From 8e2c307bdb501db0ab0ce2d51bc61b552855ee11 Mon Sep 17 00:00:00 2001 From: Stefan Boberg Date: Mon, 23 Mar 2026 12:54:14 +0100 Subject: Unique session/client tracking using HyperLogLog (#884) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Summary Adds probabilistic cardinality estimation for tracking unique HTTP clients and sessions using a HyperLogLog implementation. - Add a `HyperLogLog` template in `zentelemetry` with thread-safe lock-free register updates, merge support, and XXH3 hashing - Feed client IP addresses (via raw bytes) and session IDs (via `Oid` bytes) into their respective HyperLogLog estimators from both the ASIO and http.sys server backends - Emit `distinct_clients` and `distinct_sessions` cardinality estimates in HTTP `CollectStats()` - Add tests covering empty, single, duplicates, accuracy, merge, and clear scenarios ## Why HyperLogLog Tracking exact unique counts would require storing every observed IP or session ID. HyperLogLog provides a memory-bounded probabilistic estimate (~1–2% error) using only a few KB of memory regardless of traffic volume. --- src/zenhttp/httpserver.cpp | 3 +++ 1 file changed, 3 insertions(+) (limited to 'src/zenhttp/httpserver.cpp') diff --git a/src/zenhttp/httpserver.cpp b/src/zenhttp/httpserver.cpp index e5cfbcbae..a46c5b851 100644 --- a/src/zenhttp/httpserver.cpp +++ b/src/zenhttp/httpserver.cpp @@ -988,6 +988,9 @@ HttpServer::CollectStats() } Cbo.EndObject(); + Cbo << "distinct_clients" << m_ClientAddresses.Count(); + Cbo << "distinct_sessions" << m_ClientSessions.Count(); + Cbo.BeginObject("websockets"); { Cbo << "active_connections" << GetActiveWebSocketConnectionCount(); -- cgit v1.2.3