From 9d81609a89f37649310f632bc92e879217610200 Mon Sep 17 00:00:00 2001
From: David Herberth <david.herberth@sentry.io>
Date: Tue, 6 Aug 2024 09:46:24 +0200
Subject: [PATCH] check revision after loading

---
 relay-server/src/services/project_redis.rs | 42 +++++++++++++---------
 relay-server/src/statsd.rs                 |  2 ++
 2 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/relay-server/src/services/project_redis.rs b/relay-server/src/services/project_redis.rs
index 7013e5eee51..97d44d61936 100644
--- a/relay-server/src/services/project_redis.rs
+++ b/relay-server/src/services/project_redis.rs
@@ -91,25 +91,33 @@ impl RedisProjectSource {
             .query(&mut connection)
             .map_err(RedisError::Redis)?;
 
-        let response = match raw_response_opt {
-            Some(response) => {
-                metric!(
-                    counter(RelayCounters::ProjectStateRedis) += 1,
-                    hit = "project_config"
-                );
-                let parsed = parse_redis_response(response.as_slice())?;
-                ProjectState::from(parsed)
-            }
-            None => {
-                metric!(
-                    counter(RelayCounters::ProjectStateRedis) += 1,
-                    hit = "false"
-                );
-                ProjectState::Pending
-            }
+        let Some(response) = raw_response_opt else {
+            metric!(
+                counter(RelayCounters::ProjectStateRedis) += 1,
+                hit = "false"
+            );
+            return Ok(Some(ProjectState::Pending));
         };
 
-        Ok(Some(response))
+        let response = ProjectState::from(parse_redis_response(response.as_slice())?);
+
+        // If we were passed a revision, check if we just loaded the same revision from Redis.
+        //
+        // We always want to keep the old revision alive if possible, since the already loaded
+        // version has a few caches already initialized.
+        if revision.is_some() && response.revision() == revision {
+            metric!(
+                counter(RelayCounters::ProjectStateRedis) += 1,
+                hit = "project_config_revision"
+            );
+            Ok(None)
+        } else {
+            metric!(
+                counter(RelayCounters::ProjectStateRedis) += 1,
+                hit = "project_config"
+            );
+            Ok(Some(response))
+        }
     }
 
     fn get_redis_project_config_key(&self, key: ProjectKey) -> String {
diff --git a/relay-server/src/statsd.rs b/relay-server/src/statsd.rs
index 85b55dab763..1113d528fc8 100644
--- a/relay-server/src/statsd.rs
+++ b/relay-server/src/statsd.rs
@@ -651,6 +651,8 @@ pub enum RelayCounters {
     ///  - `hit`: One of:
     ///     - `revision`: the cached version was validated to be up to date using its revision.
     ///     - `project_config`: the request was handled by the cache.
+    ///     - `project_config_revision`: the request was handled by the cache and the revision did
+    ///        not change.
     ///     - `false`: the request will be sent to the sentry endpoint.
     #[cfg(feature = "processing")]
     ProjectStateRedis,