Problem
CDBIterator::GetKey() only deserializes the current LevelDB key once and GetKeyImpl() already exposes that key as a contiguous borrowed byte span, and GetKey() creates a fresh local reader and only performs immediate forward reads before returning.
The copied DataStream currently insulates the iterator entry from a failed decode, so switching to a borrowed reader is only safe if a deserialization failure still returns false and leaves the same key/value readable afterward.
[!NOTE] The same simplification does not apply to
GetValue(), because that path deobfuscates the value bytes in place first and still needs an owning mutable buffer.
Fix
Add a preparatory test with an invalid reads and checks that the failed decode does not consume the current iterator entry.
Then switch GetKey() to SpanReader so the key bytes are read in place instead of being copied into a temporary DataStream.
This keeps the same exception swallowing and bool return semantics while avoiding the extra allocation and copy.
Context
Reproducer
gettxoutsetinfo is ~10-12% faster for up-to-date blocks (run on SSD), see:
<details><summary>2026-04-20 | gettxoutsetinfo | rpi5-8 | aarch64 | Cortex-A76 | 4 cores | 7.7Gi RAM | ext4 | SSD</summary>
COMMITS="64a88c8c1edc7ee5cef623d9aa8179a239e27ce9 57dc0202ddb7b4cbdd521fb237a25fc4d7f28ddf"; \
BASE_DIR="/mnt/my_storage"; DATA_DIR="$BASE_DIR/BitcoinData"; LOG_DIR="$BASE_DIR/logs"; \
mkdir -p "$LOG_DIR" && \
(echo ""; for c in $COMMITS; do git cat-file -e "$c^{commit}" 2>/dev/null || git fetch -q origin "$c" || exit 1; git log -1 --pretty='%h %s' "$c" || exit 1; done) && \
(echo "" && echo "$(date -I) | gettxoutsetinfo | $(hostname) | $(uname -m) | $(lscpu | grep 'Model name' | head -1 | cut -d: -f2 | xargs) | $(nproc) cores | $(free -h | awk '/^Mem:/{print $2}') RAM | $(df -T $BASE_DIR | awk 'NR==2{print $2}') | $(lsblk -no ROTA $(df --output=source $BASE_DIR | tail -1) | grep -q 1 && echo HDD || echo SSD)"; echo "") && \
hyperfine \
--sort command \
--runs 10 \
--export-json "$BASE_DIR/gettxoutsetinfo-$(sed -E 's/([a-f0-9]{8})[a-f0-9]* ?/\1-/g;s/-$//'<<<"$COMMITS")-$(date +%s).json" \
--parameter-list COMMIT ${COMMITS// /,} \
--prepare "killall -9 bitcoind 2>/dev/null || true; rm -f $DATA_DIR/debug.log; git clean -fxd && git reset --hard {COMMIT} && \
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release && ninja -C build bitcoind bitcoin-cli -j$(nproc) && \
./build/bin/bitcoind -datadir=$DATA_DIR -connect=0 -listen=0 -dnsseed=0 -coinstatsindex=0 -txindex=0 -blockfilterindex=0 -daemon -printtoconsole=0; \
./build/bin/bitcoin-cli -datadir=$DATA_DIR -rpcwait getblockcount >/dev/null" \
--conclude "./build/bin/bitcoin-cli -datadir=$DATA_DIR stop 2>/dev/null || true; killall bitcoind 2>/dev/null || true; sleep 10; \
grep -q 'Done loading' $DATA_DIR/debug.log && grep 'Bitcoin Core version' $DATA_DIR/debug.log | grep -q \"\$(git rev-parse --short=12 {COMMIT})\"; \
cp $DATA_DIR/debug.log $LOG_DIR/gettxoutsetinfo-{COMMIT}-$(date +%s).log" \
"./build/bin/bitcoin-cli -datadir=$DATA_DIR -rpcclienttimeout=0 -named gettxoutsetinfo hash_type='none' use_index='false' >/dev/null"
64a88c8c1e Merge bitcoin/bitcoin#35096: kernel: align height parameters to int32_t in btck API
57dc0202dd dbwrapper: use SpanReader for iterator keys
Benchmark 1: ./build/bin/bitcoin-cli -datadir=/mnt/my_storage/BitcoinData -rpcclienttimeout=0 -named gettxoutsetinfo hash_type='none' use_index='false' >/dev/null (COMMIT = 64a88c8c1edc7ee5cef623d9aa8179a239e27ce9)
Time (mean ± σ): 109.002 s ± 3.091 s [User: 0.003 s, System: 0.004 s]
Range (min … max): 106.191 s … 113.608 s 10 runs
Benchmark 2: ./build/bin/bitcoin-cli -datadir=/mnt/my_storage/BitcoinData -rpcclienttimeout=0 -named gettxoutsetinfo hash_type='none' use_index='false' >/dev/null (COMMIT = 57dc0202ddb7b4cbdd521fb237a25fc4d7f28ddf)
Time (mean ± σ): 97.711 s ± 1.172 s [User: 0.003 s, System: 0.004 s]
Range (min … max): 96.651 s … 100.104 s 10 runs
Relative speed comparison
1.12 ± 0.03 ./build/bin/bitcoin-cli -datadir=/mnt/my_storage/BitcoinData -rpcclienttimeout=0 -named gettxoutsetinfo hash_type='none' use_index='false' >/dev/null (COMMIT = 64a88c8c1edc7ee5cef623d9aa8179a239e27ce9)
1.00 ./build/bin/bitcoin-cli -datadir=/mnt/my_storage/BitcoinData -rpcclienttimeout=0 -named gettxoutsetinfo hash_type='none' use_index='false' >/dev/null (COMMIT = 57dc0202ddb7b4cbdd521fb237a25fc4d7f28ddf)
</details>
