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perf(lite-backend): share unchanged witness states between blocks

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Each scanned block deep-copied the newest witness of every note with
history to start that block's entry, although a block without shielded
outputs changes no witness, and spent or pending notes never change
theirs. A note's 100-entry list was 100 separate copies, mostly
identical.

The list now holds Arc-shared witnesses. The per-block duplicate is an
Arc::clone, and Arc::make_mut copies the newest entry only for unspent,
non-pending notes and only in blocks with at least one shielded output.
Every entry is still written in full, so the file is unchanged, and a
spend takes its own copy of the witness. A loaded wallet is not
de-duplicated, so the saving builds up over the next 100 blocks.

No output change: the saved bytes are identical; notes use less memory.
With 1000 live notes x 100 witnesses (a 70 MB file), RssAnon after 100
blocks without outputs is 18 MiB instead of 189 MiB and such a block
scans in 1.0 ms instead of 2.1-2.7 ms; when every block has an output,
the live bytes stay about the same.

The witness tests, the 1000-seed oracle and a differential run against
the unmodified backend (every witness entry and the whole saved file
after every operation; only the cleared lists and the chosen spend notes
may differ) all pass, and the measured wallet saves to the same SHA-256
as with the old build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
DanS
2026-10-10 09:50:03 -05:00
co-authored by Claude Opus 5.5
parent 6f1ae874fb
commit ba08cab95a
2 changed files with 21 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
third_party/silentdragonxlite/silentdragonxlite-cli/lib/src/lightwallet.rs
Vendored
+15 -9
View File
@@ -2304,10 +2304,10 @@ pub fn scan_full_mempool_tx(&self, tx: &Transaction, height: i32, _datetime: u64
// Prepare the note witnesses for updating
for tx in txs.values_mut() {
for nd in tx.notes.iter_mut() {
// Duplicate the most recent witness (nothing to do for notes with no history)
// Duplicate the most recent witness (shares the allocation; deep-cloned only when appended to)
if let Some(witness) = nd.witnesses.last() {
let clone = witness.clone();
nd.witnesses.push(clone);
let shared = Arc::clone(witness);
nd.witnesses.push(shared);
// Trim the oldest witnesses in place (no fresh Vec per note per block)
let len = nd.witnesses.len();
if len > MAX_REORG {
@@ -2322,12 +2322,18 @@ pub fn scan_full_mempool_tx(&self, tx: &Transaction, height: i32, _datetime: u64
let extfvks: Vec<ExtendedFullViewingKey> = self.zkeys.read().unwrap().iter().map(|zk| zk.extfvk.clone()).collect();
// Create a single mutable slice of all the newly-added witnesses.
let mut witness_refs: Vec<_> = txs
.values_mut()
.map(|tx| tx.notes.iter_mut().filter_map(
|nd| if nd.spent.is_none() && nd.unconfirmed_spent.is_none() { nd.witnesses.last_mut() } else { None }))
.flatten()
.collect();
// A block without shielded outputs appends nothing to any witness: don't un-share (deep-clone) them.
let block_has_outputs = block.vtx.iter().any(|t| !t.outputs.is_empty());
let mut witness_refs: Vec<&mut IncrementalWitness<Node>> = if block_has_outputs {
txs
.values_mut()
.map(|tx| tx.notes.iter_mut().filter_map(
|nd| if nd.spent.is_none() && nd.unconfirmed_spent.is_none() { nd.witnesses.last_mut().map(|w| Arc::make_mut(w)) } else { None }))
.flatten()
.collect()
} else {
Vec::new()
};
self.scan_block_internal(
block.clone(),