bench: what screening costs while catching up

Review 2, N7, measured first: a node whose document has no policy (a
joiner's empty one) applies what it receives unjudged. Screening it too
would cost finding every change's paths and judging it. bench_screening
takes 1 000, 10 000 and 100 000 changes into an empty document, as one
delta brings them: unjudged, as Automerge applies them, against
screened (access::screen::apply), with no policy in them (each passes,
read at its dependencies, after its paths were found) and with the
policy their first change wrote (each judged by the rules).

2 files changed, 110 insertions, 2 deletions

diff --git a/docs/development.md b/docs/development.md
index 2fb7ab5..85f6fce 100644
--- a/docs/development.md
+++ b/docs/development.md
@@ -19,8 +19,8 @@ nor arti; among Mycelium's tests is a swarm simulated on its envelope).
 
 The benchmarks are ignored tests named `bench_*`: the document's (writes and sync
 messages, what signing and checking every change would cost: `bench_change_signatures`,
-and knowing every change's paths: `bench_change_paths`;
-`document/bench.rs`), the remakes' replay (`remake/bench.rs`), and what
+knowing every change's paths: `bench_change_paths`, and judging every change while
+catching up: `bench_screening`; `document/bench.rs`), the remakes' replay (`remake/bench.rs`), and what
 passing changes on costs over the simulated network (`simtest/bench.rs`: messages and
 bytes per write by kind, propagation delays, for a full mesh, a writer behind NAT (in a full mesh, and in a partial one), two
 transports, partial meshes of 50 and 100 nodes, lossy links (with delays at random,
diff --git a/src/document/bench.rs b/src/document/bench.rs
index bc1f6fa..467dc2f 100644
--- a/src/document/bench.rs
+++ b/src/document/bench.rs
@@ -29,6 +29,13 @@
 //! rebuilds them, and from the bytes they came as; and inspected before they are
 //! applied (`inspect::Inspector`), their objects made among them or looked up in the
 //! document, each once.
+//!
+//! `screening`: what judging every change received costs while catching up
+//! (`access::screen`), against applying them unjudged, as a node whose document has no
+//! policy does now: many changes into an empty document, as one delta brings them;
+//! judged with no policy in them (each passes, read at its dependencies, after its
+//! paths were found), and with the policy their first change wrote (each judged by the
+//! rules).
 
 use std::time::{Duration, Instant};
 
@@ -607,3 +614,104 @@ fn bench_change_paths() {
         );
     }
 }
+
+/// `changes` changes on `doc`, each writing `servers/<region>/<n>/cpu`, by `actors`
+/// actors in turn, as `nested` does.
+fn nested_on(mut doc: Document, changes: usize, actors: usize) -> Document {
+    let per = changes.div_ceil(actors.max(1));
+    for i in 0..changes {
+        if i % per == 0 {
+            doc.set_actor(automerge::ActorId::random());
+        }
+        let path = [
+            "servers".to_owned(),
+            format!("region{}", i % 4),
+            format!("{}", (i / 4) % 50),
+            "cpu".to_owned(),
+        ];
+        transact(&mut doc, UnixMillis(1), &WRITER, |doc| {
+            store::write_path(doc, &path, &serde_json::json!(i))
+        })
+        .expect("write");
+    }
+    doc
+}
+
+/// The time to take `doc`'s changes into an empty document: unjudged, as Automerge
+/// applies them; and screened (`access::screen::apply`).
+fn screening_costs(workload: &str, doc: &Document) {
+    let raw: Vec<Vec<u8>> = doc
+        .get_changes(&[])
+        .iter()
+        .map(|change| change.raw_bytes().to_vec())
+        .collect();
+    let changes = || -> Vec<automerge::Change> {
+        raw.iter()
+            .map(|bytes| automerge::Change::from_bytes(bytes.clone()).expect("change"))
+            .collect()
+    };
+    let unjudged = median(3, || {
+        let changes = changes();
+        let mut empty = Document::new();
+        let started = Instant::now();
+        empty.apply_changes(changes).expect("apply");
+        started.elapsed()
+    });
+    let screened = median(3, || {
+        let changes = changes();
+        let mut empty = Document::new();
+        let started = Instant::now();
+        let screened = crate::access::screen::apply(
+            &mut empty,
+            Epoch::GENESIS,
+            changes,
+            &mut crate::access::screen::Waiting::default(),
+            &mut crate::access::screen::Refusals::default(),
+            None,
+            &mut crate::document::PatchLog::inactive(),
+        )
+        .expect("screen");
+        let elapsed = started.elapsed();
+        assert_eq!(screened.applied, raw.len(), "every change taken");
+        elapsed
+    });
+    report_signatures(
+        workload,
+        unjudged,
+        &[("screened", screened.saturating_sub(unjudged))],
+    );
+}
+
+#[test]
+#[ignore = "a benchmark: cargo benchmarks"]
+fn bench_screening() {
+    println!();
+    for changes in [1_000, 10_000, 100_000] {
+        screening_costs(
+            &format!("{changes} changes, no policy"),
+            &nested(changes, changes / 100),
+        );
+        // The swarm, its policy and the writer's member entry first: every change after
+        // is judged by the rules (no registry: the writer's node, a member, may).
+        let mut start = Document::new();
+        transact(&mut start, UnixMillis(1), &WRITER, |doc| {
+            let path = |text: &str| -> Vec<String> { text.split('/').map(str::to_owned).collect() };
+            store::write_path(doc, &path("_continuum/swarm"), &serde_json::json!("bench"))?;
+            store::write_path(
+                doc,
+                &path("_continuum/access/policy"),
+                &serde_json::json!({"version": 1}),
+            )?;
+            store::write_path(
+                doc,
+                &crate::swarm::members::member_path(WRITER.node),
+                &serde_json::json!({}),
+            )
+        })
+        .expect("start");
+        screening_costs(
+            &format!("{changes} changes, the policy first"),
+            &nested_on(start, changes, changes / 100),
+        );
+    }
+}