feat(spooler): Implement backpressure in spooler via bounded queues

relay-config/src/config.rs

@@ -912,6 +912,11 @@ fn spool_disk_usage_refresh_frequency_ms() -> u64 {
     100
 }
 
+/// Default bounded buffer size for handling backpressure.
+fn spool_max_backpressure_envelopes() -> usize {
+    500
+}
+
 /// Persistent buffering configuration for incoming envelopes.
 #[derive(Debug, Serialize, Deserialize)]
 pub struct EnvelopeSpool {
@@ -955,6 +960,9 @@ pub struct EnvelopeSpool {
     /// internal page stats.
     #[serde(default = "spool_disk_usage_refresh_frequency_ms")]
     disk_usage_refresh_frequency_ms: u64,
+    /// The amount of envelopes that can be put in the bounded buffer.
+    #[serde(default = "spool_max_backpressure_envelopes")]
+    max_backpressure_envelopes: usize,
     /// Version of the spooler.
     #[serde(default)]
     version: EnvelopeSpoolVersion,
@@ -991,6 +999,7 @@ impl Default for EnvelopeSpool {
             max_batches: spool_envelopes_stack_max_batches(),
             max_envelope_delay_secs: spool_envelopes_max_envelope_delay_secs(),
             disk_usage_refresh_frequency_ms: spool_disk_usage_refresh_frequency_ms(),
+            max_backpressure_envelopes: spool_max_backpressure_envelopes(),
             version: EnvelopeSpoolVersion::default(),
         }
     }
@@ -2212,6 +2221,11 @@ impl Config {
         Duration::from_millis(self.values.spool.envelopes.disk_usage_refresh_frequency_ms)
     }
 
+    /// Returns the maximum number of envelopes that can be put in the bounded buffer.
+    pub fn spool_max_backpressure_envelopes(&self) -> usize {
+        self.values.spool.envelopes.max_backpressure_envelopes
+    }
+
     /// Returns the maximum size of an event payload in bytes.
     pub fn max_event_size(&self) -> usize {
         self.values.limits.max_event_size.as_bytes()

relay-server/src/service.rs

@@ -3,9 +3,6 @@ use std::fmt;
 use std::sync::Arc;
 use std::time::Duration;
 
-use crate::metrics::{MetricOutcomes, MetricStats};
-use crate::services::buffer::{self, EnvelopeBufferService, ObservableEnvelopeBuffer};
-use crate::services::stats::RelayStats;
 use anyhow::{Context, Result};
 use axum::extract::FromRequestParts;
 use axum::http::request::Parts;
@@ -15,7 +12,10 @@ use relay_config::{Config, RedisConnection, RedisPoolConfigs};
 use relay_redis::{RedisConfigOptions, RedisError, RedisPool, RedisPools};
 use relay_system::{channel, Addr, Service};
 use tokio::runtime::Runtime;
+use tokio::sync::mpsc;
 
+use crate::metrics::{MetricOutcomes, MetricStats};
+use crate::services::buffer::{self, EnvelopeBufferService, ObservableEnvelopeBuffer};
 use crate::services::cogs::{CogsService, CogsServiceRecorder};
 use crate::services::global_config::{GlobalConfigManager, GlobalConfigService};
 use crate::services::health_check::{HealthCheck, HealthCheckService};
@@ -25,6 +25,7 @@ use crate::services::outcome_aggregator::OutcomeAggregator;
 use crate::services::processor::{self, EnvelopeProcessor, EnvelopeProcessorService};
 use crate::services::project_cache::{ProjectCache, ProjectCacheService, Services};
 use crate::services::relays::{RelayCache, RelayCacheService};
+use crate::services::stats::RelayStats;
 #[cfg(feature = "processing")]
 use crate::services::store::StoreService;
 use crate::services::test_store::{TestStore, TestStoreService};
@@ -241,11 +242,13 @@ impl ServiceState {
         )
         .spawn_handler(processor_rx);
 
+        let (envelopes_tx, envelopes_rx) = mpsc::channel(config.spool_max_backpressure_envelopes());
         let envelope_buffer = EnvelopeBufferService::new(
             config.clone(),
             MemoryChecker::new(memory_stat.clone(), config.clone()),
             global_config_rx.clone(),
             buffer::Services {
+                envelopes_tx,
                 project_cache: project_cache.clone(),
                 outcome_aggregator: outcome_aggregator.clone(),
                 test_store: test_store.clone(),
@@ -269,6 +272,7 @@ impl ServiceState {
             MemoryChecker::new(memory_stat.clone(), config.clone()),
             project_cache_services,
             global_config_rx,
+            envelopes_rx,
             redis_pools
                 .as_ref()
                 .map(|pools| pools.project_configs.clone()),