comfy-custom-nodes-caching

Execution caching fallback

A node declares its cache signature with fingerprint_inputs (V3) or IS_CHANGED (V1). Declaring neither lets the node's declared inputs decide, which is the right default; add one only when the output depends on something those inputs do not capture.

The signature is taken before the graph runs, so a linked input arrives as None — only widget values, literals and the UNIQUE_ID hidden are real. The other hiddens are not: the signature pass calls get_input_data with no dynamic prompt and no extra data, so PROMPT arrives as {} and DYNPROMPT, EXTRA_PNGINFO, EXECUTION_LIST and the auth-token hiddens arrive as None. Fingerprinting one of those yields a constant, which is the stale-output failure this file warns about. The exception is an input declaring rawLink, handed its [node_id, output_index] reference instead. Reaching into a tensor or model through either form raises, and the executor catches that, logs a warning, and makes the signature a not-a-number value that never compares equal to itself. A broken signature therefore shows up as a node that recomputes every run — never as a crash. Return scalars, and lists/tuples/dicts whose keys are all one type, of scalars: a set, a non-str Enum or a dataclass becomes an unhashable sentinel that recomputes every run, and a dict with mixed-type keys raises outside that handler.

The signature is not local: a node's cache key embeds every ancestor's signature, so one value that never repeats forces its whole downstream cone to recompute. A wall-clock reading is the usual cause — correct for a live fetch that must always re-read, a cache defeat for everything after it. Derive the value from what the output depends on: resolved widget values, plus external state the node reads, such as a file's size and modification time — a content digest instead, as core's LoadImage does, when a file may be rewritten in place and leave both unchanged — environment variables, and a version constant bumped when behaviour changes.

Prove both halves: call the signature twice with identical arguments and require equality, then change one field and require a difference. Failing the first is a cache defeat; failing the second is a stale-output bug. Marking a node non-idempotent or as producing intermediate output changes cache behaviour separately and does not substitute for a correct signature.