ref(project-cache): Check revision before loading from Redis

relay-server/src/services/project.rs

@@ -310,7 +310,11 @@ impl Project {
                 "project {} state requested {attempts} times",
                 self.project_key
             );
-            project_cache.send(RequestUpdate::new(self.project_key, no_cache));
+            project_cache.send(RequestUpdate {
+                project_key: self.project_key,
+                no_cache,
+                cached_state: self.state.clone(),
+            });
         }
 
         channel
@@ -473,7 +477,11 @@ impl Project {
                 self.project_key
             );
 
-            project_cache.send(RequestUpdate::new(self.project_key, no_cache));
+            project_cache.send(RequestUpdate {
+                project_key: self.project_key,
+                no_cache,
+                cached_state: self.state.clone(),
+            });
             return old_state;
         }
 

relay-server/src/services/project/state/fetch_state.rs

@@ -25,13 +25,22 @@ impl ProjectFetchState {
         }
     }
 
+    /// Refreshes the expiry of the fetch state.
+    pub fn refresh(old: ProjectFetchState) -> Self {
+        Self {
+            last_fetch: Some(Instant::now()),
+            state: old.state,
+        }
+    }
+
     /// Project state for an unknown but allowed project.
     ///
     /// This state is used for forwarding in Proxy mode.
     pub fn allowed() -> Self {
         Self::enabled(ProjectInfo {
             project_id: None,
             last_change: None,
+            rev: None,
             public_keys: Default::default(),
             slug: None,
             config: ProjectConfig::default(),
@@ -119,6 +128,15 @@ impl ProjectFetchState {
             Expiry::Updated
         }
     }
+
+    /// Returns the revision of the contained project state.
+    pub fn revision(&self) -> Option<&str> {
+        match &self.state {
+            ProjectState::Enabled(info) => info.rev.as_deref(),
+            ProjectState::Disabled => None,
+            ProjectState::Pending => None,
+        }
+    }
 }
 
 /// Wrapper for a project state, with expiry information.

relay-server/src/services/project/state/info.rs

@@ -30,8 +30,9 @@ pub struct ProjectInfo {
     ///
     /// This might be `None` in some rare cases like where states
     /// are faked locally.
-    #[serde(default)]
     pub last_change: Option<DateTime<Utc>>,
+    /// The revision id of the project config.
+    pub rev: Option<String>,
     /// Indicates that the project is disabled.
     /// A container of known public keys in the project.
     ///
@@ -56,6 +57,7 @@ pub struct ProjectInfo {
 pub struct LimitedProjectInfo {
     pub project_id: Option<ProjectId>,
     pub last_change: Option<DateTime<Utc>>,
+    pub rev: Option<String>,
     pub public_keys: SmallVec<[PublicKeyConfig; 1]>,
     pub slug: Option<String>,
     #[serde(with = "LimitedProjectConfig")]

relay-server/src/services/project_cache.rs

@@ -53,19 +53,15 @@ use crate::utils::{GarbageDisposal, ManagedEnvelope, MemoryChecker, RetryBackoff
 #[derive(Clone, Debug)]
 pub struct RequestUpdate {
     /// The public key to fetch the project by.
-    project_key: ProjectKey,
-
+    pub project_key: ProjectKey,
     /// If true, all caches should be skipped and a fresh state should be computed.
-    no_cache: bool,
-}
-
-impl RequestUpdate {
-    pub fn new(project_key: ProjectKey, no_cache: bool) -> Self {
-        Self {
-            project_key,
-            no_cache,
-        }
-    }
+    pub no_cache: bool,
+    /// Previously cached fetch state, if availabled.
+    ///
+    /// The upstream request will include the revision of the currently cached state,
+    /// if the upstream does not have a different revision, this cached
+    /// state is re-used and its expiry bumped.
+    pub cached_state: ProjectFetchState,
 }
 
 /// Returns the project state.
@@ -459,7 +455,12 @@ impl ProjectSource {
         }
     }
 
-    async fn fetch(self, project_key: ProjectKey, no_cache: bool) -> Result<ProjectFetchState, ()> {
+    async fn fetch(
+        self,
+        project_key: ProjectKey,
+        no_cache: bool,
+        _cached_state: ProjectFetchState,
+    ) -> Result<ProjectFetchState, ()> {
         let state_opt = self
             .local_source
             .send(FetchOptionalProjectState { project_key })
@@ -479,27 +480,34 @@ impl ProjectSource {
 
         #[cfg(feature = "processing")]
         if let Some(redis_source) = self.redis_source {
+            let revision = _cached_state.revision().map(String::from);
+
             let redis_permit = self.redis_semaphore.acquire().await.map_err(|_| ())?;
-            let state_fetch_result =
-                tokio::task::spawn_blocking(move || redis_source.get_config(project_key))
-                    .await
-                    .map_err(|_| ())?;
+            let state_fetch_result = tokio::task::spawn_blocking(move || {
+                redis_source.get_config_if_changed(project_key, revision.as_deref())
+            })
+            .await
+            .map_err(|_| ())?;
             drop(redis_permit);
 
-            let state = match state_fetch_result {
-                Ok(state) => state.sanitized(),
+            match state_fetch_result {
+                // New state fetched from Redis, possibly pending.
+                Ok(Some(state)) => {
+                    let state = state.sanitized();
+                    if !state.is_pending() {
+                        return Ok(ProjectFetchState::new(state));
+                    }
+                }
+                // Redis reported that we're holding an up to date version of the state alread,
+                // refresh the state and return the old cached state again.
+                Ok(None) => return Ok(ProjectFetchState::refresh(_cached_state)),
                 Err(error) => {
                     relay_log::error!(
                         error = &error as &dyn Error,
                         "failed to fetch project from Redis",
                     );
-                    ProjectState::Pending
                 }
             };
-
-            if !matches!(state, ProjectState::Pending) {
-                return Ok(ProjectFetchState::new(state));
-            }
         };
 
         self.upstream_source
@@ -734,6 +742,7 @@ impl ProjectCacheBroker {
         let RequestUpdate {
             project_key,
             no_cache,
+            cached_state,
         } = message;
 
         // Bump the update time of the project in our hashmap to evade eviction.
@@ -750,14 +759,14 @@ impl ProjectCacheBroker {
                 tokio::time::sleep_until(next_attempt).await;
             }
             let state = source
-                .fetch(project_key, no_cache)
+                .fetch(project_key, no_cache, cached_state)
                 .await
                 .unwrap_or_else(|()| ProjectFetchState::disabled());
 
             let message = UpdateProjectState {
                 project_key,
-                state,
                 no_cache,
+                state,
             };
 
             sender.send(message).ok();

relay-server/src/services/project_redis.rs

@@ -52,19 +52,41 @@ impl RedisProjectSource {
         RedisProjectSource { config, redis }
     }
 
-    pub fn get_config(&self, key: ProjectKey) -> Result<ProjectState, RedisProjectError> {
-        let mut command = relay_redis::redis::cmd("GET");
-
-        let prefix = self.config.projectconfig_cache_prefix();
-        command.arg(format!("{prefix}:{key}"));
+    pub fn get_config_if_changed(
+        &self,
+        key: ProjectKey,
+        revision: Option<&str>,
+    ) -> Result<Option<ProjectState>, RedisProjectError> {
+        let mut client = self.redis.client()?;
+        let mut connection = client.connection()?;
+
+        // Only check for the revision if we were passed a revision.
+        if let Some(revision) = revision {
+            let current_revision: Option<String> = relay_redis::redis::cmd("GET")
+                .arg(self.get_redis_rev_key(key))
+                .query(&mut connection)
+                .map_err(RedisError::Redis)?;
+
+            if current_revision.as_deref() == Some(revision) {
+                metric!(
+                    counter(RelayCounters::ProjectStateRedis) += 1,
+                    hit = "revision",
+                );
+                return Ok(None);
+            }
+        }
 
-        let raw_response_opt: Option<Vec<u8>> = command
-            .query(&mut self.redis.client()?.connection()?)
+        let raw_response_opt: Option<Vec<u8>> = relay_redis::redis::cmd("GET")
+            .arg(self.get_redis_project_config_key(key))
+            .query(&mut connection)
             .map_err(RedisError::Redis)?;
 
         let response = match raw_response_opt {
             Some(response) => {
-                metric!(counter(RelayCounters::ProjectStateRedis) += 1, hit = "true");
+                metric!(
+                    counter(RelayCounters::ProjectStateRedis) += 1,
+                    hit = "project_config"
+                );
                 let parsed = parse_redis_response(response.as_slice())?;
                 ProjectState::from(parsed)
             }
@@ -77,7 +99,17 @@ impl RedisProjectSource {
             }
         };
 
-        Ok(response)
+        Ok(Some(response))
+    }
+
+    fn get_redis_project_config_key(&self, key: ProjectKey) -> String {
+        let prefix = self.config.projectconfig_cache_prefix();
+        format!("{prefix}:{key}")
+    }
+
+    fn get_redis_rev_key(&self, key: ProjectKey) -> String {
+        let prefix = self.config.projectconfig_cache_prefix();
+        format!("{prefix}:{key}.rev")
     }
 }
 

relay-server/src/statsd.rs

@@ -647,8 +647,11 @@ pub enum RelayCounters {
     ProjectStateNoCache,
     /// Number of times a project state is requested from the central Redis cache.
     ///
-    /// This has a tag `hit` with values `true` or `false`.  If false the request will be
-    /// sent to the sentry endpoint.
+    /// This metric is tagged with:
+    ///  - `hit`: One of:
+    ///     - `revision`: the in cached version was validated with the revision.
+    ///     - `project_config`: the request was handled by the cache.
+    ///     - `false`: the request will be sent to the sentry endpoint.
     #[cfg(feature = "processing")]
     ProjectStateRedis,
     /// Number of times a project is looked up from the cache.