 128.
Legacy order-replication tests asserted the old buffer algorithm
step-by-step and are rewritten as behavior contracts (exactly-once
coverage, per-seed determinism, epoch reshuffle). Value-level parity
tests against the map-style dataset pass unchanged.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* chore: replace hard-coded 'action' values with constants throughout all the source code
* chore(tests): replace hard-coded action values with constants throughout all the test code
Pepijn