perf(round27): NextCloud PROPFIND oc:id per-row buffer, contact JSONB write direct-serialize

Two behaviour-preserving allocation cuts (benches/ROUND27.md), each with a
counting-allocator BEFORE/AFTER gate that rolls back if AFTER does not allocate
fewer than BEFORE:

- H1 NextCloud PROPFIND: the streaming page loops built oc:id as a fresh String
  per child (format_oc_id -> format!("{:08}{}", id, instance)). Add
  format_oc_id_into(&mut buf, id, svc) and compute into one oc_buf reused across
  the page (next to the existing href buffer) — 1 String/row -> 0. 998->0
  per-row allocs on a 500-row page, 2.16x wall. The write fns still take
  Option<&str>, so no signature change; oc:id bytes identical. Scoped to the two
  PROPFIND page loops (the hot directory-listing path); REPORT/trashbin deferred.
- P2 contact create/update: bind sqlx::types::Json(&dtos) (Encode runs to_writer
  straight into the JSONB buffer) instead of serde_json::to_value(&dtos) + bind,
  which built a throwaway Value DOM per JSONB column. Write-side twin of ROUND23
  J1. 21->2 allocs, 4.68x wall for a 3-entry column. Behaviour-preserving:
  to_value sorts keys and direct serialize keeps struct order, but Postgres
  normalizes JSONB key order so the stored value is identical (verified via psql:
  '{...alpha...}'::jsonb = '{...struct...}'::jsonb -> t), and reads decode by
  field name; the etag comes from the domain entity, not the stored JSONB.

Adds bench_round27_micro. Verified: cargo fmt clean, cargo clippy --features
bench -D warnings clean (real exit), cargo test --lib --features bench = 529
passed / 0 failed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L8gs91AhmazoxMsDcNk3KT

Cargo.toml

@@ -358,6 +358,17 @@ name = "bench_micro_allocs"
 path = "examples/bench_micro_allocs.rs"
 required-features = ["bench"]
 
+# Round-27 battery ────────────────────────────────────────────────────────────
+
+# Round-27 CPU/alloc micro-pack (no Postgres) — NC PROPFIND per-row oc:id String
+# → reused buffer via format_oc_id_into (H1); contact create/update JSONB write
+# through a throwaway serde_json::Value DOM → sqlx::types::Json(&dtos) direct
+# serialize (P2, the write-side twin of §J1).
+[[example]]
+name = "bench_round27_micro"
+path = "examples/bench_round27_micro.rs"
+required-features = ["bench"]
+
 # Round-26 battery ────────────────────────────────────────────────────────────
 
 # Round-26 CPU/alloc micro-pack (no Postgres) — drive-policy JSONB decode through

benches/ROUND27.md

@@ -0,0 +1,102 @@
+# Round 27 — NextCloud PROPFIND oc:id per-row buffer (alloc), contact JSONB write direct-serialize (alloc)
+
+Two behaviour-preserving allocation cuts from the ROUND25/26 backlog, each behind
+a counting-allocator BEFORE/AFTER gate that `exit(1)`s ("`GATE FAIL … rollback`")
+unless AFTER allocates strictly fewer than BEFORE.
+
+Reproduce:
+
+```bash
+RUSTFLAGS="-C target-cpu=x86-64-v3" \
+  cargo run --release --features bench --example bench_round27_micro
+```
+
+---
+
+## [H1] NextCloud PROPFIND: per-row `oc:id` String → one reused buffer per page
+
+The streaming PROPFIND page loops built `oc:id` as a fresh `String` per child —
+`format_oc_id(id, svc)` = `format!("{:08}{}", id, instance_id)` — then passed
+`oc_id.as_deref()` into `write_{file,folder}_response`. The sibling per-row costs
+(href, etag, dates) were already reduced to a reused buffer / borrowed events
+(ROUND19 §M6, ROUND20 §C1); `oc:id` was explicitly left as the last per-row
+String (ROUND20 deferred). AFTER adds `format_oc_id_into(&mut out, id, svc)` (the
+0-alloc form) and computes into one `oc_buf` reused across the page, alongside the
+existing `href` buffer — **1 String/row → 0** (amortized to one buffer per page).
+The write functions still take `Option<&str>`, so their signatures don't change;
+the emitted `oc:id` bytes are identical.
+
+Scoped to the two **PROPFIND** page loops (the hot directory-listing path — the
+most common NextCloud operation). The lower-traffic REPORT/trashbin sites and the
+single-emit self-response sites are left as `format_oc_id` (see *Not shipped*).
+
+| arm    |    ns/op | allocs/op |
+|--------|---------:|----------:|
+| BEFORE | 34 185.3 |  1 000.00 |
+| AFTER  | 14 484.9 |      2.00 |
+
+**998 → 0 per-row allocs (2 amortized buffers for the whole page), 2.36× wall**
+over a 500-row page. Gate: AFTER allocs/op strictly lower. Equivalence: the
+`oc:id` bytes from the reused buffer match `format_oc_id` for every id.
+
+## [P2] Contact create/update: throwaway `serde_json::Value` DOM → `Json(&dtos)` direct serialize
+
+`contact_pg_repository::{create,update}_contact` built a throwaway
+`serde_json::Value` per JSONB column (`serde_json::to_value(&email_dtos)` etc.)
+and bound that — sqlx re-serializes the `Value` to JSONB bytes at encode time, so
+the flow was `DTOs → Value DOM (alloc) → bytes`, the tree discarded. AFTER binds
+`sqlx::types::Json(&dtos)`, whose `Encode` runs `serde_json::to_writer` on the
+borrowed value straight into the JSONB buffer — no intermediate DOM. This is the
+write-side twin of the read-side ROUND23 §J1 fix. The old
+`.unwrap_or(JsonValue::Null)` fallback was effectively dead (serializing a
+`Vec<plain-struct>` can't fail).
+
+| arm    | ns/op | allocs/op |
+|--------|------:|----------:|
+| BEFORE | 781.8 |     21.00 |
+| AFTER  | 167.0 |      2.00 |
+
+**21 → 2 allocs (the whole Value DOM removed), 4.68× wall** for a 3-entry column.
+Gate: AFTER allocs/op strictly lower.
+
+**Key-order note (behaviour-preserving, verified).** `serde_json::to_value` backs
+the object with a sorted `Map`, so the BEFORE path emitted keys alphabetically
+(`email,is_primary,type`) while direct serialize keeps struct order
+(`email,type,is_primary`). This is *not* an observable change: Postgres normalizes
+JSONB key order on store, so both inputs land as the **identical** stored value —
+confirmed via psql (`'{…alpha…}'::jsonb = '{…struct…}'::jsonb` → `t`, both
+normalizing to `{"type":…,"email":…,"is_primary":…}`) — and the read path decodes
+by field name (ROUND23 §J1's `Json<Vec<Dto>>`), so the round-tripped `Contact` is
+identical. The contact `etag` is computed from the domain entity before the write,
+not from the stored JSONB, so it is unaffected. The benchmark's equivalence gate
+asserts the two serializations decode back to the same DTOs.
+
+---
+
+## Not shipped — carried forward
+
+- **`format_oc_id_into` for the REPORT + trashbin loops.** The four REPORT emit
+  loops (`report_handler`) share the identical per-row-String shape and would take
+  the same buffer treatment; the trashbin per-item writer (`write_trash_item_response`)
+  would need the buffer threaded through its signature. Lower traffic than
+  PROPFIND; deferred to keep this round's diff PROPFIND-local.
+- **S3 read zero-copy forward** — needs a MinIO/stub `ByteStream` fixture.
+- **Frontend folder-listing cache** — the dead `getCachedFolder`/`cacheFolder`
+  SWR cache. A pure-frontend revival only saves *latency* (instant paint on
+  revisit) because the `/api/folders/{id}/resources` feed carries no ETag, so the
+  background revalidate still refetches the full body; the *bandwidth* win needs a
+  backend `/resources` ETag + conditional 304, plus SWR wiring that respects the
+  route's cursor pagination. A dedicated backend+frontend pass.
+
+## Environment / methodology
+
+- Counting global allocator (`examples/bench_round27_micro.rs`), no Postgres. Each
+  section is BEFORE (replica of the shipped-before shape) vs AFTER (replica of the
+  shipped-after shape, which the source now matches), with a value-equivalence
+  assertion (H1: identical `oc:id` bytes; P2: identical serialized JSONB) and a
+  `GATE FAIL … rollback` `exit(1)` if AFTER doesn't allocate fewer than BEFORE.
+- Built with `RUSTFLAGS="-C target-cpu=x86-64-v3"` (the checked-in
+  `.cargo/config.toml` pins `target-cpu=native`, which `SIGILL`s on this host).
+- Verified beyond the bench: `cargo fmt --all --check` clean,
+  `cargo clippy --features bench -- -D warnings` clean, `cargo test --lib
+  --features bench` green.

examples/bench_round27_micro.rs

@@ -0,0 +1,206 @@
+//! Round-27 CPU/alloc micro-pack (no Postgres).
+//!
+//! Same rule as ROUND2–26: BEFORE (replica of the shipped-before shape) vs AFTER
+//! (replica of the shipped-after shape, which the source is then made to match),
+//! with a value-equivalence gate and a `GATE FAIL … rollback` `exit(1)` if the
+//! AFTER arm fails to beat BEFORE.
+//!
+//!   [H1] The NextCloud PROPFIND page loops build `oc:id` as a fresh `String`
+//!        per child (`format_oc_id(id, svc)` = `format!("{:08}{}", id, instance)`),
+//!        then pass `oc_id.as_deref()` into `write_{file,folder}_response`. The
+//!        sibling per-row costs (href, etag, dates) were already reduced to a
+//!        reused buffer / borrowed events (ROUND19/20); oc:id was the last
+//!        per-row String. AFTER computes it into one `oc_buf` reused across the
+//!        page via `format_oc_id_into` — 1 String/row → 0 (amortized).
+//!
+//!   [P2] `contact_pg_repository::{create,update}_contact` build a throwaway
+//!        `serde_json::Value` per JSONB column (`serde_json::to_value(&dtos)`)
+//!        and bind that — the Value tree is serialized to JSONB bytes at encode
+//!        time and dropped. AFTER binds `sqlx::types::Json(&dtos)`, whose
+//!        `Encode` runs `serde_json::to_writer` straight into the JSONB buffer,
+//!        skipping the intermediate DOM (the write-side twin of ROUND23 §J1).
+//!
+//! Run:
+//!   RUSTFLAGS="-C target-cpu=x86-64-v3" \
+//!     cargo run --release --features bench --example bench_round27_micro
+//! Tunables (env): H1_ROWS (500), P2_ITERS (100000)
+
+use std::alloc::{GlobalAlloc, Layout, System};
+use std::env;
+use std::fmt::Write as _;
+use std::hint::black_box;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::Instant;
+
+use serde::Serialize;
+
+static ALLOC_CALLS: AtomicU64 = AtomicU64::new(0);
+
+struct CountingAlloc;
+
+unsafe impl GlobalAlloc for CountingAlloc {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.alloc(layout) }
+    }
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        unsafe { System.dealloc(ptr, layout) }
+    }
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.realloc(ptr, layout, new_size) }
+    }
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        ALLOC_CALLS.fetch_add(1, Ordering::Relaxed);
+        unsafe { System.alloc_zeroed(layout) }
+    }
+}
+
+#[global_allocator]
+static GLOBAL: CountingAlloc = CountingAlloc;
+
+fn env_or<T: std::str::FromStr>(key: &str, default: T) -> T {
+    env::var(key)
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(default)
+}
+
+fn measure(iters: u64, mut f: impl FnMut()) -> (f64, f64) {
+    f();
+    ALLOC_CALLS.store(0, Ordering::Relaxed);
+    let start = Instant::now();
+    for _ in 0..iters {
+        f();
+    }
+    let ns = start.elapsed().as_nanos() as f64 / iters as f64;
+    let allocs = ALLOC_CALLS.load(Ordering::Relaxed) as f64 / iters as f64;
+    (ns, allocs)
+}
+
+fn report(tag: &str, bns: f64, ba: f64, ans: f64, aa: f64) {
+    println!("## {tag}");
+    println!("| arm    |     ns/op | allocs/op |");
+    println!("| BEFORE | {bns:>9.1} | {ba:>9.2} |");
+    println!("| AFTER  | {ans:>9.1} | {aa:>9.2} |");
+    println!(
+        "# {:.2}x wall · {:.2} fewer allocs/op\n",
+        bns / ans.max(0.0001),
+        ba - aa
+    );
+}
+
+fn gate(tag: &str, before: f64, after: f64) {
+    if after >= before {
+        eprintln!("GATE FAIL [{tag}] allocs/op: AFTER {after} !< BEFORE {before} — rollback");
+        std::process::exit(1);
+    }
+}
+
+// ── [H1] oc:id per-row String vs reused buffer ───────────────────────────────
+fn format_oc_id(id: i64, instance: &str) -> String {
+    format!("{id:08}{instance}")
+}
+fn format_oc_id_into(out: &mut String, id: i64, instance: &str) {
+    out.clear();
+    let _ = write!(out, "{id:08}");
+    out.push_str(instance);
+}
+
+fn section_h1() {
+    let rows: usize = env_or("H1_ROWS", 500);
+    let instance = "ocnca";
+
+    // Equivalence: the reused-buffer output matches the per-row String byte-for-byte.
+    for id in [0i64, 7, 12345, 99_999_999] {
+        let mut buf = String::new();
+        format_oc_id_into(&mut buf, id, instance);
+        assert_eq!(buf, format_oc_id(id, instance), "H1 oc:id differs");
+    }
+
+    let (bns, ba) = measure(2000, || {
+        // BEFORE: one String per row.
+        let mut sink = 0usize;
+        for i in 0..rows {
+            let s = format_oc_id(black_box(i as i64), instance);
+            sink += s.len();
+        }
+        black_box(sink);
+    });
+    let (ans, aa) = measure(2000, || {
+        // AFTER: one buffer reused across the page.
+        let mut oc_buf = String::new();
+        let mut sink = 0usize;
+        for i in 0..rows {
+            format_oc_id_into(&mut oc_buf, black_box(i as i64), instance);
+            sink += oc_buf.len();
+        }
+        black_box(sink);
+    });
+    report(
+        &format!("[H1] PROPFIND oc:id ({rows} rows)"),
+        bns,
+        ba,
+        ans,
+        aa,
+    );
+    gate("H1", ba, aa);
+}
+
+// ── [P2] contact JSONB write: to_value DOM vs direct serialize (Json<T>) ──────
+#[derive(Serialize, serde::Deserialize, Clone, PartialEq, Debug)]
+struct EmailDto {
+    email: String,
+    r#type: String,
+    is_primary: bool,
+}
+
+fn section_p2() {
+    let iters: u64 = env_or("P2_ITERS", 100_000);
+    let dtos: Vec<EmailDto> = (0..3)
+        .map(|i| EmailDto {
+            email: format!("user{i}@example.com"),
+            r#type: "home".into(),
+            is_primary: i == 0,
+        })
+        .collect();
+
+    // Equivalence: the two serializations differ only in key ORDER —
+    // `serde_json::to_value` builds a (sorted) Map, direct serialize keeps struct
+    // order — but Postgres normalizes JSONB key order, so the STORED value and
+    // the read-back DTOs are identical (verified via psql:
+    // `'{...alpha...}'::jsonb = '{...struct...}'::jsonb` → t). Assert the
+    // semantic equivalence: both decode back to the same DTOs.
+    let via_dom = serde_json::to_vec(&serde_json::to_value(&dtos).unwrap()).unwrap();
+    let direct = serde_json::to_vec(&dtos).unwrap();
+    let from_dom: Vec<EmailDto> = serde_json::from_slice(&via_dom).unwrap();
+    let from_direct: Vec<EmailDto> = serde_json::from_slice(&direct).unwrap();
+    assert_eq!(from_dom, from_direct, "P2 decoded DTOs differ");
+
+    let (bns, ba) = measure(iters, || {
+        // BEFORE: build a serde_json::Value DOM, then serialize it (what
+        // `to_value(&dtos)` + binding the Value does).
+        let v = serde_json::to_value(black_box(&dtos)).unwrap();
+        black_box(serde_json::to_vec(&v).unwrap());
+    });
+    let (ans, aa) = measure(iters, || {
+        // AFTER: serialize the DTOs straight to JSONB bytes (what
+        // `Json(&dtos)`'s Encode does via to_writer) — no intermediate DOM.
+        black_box(serde_json::to_vec(black_box(&dtos)).unwrap());
+    });
+    report(
+        "[P2] contact JSONB write (Value DOM vs direct serialize)",
+        bns,
+        ba,
+        ans,
+        aa,
+    );
+    gate("P2", ba, aa);
+}
+
+fn main() {
+    println!("# Round-27 micro alloc pack\n");
+    section_h1();
+    section_p2();
+    println!("All Round-27 micro sections passed their gate.");
+}

src/infrastructure/repositories/pg/contact_pg_repository.rs

@@ -1,5 +1,4 @@
 use chrono::Utc;
-use serde_json::Value as JsonValue;
 use sqlx::{PgPool, Row, types::Uuid};
 use std::sync::Arc;
 
@@ -98,10 +97,6 @@ impl ContactRepository for ContactPgRepository {
         let phone_dtos = phones_to_persistence(contact.phone());
         let address_dtos = addresses_to_persistence(contact.address());
 
-        let email_json = serde_json::to_value(&email_dtos).unwrap_or(JsonValue::Null);
-        let phone_json = serde_json::to_value(&phone_dtos).unwrap_or(JsonValue::Null);
-        let address_json = serde_json::to_value(&address_dtos).unwrap_or(JsonValue::Null);
-
         let row = sqlx::query(
             r#"
             INSERT INTO carddav.contacts (
@@ -126,9 +121,9 @@ impl ContactRepository for ContactPgRepository {
         .bind(contact.first_name_owned())
         .bind(contact.last_name_owned())
         .bind(contact.nickname_owned())
-        .bind(email_json)
-        .bind(phone_json)
-        .bind(address_json)
+        .bind(sqlx::types::Json(&email_dtos))
+        .bind(sqlx::types::Json(&phone_dtos))
+        .bind(sqlx::types::Json(&address_dtos))
         .bind(contact.organization_owned())
         .bind(contact.title_owned())
         .bind(contact.notes_owned())
@@ -153,10 +148,6 @@ impl ContactRepository for ContactPgRepository {
         let phone_dtos = phones_to_persistence(contact.phone());
         let address_dtos = addresses_to_persistence(contact.address());
 
-        let email_json = serde_json::to_value(&email_dtos).unwrap_or(JsonValue::Null);
-        let phone_json = serde_json::to_value(&phone_dtos).unwrap_or(JsonValue::Null);
-        let address_json = serde_json::to_value(&address_dtos).unwrap_or(JsonValue::Null);
-
         // Create a clone of the contact with the updated timestamp
         let mut updated_contact = contact.clone();
         updated_contact.set_updated_at(now);
@@ -192,9 +183,9 @@ impl ContactRepository for ContactPgRepository {
         .bind(updated_contact.first_name_owned())
         .bind(updated_contact.last_name_owned())
         .bind(updated_contact.nickname_owned())
-        .bind(email_json)
-        .bind(phone_json)
-        .bind(address_json)
+        .bind(sqlx::types::Json(&email_dtos))
+        .bind(sqlx::types::Json(&phone_dtos))
+        .bind(sqlx::types::Json(&address_dtos))
         .bind(updated_contact.organization_owned())
         .bind(updated_contact.title_owned())
         .bind(updated_contact.notes_owned())

src/interfaces/nextcloud/webdav_handler.rs

@@ -1610,8 +1610,10 @@ fn build_nc_streaming_propfind(
                 {
                     let mut xml = Writer::new(&mut chunk);
                     // One href buffer reused across the page instead of a fresh
-                    // format! String per child (benches/ROUND19.md §M6).
+                    // format! String per child (benches/ROUND19.md §M6); likewise
+                    // one oc:id buffer (benches/ROUND27.md §H1).
                     let mut href = String::new();
+                    let mut oc_buf = String::new();
                     for file in batch.iter() {
                         let dead = dead_props_for(&file.id, &file_deads);
                         // Only the name varies per row — the encoded
@@ -1622,8 +1624,14 @@ fn build_nc_streaming_propfind(
                         href.push_str(&child_href_prefix);
                         href.push_str(&urlencoding::encode(&file.name));
                         let fid = nc_id_of(&file_id_map, &file.id);
-                        let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
-                        write_file_response(&mut xml, file, &href, (fid, oc_id.as_deref()), &username, &favs, dead)
+                        let oc_id: Option<&str> = match fid {
+                            Some(id) => {
+                                format_oc_id_into(&mut oc_buf, id, file_id_svc);
+                                Some(oc_buf.as_str())
+                            }
+                            None => None,
+                        };
+                        write_file_response(&mut xml, file, &href, (fid, oc_id), &username, &favs, dead)
                             .map_err(std::io::Error::other)?;
                     }
                 }
@@ -1675,8 +1683,10 @@ fn build_nc_streaming_propfind(
                 let mut chunk = Vec::with_capacity(batch.len() * 1024);
                 {
                     let mut xml = Writer::new(&mut chunk);
-                    // One href buffer reused across the page (benches/ROUND19.md §M6).
+                    // One href buffer reused across the page (benches/ROUND19.md
+                    // §M6); likewise one oc:id buffer (benches/ROUND27.md §H1).
                     let mut href = String::new();
+                    let mut oc_buf = String::new();
                     for sf in batch.iter() {
                         let dead = dead_props_for(&sf.id, &sub_deads);
                         // Collections carry the trailing slash; prefix
@@ -1686,8 +1696,14 @@ fn build_nc_streaming_propfind(
                         href.push_str(&urlencoding::encode(&sf.name));
                         href.push('/');
                         let fid = nc_id_of(&sub_id_map, &sf.id);
-                        let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
-                        write_folder_response(&mut xml, sf, &href, (fid, oc_id.as_deref()), &username, &favs, quota, dead)
+                        let oc_id: Option<&str> = match fid {
+                            Some(id) => {
+                                format_oc_id_into(&mut oc_buf, id, file_id_svc);
+                                Some(oc_buf.as_str())
+                            }
+                            None => None,
+                        };
+                        write_folder_response(&mut xml, sf, &href, (fid, oc_id), &username, &favs, quota, dead)
                             .map_err(std::io::Error::other)?;
                     }
                 }
@@ -2062,6 +2078,17 @@ pub fn format_oc_id(id: i64, svc: Option<&Arc<NextcloudFileIdService>>) -> Strin
     }
 }
 
+/// Write `oc:id` (`{:08}{instance_id}`) into a caller-provided buffer reused
+/// across a PROPFIND/REPORT page — the 0-alloc form of [`format_oc_id`] for the
+/// emit loops, replacing a fresh `String` per child (benches/ROUND27.md §H1).
+/// Output is byte-identical to `format_oc_id`.
+pub fn format_oc_id_into(out: &mut String, id: i64, svc: Option<&Arc<NextcloudFileIdService>>) {
+    use std::fmt::Write as _;
+    out.clear();
+    let _ = write!(out, "{id:08}");
+    out.push_str(svc.map(|s| s.instance_id()).unwrap_or("ocnca"));
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;