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Validate llama.cpp slot prompt-cache persistence as a save-and-restore lifecycle for a specific state.
Validate llama.cpp slot prompt-cache persistence as a save-and-restore lifecycle for a specific state. Successfully writing a file does not establish that another build, model, or context configuration can restore it. Pin those dependencies and test positive and negative cases. This differs from an ordinary prefix-cache hit: it moves state across explicit server-slot lifecycle boundaries rather than merely reusing memory already present in a running process.
Define the state boundary
The server README documents slot-save-path and save, restore, and erase actions. Identify the slot and expected post-restore behavior first. Do not treat its file as a model-independent conversation archive. Text history and internal computational state are different artifacts. Preserve the original prompt separately so that ordinary prefill can reconstruct the required work when restoring binary state is unsuitable. This makes the fallback explicit rather than depending on undocumented portability across arbitrary checkpoints or builds.
Exercise a reproducible lifecycle
On an isolated instance, run a fixed prompt, wait for completion, save the slot, and record build, model revision, and context settings. Perform the lifecycle transition specified by the test and restore the file. Avoid changing quantization and cache settings simultaneously. Retain the filename and actual action result. HTTP success and nonzero file size are useful observations, but acceptance ends only after restored state and the intended continuation have been checked. They cannot be inferred from a successful save response alone.
Include negative fixtures
Test an unsuitable file and state exceeding the chosen slot context. The server implementation validates restored tokens, size, and associated state completeness. These branches should produce understandable rejection rather than silently consume invalid state. This is an acceptance design, not advice to damage a production cache file. Use separate fixtures and preserve a valid original. If the runtime falls back to prompt reprocessing, distinguish it from successful restoration so that recomputed work is not wrongly credited to the saved artifact.
Account for associated state
Depending on the execution mode, state can include related checkpoints or speculative-draft components. Do not generalize a simple text test to every speculative or multimodal path. Read the selected release’s conditions and retain diagnostics. Associate files with the correct slot and test workflow so that another fixture is not restored through an accidentally reused name. A manifest should identify model and build; a filename alone cannot establish the content’s compatibility or intended ownership within an operational test.
Document recovery choices
State where restoration is permitted and where the original prompt must be recomputed. Incompatibility does not justify promising universal binary-state migration. Preserve functional results and separate file reading from subsequent warmup when timing the path. Revalidate after llama.cpp upgrades before opening ordinary traffic. The package contains source input, state file, manifest, and acceptance log. It should distinguish restoration from recomputation without presenting every successfully saved prompt cache as a durable portable format across versions, devices, and arbitrary models.
Related reading
Prefix caching: when repeated context helps a GPU pool; Reproducible inference stacks: preserving a GPU pilot’s result.