perf(mobile): merge only enough small verified-name batches to fill one

At the four-partial cap, retire the smallest partial batches only until
the new subjects fill a batch (at least one when they would leave a
partial of their own), instead of re-reading every partial.

Replace a batch whose subject was evicted and tracked again before the
sync, so its check mark and any pruned cached head are restored.

Co-authored-by: studio <dc2fc481343672df31a689840c09299972e704dac592e0da6f18486646a7ee3e@localhost>
Signed-off-by: Tom Brow <tomb@squareup.com>

mobile/lib/shared/verified_profiles/verified_profile_directory.dart

@@ -21,13 +21,18 @@ const _discoveryRefresh = Duration(minutes: 5);
 /// tolerated, a flood before EOSE fails the batch instead of buffering it.
 const _maxEarlyPerSubject = 4;
 
-/// Batches smaller than [verifiedProfileBatchSize] allowed before they are
+/// Batches smaller than [verifiedProfileBatchSize] allowed before the smallest
-/// merged into full ones.
+/// are merged into the next new one until it fills a batch.
 const _maxPartialBatches = 4;
 
 class _Batch {
-  _Batch(this.subjects);
+  _Batch(this.subjects, this.interest);
   final List<String> subjects;
+
+  /// The newest interest when the batch opened. A subject whose interest is
+  /// newer was evicted and tracked again since, which dropped its `_checked`
+  /// mark and maybe its cached head, so the batch must be read again.
+  final int interest;
   final List<NostrEvent> early = [];
 
   /// Live events awaiting proof, newest per subject, so a fast stream cannot
@@ -284,14 +289,19 @@ class VerifiedProfilesNotifier extends Notifier<Map<String, VerifiedProfile>> {
       _publish();
       return;
     }
-    // Keep every open batch whose subjects are all still tracked, so newly
+    // Keep every open batch whose subjects are all still tracked since it
-    // tracked people get a batch of their own instead of re-reading everyone
+    // opened, so newly tracked people get a batch of their own instead of
-    // already checked. A retried batch is replaced so a fresh snapshot can
+    // re-reading everyone already checked. A retried batch is replaced so a
-    // prove absence, and a batch that lost a subject to eviction is replaced
+    // fresh snapshot can prove absence, and a batch that lost a subject to
-    // too.
+    // eviction is replaced too, even if the subject was tracked again.
     for (final id in _batches.keys.toList()) {
       final batch = _batches[id]!;
-      if (!batch.stale && batch.subjects.every(_wanted.containsKey)) continue;
+      if (!batch.stale &&
+          batch.subjects.every(
+            (subject) => (_wanted[subject] ?? 1 << 62) <= batch.interest,
+          )) {
+        continue;
+      }
       _close(id);
     }
     var uncovered = _uncoveredSubjects();
@@ -300,14 +310,28 @@ class VerifiedProfilesNotifier extends Notifier<Map<String, VerifiedProfile>> {
       _publish();
       return;
     }
-    // Small additions each open a small batch. Past a few of those, merge
+    // Small additions each open a small batch. Past a few of those, merge the
-    // them into full ones, so the subscription count stays near the minimum.
+    // smallest into the new subjects until they fill a batch, so the
+    // subscription count stays near the minimum while re-reading as few
+    // checked subjects as possible.
     final partial = [
-      for (final MapEntry(:key, :value) in _batches.entries)
+      for (final batch in _batches.entries)
-        if (value.subjects.length < verifiedProfileBatchSize) key,
+        if (batch.value.subjects.length < verifiedProfileBatchSize) batch,
     ];
     if (partial.length >= _maxPartialBatches) {
-      partial.forEach(_close);
+      partial.sort(
+        (a, b) => a.value.subjects.length.compareTo(b.value.subjects.length),
+      );
+      // Retire at least one unless the new subjects split evenly, since
+      // they can add a partial batch of their own.
+      var size = uncovered.length;
+      var retired = size % verifiedProfileBatchSize == 0;
+      for (final MapEntry(:key, :value) in partial) {
+        if (retired && size >= verifiedProfileBatchSize) break;
+        size += value.subjects.length;
+        retired = true;
+        _close(key);
+      }
       uncovered = _uncoveredSubjects();
     }
     for (var i = 0; i < uncovered.length; i += verifiedProfileBatchSize) {
@@ -342,7 +366,7 @@ class VerifiedProfilesNotifier extends Notifier<Map<String, VerifiedProfile>> {
     VerifiedProfileAuthority authority,
     int generation,
   ) async {
-    final batch = _Batch(chunk);
+    final batch = _Batch(chunk, _interest);
     _batches[id] = batch;
     void fail() {
       if (!batch.active) return;

mobile/test/shared/verified_profiles/verified_profile_directory_test.dart

@@ -226,23 +226,41 @@ void main() {
     expect(h.profiles[subjectB]?.checked, isTrue);
   });
 
-  journey('small batches merge into one past four', (h) {
+  journey('past four small batches, the smallest merge until one is full', (h) {
     String key(int i) => i.toRadixString(16).padLeft(64, '0');
-    h.start([key(0)]);
     final notifier = h.container.read(verifiedProfilesProvider.notifier);
+    h.start([for (var i = 0; i < 64; i++) key(i)]);
+    for (var group = 1; group < 4; group++) {
+      notifier.track([for (var i = 0; i < 64; i++) key(group * 64 + i)]);
+      h.settle();
+    }
+    final before = h.dFilters.length;
+    expect(before, 4, reason: 'four partial batches of 64');
+    notifier.track([key(256)]);
+    h.settle();
+    // Two of the 64s fill one batch with the newcomer; the other two stay.
+    final reads = [
+      for (final f in h.dFilters.skip(before)) (f['#d'] as List).cast<String>(),
+    ];
+    expect([for (final r in reads) r.length], [128, 1]);
+    expect(reads.expand((r) => r), contains(key(256)));
+  });
+
+  journey('a large addition past four small batches still retires one', (h) {
+    String key(int i) => i.toRadixString(16).padLeft(64, '0');
+    final notifier = h.container.read(verifiedProfilesProvider.notifier);
+    h.start([key(0)]);
     for (var i = 1; i < 4; i++) {
       notifier.track([key(i)]);
       h.settle();
     }
     final before = h.dFilters.length;
-    expect(before, 4);
+    notifier.track([for (var i = 4; i < 133; i++) key(i)]);
-    notifier.track([key(4)]);
     h.settle();
+    // 129 newcomers would leave a fifth partial; one single folds in.
     expect(
-      [for (final f in h.dFilters.skip(before)) f['#d']],
+      [for (final f in h.dFilters.skip(before)) (f['#d'] as List).length],
-      [
+      [128, 2],
-        [for (var i = 0; i < 5; i++) key(i)],
-      ],
     );
   });
 
@@ -261,6 +279,44 @@ void main() {
     );
   });
 
+  journey('a subject evicted and tracked again before the sync is re-read', (
+    h,
+  ) {
+    String key(int i) => i.toRadixString(16).padLeft(64, '0');
+    h.relay.seed([signedProjection(profileTags(subjectA))]);
+    h.start([subjectA]);
+    final notifier = h.container.read(verifiedProfilesProvider.notifier);
+    notifier.track([for (var i = 0; i < 1023; i++) key(i)]);
+    h.settle();
+    expect(h.profiles[subjectA]?.checked, isTrue);
+    // A is evicted, then tracked again, which evicts key(0) in another batch.
+    notifier
+      ..track([key(1023)])
+      ..track([subjectA]);
+    h.settle();
+    expect(h.profiles[subjectA]?.checked, isTrue);
+  });
+
+  journey('a re-tracked subject keeps its name when the head cache trims', (h) {
+    String key(int i) => i.toRadixString(16).padLeft(64, '0');
+    h.relay.seed([signedProjection(profileTags(subjectA))]);
+    h.start([subjectA]);
+    final notifier = h.container.read(verifiedProfilesProvider.notifier);
+    // Each round evicts A, may trim its cached head, then tracks it again
+    // before the sync; past 4,096 cached heads only a re-read restores it.
+    for (var round = 0; round < 6; round++) {
+      final subjects = [for (var i = 0; i < 1023; i++) key(round * 1023 + i)];
+      h.relay.seed([
+        for (final s in subjects) signedProjection(profileTags(s)),
+      ]);
+      notifier
+        ..track(subjects)
+        ..track([subjectA]);
+      h.settle();
+      expect(h.profiles[subjectA]?.displayName, 'Ada Lovelace');
+    }
+  });
+
   journey('a large roster keeps the 1,024 most recently tracked subjects', (h) {
     String key(int i) => i.toRadixString(16).padLeft(64, '0');
     h.start([for (var i = 0; i < 10; i++) key(i)]);