feat(evm): add witness oracle metrics - #983
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Adds the missing observability for the live pre-image witness oracle (
--witness.collect). Phase 5 (host integration) is deliberately not built — see the verdict below.What this adds
New
world_chain.witnessmetric scope (crates/evm/src/metrics.rs):captured/droppedWorldChainBlockExecutor::finishusestry_send; on a full channel it drops the witness and continues. A single drop makes every range spanning that block permanently unservable, and today that is invisible.assembly_failedinserted/evicted/cache_len/cache_oldest_block/cache_newest_blockwitness_bytes(histogram) /cache_bytes--witness.depthis a number instead of a guess.range_hit/range_miss/range_missing_blocksdebug_collectRangeWitness, and how far off a miss was.WitnessCachenow tracks retained bytes exactly across replace and eviction (new unit test covers it). All counters are inert when--witness.collectis off.Verdict on Phase 5: do not build it yet
op-rethalready ships--proofs-history, and it subsumes the witness cache for the Kona host path:rust/op-reth/crates/node/src/proof_history.rs:94-101installs RPC overrides foreth_getProofanddebug_executePayload—debug_executePayloadis the exact high-level hint the witness cache targets (kona/bin/host/src/single/handler.rs:394-421), andeth_getProofis what the current incident is about (handler.rs:296-341,:225-241).op-proofsbackfill/prune/snapshot subcommands — versus 1024 blocks (~34 min) of RAM, lost on every restart, with no backfill.build_range_inputkeeps talking standard RPC.The witness cache has one genuine advantage — zero re-execution on the serving side (op-reth still re-executes in
DebugApiExt::execute_payload,crates/rpc/src/debug.rs:194-255, it just makes the state reads fast). That advantage is real but does not justify a second, weaker mechanism before the first one is even switched on.World Chain parses
--proofs-historytoday and silently ignores it.WorldChainArgs.rollupis op-rethRollupArgs(crates/cli/src/cli.rs:8,167), which carriesproofs_history(op-reth/crates/node/src/args.rs:196), so the flags show up inspecs/cli/reference.md:79-106. World Chain only ever readssequencer,disable_txpool_gossip,discovery_v4andcompute_pending_blockfrom it — the exex and the RPC overrides are never installed. An operator who sets--proofs-historygets a node that looks configured and is not. Fixing that is the higher-priority change and it subsumes most of Phase 5.Fix concerns 2 (single-drop poisoning, no repair path) and 3 (metrics — this PR) before revisiting the witness cache at all.
🤖 Generated with Claude Code
Note
Low Risk
Observability-only changes with no altered witness serving logic; cache byte accounting is additive and covered by a new test.
Overview
Adds
world_chain.witnessPrometheus metrics for the live pre-image witness path (--witness.collect), so drops, cache bounds, memory use, and range lookup success are visible in production.WitnessMetrics(lazy singleton) records capture (captured/dropped), collector assembly failures (assembly_failed), cache lifecycle (inserted,evicted,witness_bytes,cache_bytes,cache_len, oldest/newest block gauges), andWitnessCache::rangeoutcomes (range_hit,range_miss,range_missing_blocks).WorldChainBlockExecutor::finishand the witness collector increment the failure counters; the cache updates gauges on insert and range.WitnessCachenow keeps an exact running byte total per entry (retained_bytesover state/codes/keys/headers), including on replace and eviction, with a unit test for that accounting.metrics/metrics-deriveare added toworld-chain-evm.Reviewed by Cursor Bugbot for commit 55005fe. Configure here.