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Avoid conversation index rebuilds at retention cap (#1435)

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Replaces ConversationStore's message-ID->physical-index map with logical indexes plus a head indexOffset, so cap-eviction advances the offset instead of rebuilding the whole dictionary on every steady-state append (~23.7x measured ingest throughput at cap). Adds a steady-state benchmark floor and a 1,200-op differential stress test against an O(n) reference model.
This commit is contained in:
jack
2026-07-26 10:52:28 +02:00
committed by GitHub
parent 565d2b7773
commit 400ac4c904
4 changed files with 527 additions and 26 deletions
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bitchat/App/ConversationStore.swift
+41 -25
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@@ -39,15 +39,17 @@ final class Conversation: ObservableObject, Identifiable {
@Published private(set) var messages: [BitchatMessage] = []
@Published private(set) var isUnread: Bool = false
/// Incrementally-maintained message-ID → index map for O(1) dedup and
/// delivery-status lookup. Kept in sync on every mutation:
/// - tail append: single insert
/// - out-of-order insert: suffix reindex from the insertion point
/// - trim: full rebuild — `removeFirst(k)` is already O(n), so the
/// rebuild does not change the asymptotics, and trim only happens once
/// the cap (1337) is reached. Simple and correct beats the
/// offset-tracking alternative here.
/// Incrementally-maintained message-ID → logical-index map for O(1)
/// dedup and delivery-status lookup. Logical indexes are physical array
/// indexes plus `indexOffset`; trimming from the head advances the offset
/// instead of rewriting every surviving dictionary entry. This matters
/// after the 1337-message cap is reached, when every steady-state tail
/// append evicts one old row.
///
/// Out-of-order inserts and middle removals still reindex only the
/// affected suffix. Full filtering resets the offset while rebuilding.
private var indexByMessageID: [String: Int] = [:]
private var indexOffset = 0
fileprivate init(id: ConversationID, cap: Int) {
self.id = id
@@ -61,7 +63,7 @@ final class Conversation: ObservableObject, Identifiable {
}
func message(withID messageID: String) -> BitchatMessage? {
guard let index = indexByMessageID[messageID] else { return nil }
guard let index = physicalIndex(forMessageID: messageID) else { return nil }
return messages[index]
}
@@ -101,7 +103,7 @@ final class Conversation: ObservableObject, Identifiable {
reindex(from: index)
} else {
messages.append(message)
indexByMessageID[message.id] = messages.count - 1
indexByMessageID[message.id] = indexOffset + messages.count - 1
}
return InsertResult(inserted: true, trimmedMessageIDs: trimIfNeeded())
@@ -111,7 +113,7 @@ final class Conversation: ObservableObject, Identifiable {
/// timeline position (in-place updates like media progress reuse the
/// original timestamp); a new message goes through ordered insertion.
fileprivate func upsert(_ message: BitchatMessage) -> UpsertOutcome {
if let index = indexByMessageID[message.id] {
if let index = physicalIndex(forMessageID: message.id) {
messages[index] = message
return .updated
}
@@ -125,7 +127,7 @@ final class Conversation: ObservableObject, Identifiable {
/// `.read` is never downgraded to `.delivered` or `.sent`.
/// Returns `true` when the status was applied.
fileprivate func applyDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
guard let index = indexByMessageID[messageID] else { return false }
guard let index = physicalIndex(forMessageID: messageID) else { return false }
let message = messages[index]
guard !Self.shouldSkipStatusUpdate(current: message.deliveryStatus, new: status) else { return false }
@@ -142,7 +144,7 @@ final class Conversation: ObservableObject, Identifiable {
/// observers still need an @Published emission to re-render.
@discardableResult
fileprivate func republishMessage(withID messageID: String) -> Bool {
guard let index = indexByMessageID[messageID] else { return false }
guard let index = physicalIndex(forMessageID: messageID) else { return false }
messages[index] = messages[index]
return true
}
@@ -157,10 +159,14 @@ final class Conversation: ObservableObject, Identifiable {
/// Removes a single message by ID. Returns the removed message, or
/// `nil` when no message with that ID exists.
fileprivate func remove(messageID: String) -> BitchatMessage? {
guard let index = indexByMessageID[messageID] else { return nil }
guard let index = physicalIndex(forMessageID: messageID) else { return nil }
let removed = messages.remove(at: index)
indexByMessageID.removeValue(forKey: messageID)
reindex(from: index)
if index == 0 {
indexOffset += 1
} else {
reindex(from: index)
}
return removed
}
@@ -177,6 +183,7 @@ final class Conversation: ObservableObject, Identifiable {
for id in removedIDs {
indexByMessageID.removeValue(forKey: id)
}
indexOffset = 0
reindex(from: 0)
return removedIDs
}
@@ -184,6 +191,7 @@ final class Conversation: ObservableObject, Identifiable {
fileprivate func clearMessages() {
messages.removeAll()
indexByMessageID.removeAll()
indexOffset = 0
}
// MARK: Diagnostics
@@ -205,9 +213,10 @@ final class Conversation: ObservableObject, Identifiable {
let message = messages[position]
// Count equality + every message resolving to its own position
// proves the index is exactly the inverse map (no stale extras).
if let index = indexByMessageID[message.id] {
if index != position {
violations.append("\(label): message \(message.id.prefix(8))… at \(position) indexed at \(index)")
if let logicalIndex = indexByMessageID[message.id] {
let expectedIndex = indexOffset + position
if logicalIndex != expectedIndex {
violations.append("\(label): message \(message.id.prefix(8))… at \(position) indexed at \(logicalIndex - indexOffset)")
}
} else {
violations.append("\(label): message \(message.id.prefix(8))… at \(position) missing from index")
@@ -269,10 +278,17 @@ final class Conversation: ObservableObject, Identifiable {
private func reindex(from start: Int) {
for index in start..<messages.count {
indexByMessageID[messages[index].id] = index
indexByMessageID[messages[index].id] = indexOffset + index
}
}
private func physicalIndex(forMessageID messageID: String) -> Int? {
guard let logicalIndex = indexByMessageID[messageID] else { return nil }
let index = logicalIndex - indexOffset
guard messages.indices.contains(index) else { return nil }
return index
}
/// Trims oldest messages over the cap; returns the trimmed message IDs.
private func trimIfNeeded() -> [String] {
guard messages.count > cap else { return [] }
@@ -282,7 +298,7 @@ final class Conversation: ObservableObject, Identifiable {
indexByMessageID.removeValue(forKey: id)
}
messages.removeFirst(overflow)
reindex(from: 0)
indexOffset += overflow
return trimmedIDs
}
}
@@ -844,8 +860,8 @@ extension Conversation {
/// (positions 0 and 1 swap their index entries). Requires >= 2 messages.
func _testCorruptIndexEntries() {
guard messages.count >= 2 else { return }
indexByMessageID[messages[0].id] = 1
indexByMessageID[messages[1].id] = 0
indexByMessageID[messages[0].id] = indexOffset + 1
indexByMessageID[messages[1].id] = indexOffset
}
/// Drops a message's index entry entirely (count mismatch + missing).
@@ -859,8 +875,8 @@ extension Conversation {
func _testCorruptOrderingPreservingIndex() {
guard messages.count >= 2 else { return }
messages.swapAt(0, messages.count - 1)
indexByMessageID[messages[0].id] = 0
indexByMessageID[messages[messages.count - 1].id] = messages.count - 1
indexByMessageID[messages[0].id] = indexOffset
indexByMessageID[messages[messages.count - 1].id] = indexOffset + messages.count - 1
}
}
@@ -900,7 +916,7 @@ extension ConversationStore {
extension Conversation {
fileprivate func _testAppendBypassingTrim(_ message: BitchatMessage) {
messages.append(message)
indexByMessageID[message.id] = messages.count - 1
indexByMessageID[message.id] = indexOffset + messages.count - 1
}
}
#endif