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//! `Shard::fold` — the seq-ordered result reducer — plus its small
//! free-fn helpers. Same `impl<C: Commands> Shard<C>` as [`crate::exec`];
//! split out so that file stays under the 500-LOC house rule.
use crate::Commands;
use crate::message::{Agg, Part, PendingSlot, SmallReply};
use crate::reduce::{drain_front, materialize};
use crate::shard::Shard;
use kevy_resp::ArgvView;
impl<C: Commands> Shard<C> {
/// Fold a sub-result into its slot; emit completed replies in seq order.
/// The `WatchCollect` / `ExecPrep` accumulators don't materialise to RESP
/// bytes — they hand off to [`crate::exec_watch`] for the conn-state
/// mutation + downstream dispatch they require.
// LOC-WAIVER: data-driven aggregation match table — one arm per
// (Agg, Part) pairing + the finalize dispatch over orchestrator aggs.
pub(crate) fn fold(&mut self, conn_id: u64, seq: u64, part: Part) {
let watch_agg: Option<Agg> = {
let Some(conn) = self.conns.get_mut(&conn_id) else {
return;
};
if seq < conn.next_emit {
return; // already emitted (defensive — shouldn't happen)
}
let idx = (seq - conn.next_emit) as usize;
let Some(slot) = conn.pending.get_mut(idx) else {
return;
};
// (Agg::AllOk, Part::Ok) `{}` body matches the catch-all `_ => {}`
// body but documents the *expected* aggregator/part pairing — the
// wildcard arm is the fallback for impossible combinations after
// the dispatcher arms. match_same_arms would collapse the two and
// hide the contract; keep them separate.
#[allow(clippy::match_same_arms)]
match (&mut slot.agg, part) {
(Agg::First(dst), Part::Reply(b)) => *dst = Some(b),
(Agg::SumInt(acc), Part::Int(n)) => *acc += n,
// WAIT: reply = MIN over per-shard acked counts.
(Agg::MinInt(acc), Part::Int(n)) => *acc = (*acc).min(n),
// REPL.WAIT: every shard must report 1 (met).
(Agg::ReplBarrier { ok, .. }, Part::Int(n)) => *ok &= n > 0,
// REPL.TOKEN: pairs drop in by shard id.
(Agg::ReplTokens { slots }, Part::ReplToken { shard, generation, next_offset }) => {
if let Some(s) = slots.get_mut(shard as usize) {
*s = Some((generation, next_offset));
}
}
(Agg::AllOk, Part::Ok) => {}
(Agg::ExtensionGather { chunks, .. }, Part::ExtensionChunk(c)) => {
chunks.push(c);
}
(Agg::ClientList { text }, Part::ExtensionChunk(c)) => {
text.extend_from_slice(&c);
}
(Agg::ClientKill { killed, .. }, Part::Int(n)) => *killed += n,
(Agg::Gather { got, .. }, Part::Gathered(items))
| (Agg::ZStoreGather { got, .. }, Part::Gathered(items)) => {
for (k, g) in items {
got.insert(k, g);
}
}
// Geo *STORE step 1: the source shard's search result.
(Agg::GeoStore { hits, .. }, Part::GeoHits(h)) => *hits = Some(h),
(Agg::Keys { acc, .. }, Part::Keys(ks)) => acc.extend(ks),
// Weighted reservoir: candidate i survives with probability
// live_i / seen, which makes every key in the whole keyspace
// exactly equally likely — a big shard's candidate wins more
// often precisely because it stands for more keys. The shard's
// own `draw` supplies the coin, so the fold stays a pure
// (agg, part) function.
// An empty shard's candidate is None — absorbed, weight zero.
// It gets its own arm because the mismatch fallthrough below
// treats an unpaired (agg, part) as a routing bug.
(Agg::RandomKey { .. }, Part::RandomKey { key: None, .. }) => {}
(Agg::RandomKey { key, seen }, Part::RandomKey { key: Some(k), live, draw }) => {
*seen += live.max(1);
if key.is_none() || kevy_rng_below(draw, *seen) < live.max(1) {
*key = Some(k);
}
}
// SCAN page: bank the keys, remember the shard's next
// cursor, debit the COUNT work budget; the decision
// (reply vs chain into the next shard) happens in
// `finalize_scan_agg` once the slot completes.
(
Agg::ScanPage { keys, next, budget, .. },
Part::ScanPage { next: n, keys: ks, visited },
) => {
keys.extend(ks);
*next = n;
*budget = budget.saturating_sub(visited);
}
(Agg::PrefixStats { keys, expires }, Part::PrefixStats { keys: k, expires: e }) => {
*keys += k;
*expires += e;
}
(Agg::SlowlogGet { entries, .. }, Part::SlowlogEntries(es)) => {
entries.extend(es);
}
(Agg::WatchCollect { pairs }, Part::WatchVersions(items)) => {
pairs.extend(items);
}
// Cross-shard XREAD gather: drop each stream's element into
// its request-order slot.
(Agg::XReadGather { slots }, Part::XReadElement { index, element }) => {
if let Some(slot) = slots.get_mut(index as usize) {
*slot = element;
}
}
(Agg::ExecPrep { dirty, .. }, Part::Int(n)) => *dirty |= n != 0,
// Cross-shard RENAME orchestrator: buffer the step-1
// result in the agg so finalize can ship step 2.
(Agg::RenameOrchestrator { taken, .. }, Part::RenameTaken { value, ttl_ms }) => {
*taken = Some((value, ttl_ms))
}
// Step 2's put result: `refused = None` → stored; `Some`
// → NX-blocked, and the handed-back value lands in `taken`
// so finalize can restore src before the `:0` reply.
(
Agg::RenameOrchestrator { put_stored, taken, .. },
Part::RenamePutDone { refused },
) => {
*put_stored = Some(refused.is_none());
if refused.is_some() {
*taken = refused;
}
}
(Agg::BitOpGather { got, .. }, Part::Gathered(pairs)) => {
got.extend(pairs);
}
// Cross-shard COPY: step 1's clone, then step 2's verdict.
(Agg::CopyOrchestrator { read, .. }, Part::CopyRead(r)) => *read = Some(r),
(Agg::CopyOrchestrator { stored, .. }, Part::CopyPutDone { stored: st }) => {
*stored = Some(st);
}
// Cross-shard list move: buffer each step's result in the agg
// so finalize can decide the next hop.
(Agg::ListMoveOrchestrator { taken, .. }, Part::ListMoveTaken(r)) => {
*taken = Some(r)
}
(Agg::ListMoveOrchestrator { pushed, .. }, Part::ListMovePushed { refused }) => {
*pushed = Some(refused.is_none())
}
// The terminal step-1 miss (RenameNoSuchSrc) leaves
// `taken == None`; finalize reads that as "missing src".
_ => {}
}
slot.remaining -= 1;
if slot.remaining == 0 {
let proto = slot.proto;
let agg = std::mem::replace(&mut slot.agg, Agg::AllOk);
if matches!(
agg,
Agg::WatchCollect { .. }
| Agg::ExecPrep { .. }
| Agg::RenameOrchestrator { .. }
| Agg::ListMoveOrchestrator { .. }
| Agg::CopyOrchestrator { .. }
| Agg::BitOpGather { .. }
| Agg::ZStoreGather { .. }
| Agg::GeoStore { .. }
| Agg::ExtensionGather { .. }
| Agg::ScanPage { .. }
) {
Some(agg)
} else {
slot.done = Some(materialize(agg, proto));
drain_front(conn);
None
}
} else {
None
}
};
if let Some(agg) = watch_agg {
match agg {
Agg::WatchCollect { .. } | Agg::ExecPrep { .. } => {
self.finalize_watch_agg(conn_id, seq, agg);
}
Agg::RenameOrchestrator { .. } => self.finalize_rename_agg(conn_id, seq, agg),
Agg::ListMoveOrchestrator { .. } => self.finalize_list_move_agg(conn_id, seq, agg),
Agg::CopyOrchestrator { .. } => self.finalize_copy_agg(conn_id, seq, agg),
Agg::BitOpGather { .. } => self.finalize_bitop_agg(conn_id, seq, agg),
Agg::ZStoreGather { .. } => self.finalize_zstore_agg(conn_id, seq, agg),
Agg::GeoStore { .. } => self.finalize_geostore_agg(conn_id, seq, agg),
Agg::ScanPage { .. } => self.finalize_scan_agg(conn_id, seq, agg),
Agg::ExtensionGather { argv, chunks } => {
let proto =
self.conns.get(&conn_id).map_or(kevy_resp::RespVersion::V2, |c| c.proto);
match self.commands.extension_reduce(&argv, chunks, proto) {
crate::ExtensionReduced::Reply(reply) => {
self.fill_extension_slot(conn_id, seq, reply);
}
// Phase state rides inside the follow-up argv
// itself (stateless two-phase, no new agg
// variant).
crate::ExtensionReduced::Continue(argv2) => {
self.start_extension_phase(conn_id, seq, argv2);
}
}
}
// The match above is exhaustive over what fold ever puts
// into `watch_agg` (only the orchestrator aggs). Anything
// else is a bug; ignore so a stray slot doesn't crash
// the reactor.
_ => {}
}
}
}
pub(crate) fn protocol_error(&mut self, conn_id: u64) {
let seq = match self.conns.get_mut(&conn_id) {
Some(c) => {
let s = c.next_seq;
c.next_seq += 1;
c.closing = true;
let proto = c.proto;
c.pending.push_back(PendingSlot {
remaining: 1,
agg: Agg::First(None),
done: None,
proto,
});
s
}
None => return,
};
self.fold(conn_id, seq, Part::Reply(SmallReply::from_slice(b"-ERR Protocol error\r\n")));
}
}
/// Does `args` set a TTL via a *relative* duration (vs absolute `*AT`)? Such
/// writes need an absolute `PEXPIREAT` follow-up in the AOF — see
/// [`Shard::log_write`]. `SET … EXAT|PXAT` aren't parsed by the server's SET,
/// so only `EX`/`PX` count here.
pub(crate) fn relative_ttl_write<A: ArgvView + ?Sized>(args: &A) -> bool {
if args.len() < 3 {
return false;
}
let verb = &args[0];
if verb.eq_ignore_ascii_case(b"EXPIRE")
|| verb.eq_ignore_ascii_case(b"PEXPIRE")
|| verb.eq_ignore_ascii_case(b"SETEX")
|| verb.eq_ignore_ascii_case(b"PSETEX")
{
return true;
}
if verb.eq_ignore_ascii_case(b"SET") {
return (3..args.len())
.any(|i| args[i].eq_ignore_ascii_case(b"EX") || args[i].eq_ignore_ascii_case(b"PX"));
}
false
}
/// Uniform in `0..n` from one raw draw (Lemire's multiply-shift, no rejection).
/// The residual bias is under one part in 2^64/n — invisible at keyspace sizes.
fn kevy_rng_below(draw: u64, n: u64) -> u64 {
if n <= 1 {
return 0;
}
((u128::from(draw) * u128::from(n)) >> 64) as u64
}