sgl-project/sglang · error · NotImplementedError

protected_size() is not implemented; use full_protected_size

Error message

protected_size() is not implemented; use full_protected_size() and swa_protected_size() instead

What it means

Symmetric to evictable_size: SWARadixCache splits protected sizes into full and SWA domains, so protected_size() raises NotImplementedError by design. Use full_protected_size() and swa_protected_size().

Source

Thrown at python/sglang/srt/mem_cache/swa_radix_cache.py:865

            node = node.parent

    def sanity_check(self):
        self.full_lru_list.sanity_check(self)
        self.swa_lru_list.sanity_check(self)

    def evictable_size(self) -> Tuple[int, int]:
        # Note: use full_evictable_size() and swa_evictable_size() instead.
        raise NotImplementedError

    def full_evictable_size(self) -> int:
        return self.full_evictable_size_

    def swa_evictable_size(self) -> int:
        return self.swa_evictable_size_

    def protected_size(self) -> Tuple[int, int]:
        # Note: use full_protected_size() and swa_protected_size() instead.
        raise NotImplementedError

    def full_protected_size(self) -> int:
        # protected size refers to the size of the full cache that is locked
        return self.full_protected_size_

    def swa_protected_size(self) -> int:
        # protected size refers to the size of the swa cache that is locked
        return self.swa_protected_size_

    def all_values_flatten(self) -> torch.Tensor:
        values = []

        def _dfs_helper(node: TreeNode):
            for _, child in node.children.items():
                values.append(child.value)
                _dfs_helper(child)

        _dfs_helper(self.root_node)

View on GitHub (pinned to 0132848349)

Solutions

1. Use full_protected_size() and swa_protected_size()
2. Guard with hasattr/try when supporting both SWA and non-SWA caches

Example fix

# before
prot = tree.protected_size()
# after
prot_full = tree.full_protected_size()
prot_swa = tree.swa_protected_size()

if hasattr(tree, 'swa_protected_size'):
    prot = (tree.full_protected_size(), tree.swa_protected_size())

def has_split_protected_sizes(tree) -> bool:
    return hasattr(tree, 'full_protected_size') and hasattr(tree, 'swa_protected_size')

When it happens

Trigger: Calling protected_size() on SWARadixCache from generic cache accounting code.

Common situations: Scheduler/metrics code ported from the non-SWA RadixCache path that queries protected_size.

Related errors

• evictable_size() is not implemented; use full_evictable_size
• {self.__class__.__name__}.apply should not be called.
• Use get_key_buffer instead.
• Host cache is not supported yet
• SWA Radix tree sanity check failed, ping @hanming-lu: {e}

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/d041f811511a0057. Report an issue: GitHub.