sgl-project/sglang · error · ValueError

DSpark requires --speculative-dspark-block-size to be positi

Error message

DSpark requires --speculative-dspark-block-size to be positive, got {}.

What it means

The DSpark block size (gamma, the number of draft tokens per step) must be a positive integer. Non-positive values break the gamma+1 verify-window arithmetic and are rejected up front.

Source

Thrown at python/sglang/srt/arg_groups/speculative_hook.py:473

    from sglang.srt.speculative.dspark_components.dspark_config import (
        DEFAULT_DSPARK_GAMMA,
        read_draft_checkpoint_config,
    )

    draft_config = None
    try:
        draft_config = read_draft_checkpoint_config(server_args=server_args)
    except Exception as e:
        logger.warning(
            "Failed to read DSpark draft config; preserving explicit/default "
            "gamma resolution. Error: %s",
            e,
        )

    gamma: Optional[int] = None
    if cfg.speculative_dspark_block_size is not None:
        if int(cfg.speculative_dspark_block_size) <= 0:
            raise ValueError(
                "DSpark requires --speculative-dspark-block-size to be positive, "
                f"got {cfg.speculative_dspark_block_size}."
            )
        gamma = int(cfg.speculative_dspark_block_size)
    else:
        if draft_config is not None:
            gamma = draft_config.resolve_gamma(default=None)
        if gamma is None and cfg.speculative_num_draft_tokens is None:
            gamma = DEFAULT_DSPARK_GAMMA
            logger.warning(
                "DSpark gamma is not set; defaulting to %d.",
                gamma,
            )

    if gamma is not None:
        verify_window = int(gamma) + 1
        if (
            cfg.speculative_num_draft_tokens is not None

View on GitHub (pinned to 0132848349)

Solutions

1. Set --speculative-dspark-block-size to a positive int (typical gamma 3-8)
2. Omit the flag to let DSpark infer gamma from the draft config
3. Sanity-check the value in your launch script before passing it

Example fix

# before
--speculative-dspark-block-size 0
# after
--speculative-dspark-block-size 4

if args.speculative_dspark_block_size is not None and int(args.speculative_dspark_block_size) <= 0:
    raise SystemExit('dspark block size (gamma) must be positive')

When it happens

Trigger: Passing --speculative-dspark-block-size 0 or negative on a DSpark launch.

Common situations: Placeholder 0 in templated configs meaning 'auto'; env interpolation errors; copy from a different algorithm's flag semantics.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• DFLASH requires --speculative-dflash-block-size to be positi
• DSpark speculative_num_draft_tokens must be >= 2 (= gamma +
• DSPARK requires explicit layer_ids for aux hidden capture.
• Unknown match_type: '{match_type}'. Must be 'BFS' or 'PROB'.
• Kimi-K3 DCP + DSPARK currently requires SGLANG_RAGGED_VERIFY

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/6bb5022b1008cc19. Report an issue: GitHub.