scripts/prune_checkpoints.py

"""Strip `train_state/` from all but the newest checkpoint, so a long run fits on disk.

    uv run python scripts/prune_checkpoints.py CKPT_ROOT              # one shot
    uv run python scripts/prune_checkpoints.py CKPT_ROOT --watch      # every 5 min, until Ctrl+C
    uv run python scripts/prune_checkpoints.py CKPT_ROOT --dry-run

Each openpi checkpoint holds:
    params/       12.5 GiB   the weights -- this is what you ship and serve
    train_state/  37.5 GiB   params + Adam mu + nu -- only needed to RESUME
    assets/       tiny       norm_stats.json, needed at serve time

With `save_interval=2500` and `keep_period=2500` every save lands on a keep_period multiple, so
orbax retains all 12 permanently: 12 x 50 GiB = 600 GiB. Keeping `train_state/` only for the
newest checkpoint brings that to 12 x 12.5 + 37.5 = 188 GiB, and costs nothing except that you
can only resume from the most recent checkpoint.

Safety: never touches the newest step, skips in-progress writes (`*.orbax-checkpoint-tmp-*` and
any step lacking `_CHECKPOINT_METADATA`), and only ever removes directories named `train_state`.
"""
import argparse
import pathlib
import shutil
import sys
import time


def log(*a):
    print(*a, flush=True)


def du(p: pathlib.Path) -> int:
    return sum(f.stat().st_size for f in p.rglob("*") if f.is_file())


def sweep(root: pathlib.Path, dry: bool, min_step: int = 0) -> tuple[int, int]:
    steps = []
    for d in root.iterdir():
        if not d.is_dir() or not d.name.isdigit():
            continue
        if not (d / "_CHECKPOINT_METADATA").exists():
            log(f"  skip {d.name}: still being written (no _CHECKPOINT_METADATA)")
            continue
        steps.append(int(d.name))
    if not steps:
        return 0, 0
    newest = max(steps)
    freed, n = 0, 0

    # Whole-checkpoint deletion below min_step. openpi's keep_period is uniform, so the only
    # way not to spend 12.5 GiB on a checkpoint too early to be useful is to remove it after
    # the fact. Never touches the newest, so resume always works.
    for s in sorted(steps):
        if min_step and s < min_step and s != newest:
            d = root / str(s)
            size = du(d)
            log(f"  {'would delete' if dry else 'deleting'} {s}/ entirely  {size/2**30:.1f} GiB"
                  f"  (below --min-step {min_step})")
            if not dry:
                shutil.rmtree(d)
            freed += size
            n += 1
    steps = [s for s in steps if not (min_step and s < min_step and s != newest)]

    for s in sorted(steps):
        ts = root / str(s) / "train_state"
        if s == newest:
            if ts.exists():
                log(f"  keep {s}: newest, train_state retained for resume")
            continue
        if not ts.exists():
            continue
        size = du(ts)
        log(f"  {'would remove' if dry else 'removing'} {s}/train_state  {size/2**30:.1f} GiB")
        if not dry:
            shutil.rmtree(ts)
        freed += size
        n += 1
    return freed, n


def main() -> int:
    ap = argparse.ArgumentParser()
    ap.add_argument("root", help="e.g. ~/openpi/checkpoints/pi05_g1_pickplace/pickplace_full_v1")
    ap.add_argument("--watch", action="store_true", help="keep sweeping every --interval seconds")
    ap.add_argument("--interval", type=int, default=300)
    ap.add_argument("--min-step", type=int, default=0,
                    help="delete checkpoints below this step entirely (params included). Use to "
                         "avoid spending 12.5 GiB each on checkpoints too early to be useful.")
    ap.add_argument("--dry-run", action="store_true")
    a = ap.parse_args()

    root = pathlib.Path(a.root).expanduser()
    if not root.is_dir():
        if not a.watch:
            log(f"not a directory: {root}")
            return 1
        # In --watch mode the training run may not have created it yet. Wait rather than exit,
        # so this can be launched immediately after training without a race.
        log(f"waiting for {root} to appear...")
        while not root.is_dir():
            time.sleep(5)
        log(f"{root} exists, starting to watch")

    while True:
        total, freed_now = du(root), 0
        log(f"[{time.strftime('%H:%M:%S')}] {root.name}: {total/2**30:.1f} GiB on disk")
        freed, n = sweep(root, a.dry_run, a.min_step)
        if n:
            log(f"  {'would free' if a.dry_run else 'freed'} {freed/2**30:.1f} GiB "
                  f"from {n} checkpoint(s)")
        if not a.watch:
            return 0
        time.sleep(a.interval)


if __name__ == "__main__":
    sys.exit(main())