feat: Concurrent KV event consumer (#7293)

Signed-off-by: jthomson04 <jwillthomson19@gmail.com>

lib/kv-router/src/indexer/kv_indexer.rs

@@ -18,6 +18,74 @@ use crate::indexer::pruning::{BlockEntry, PruneConfig, PruneManager};
 use crate::protocols::*;
 use dynamo_tokens::SequenceHash;
 
+fn stored_block_entries(event: &RouterEvent) -> Option<Vec<BlockEntry>> {
+    let KvCacheEventData::Stored(ref store_data) = event.event.data else {
+        return None;
+    };
+
+    let worker = WorkerWithDpRank::new(event.worker_id, event.event.dp_rank);
+    Some(
+        store_data
+            .blocks
+            .iter()
+            .enumerate()
+            .map(|(idx, block)| BlockEntry {
+                key: block.block_hash,
+                worker,
+                seq_position: idx,
+            })
+            .collect(),
+    )
+}
+
+fn apply_event_with_prune_tracking(
+    trie: &mut RadixTree,
+    event: RouterEvent,
+    metrics: &KvIndexerMetrics,
+    prune_manager: &mut Option<PruneManager<BlockEntry>>,
+    prune_tx: &mpsc::Sender<()>,
+) {
+    let event_type = KvIndexerMetrics::get_event_type(&event.event.data);
+    let event_id = event.event.event_id;
+    let worker_id = event.worker_id;
+    let event_for_prune = prune_manager.is_some().then(|| event.clone());
+    let result = trie.apply_event(event);
+    let result_is_ok = result.is_ok();
+    let tree_size = trie.current_size();
+    tracing::trace!(
+        "Applied KV event to global radix tree: event_type={event_type}, event_id={event_id}, worker_id={worker_id}, success={result_is_ok}, global_radix_tree_size={tree_size}"
+    );
+    metrics.increment_event_applied(event_type, result);
+
+    let Some(pm) = prune_manager.as_mut() else {
+        return;
+    };
+    if !result_is_ok {
+        return;
+    }
+    let Some(ref event) = event_for_prune else {
+        return;
+    };
+    let Some(block_entries) = stored_block_entries(event) else {
+        return;
+    };
+
+    pm.insert(block_entries);
+
+    let Some(ref pc) = pm.prune_config else {
+        return;
+    };
+    let current_size = trie.current_size();
+    if current_size > pc.max_tree_size {
+        tracing::info!(
+            "Pruning: tree size ({}) exceeded max tree size ({}), scheduling pruning",
+            current_size,
+            pc.max_tree_size
+        );
+        let _ = prune_tx.try_send(());
+    }
+}
+
 /// The KV Indexer, managing the KV store and handling events and match requests.
 #[derive(Clone)]
 pub struct KvIndexer {
@@ -64,7 +132,7 @@ impl KvIndexer {
         metrics: Arc<KvIndexerMetrics>,
         prune_config: Option<PruneConfig>,
     ) -> Self {
-        let (event_tx, event_rx) = mpsc::channel::<RouterEvent>(2048);
+        let (event_tx, event_rx) = mpsc::channel::<RouterEvent>(16384);
         let (match_tx, match_rx) = mpsc::channel::<MatchRequest>(128);
         let (remove_worker_tx, remove_worker_rx) = mpsc::channel::<WorkerId>(16);
         let (remove_worker_dp_rank_tx, remove_worker_dp_rank_rx) =
@@ -151,49 +219,26 @@ impl KvIndexer {
                         }
 
                         Some(event) = event_rx.recv() => {
-                            let event_type = KvIndexerMetrics::get_event_type(&event.event.data);
-                            let event_id = event.event.event_id;
-                            let worker_id = event.worker_id;
-                            // Only clone if we need the event for prune_manager afterward
-                            let event_for_prune = prune_manager.is_some().then(|| event.clone());
-                            let result = trie.apply_event(event);
-                            let result_is_ok = result.is_ok();
-                            let tree_size = trie.current_size();
-                            tracing::trace!(
-                                "Applied KV event to global radix tree: event_type={event_type}, event_id={event_id}, worker_id={worker_id}, success={result_is_ok}, global_radix_tree_size={tree_size}"
+                            apply_event_with_prune_tracking(
+                                &mut trie,
+                                event,
+                                &metrics,
+                                &mut prune_manager,
+                                &prune_tx,
                             );
-                            metrics.increment_event_applied(event_type, result);
-
-                            // Track blocks in PruneManager if TTL is enabled and event was stored successfully
-                            let Some(ref mut pm) = prune_manager else { continue };
-                            if !result_is_ok { continue };
-                            let Some(ref event) = event_for_prune else { continue };
-                            let KvCacheEventData::Stored(ref store_data) = event.event.data else { continue };
-
-                            let worker = WorkerWithDpRank::new(event.worker_id, event.event.dp_rank);
-                            let block_entries: Vec<BlockEntry> = store_data.blocks.iter().enumerate().map(|(idx, block)| {
-                                BlockEntry {
-                                    key: block.block_hash,
-                                    worker,
-                                    seq_position: idx,
                         }
-                            }).collect();
-                            pm.insert(block_entries);
 
-                            // Check if we need to prune due to tree size
-                            let Some(ref pc) = pm.prune_config else { continue };
-                            let current_size = trie.current_size();
-                            if current_size > pc.max_tree_size {
-                                tracing::info!(
-                                    "Pruning: tree size ({}) exceeded max tree size ({}), scheduling pruning",
-                                    current_size,
-                                    pc.max_tree_size
+                        Some(dump_req) = dump_rx.recv() => {
+                            // Flush pending events so tree is consistent with buffer
+                            while let Ok(event) = event_rx.try_recv() {
+                                apply_event_with_prune_tracking(
+                                    &mut trie,
+                                    event,
+                                    &metrics,
+                                    &mut prune_manager,
+                                    &prune_tx,
                                 );
-                                let _ = prune_tx.try_send(());
-                            }
                             }
-
-                        Some(dump_req) = dump_rx.recv() => {
                             let events = trie.dump_tree_as_events();
                             let _ = dump_req.resp.send(events);
                         }

lib/kv-router/src/indexer/local.rs

@@ -53,6 +53,15 @@ impl LocalKvIndexer {
         buffer.iter().cloned().collect()
     }
 
+    /// Build a tree dump response with the given `last_event_id`.
+    async fn tree_dump_response(&self, last_event_id: u64) -> WorkerKvQueryResponse {
+        let events = self.dump_events().await.unwrap_or_default();
+        WorkerKvQueryResponse::TreeDump {
+            events,
+            last_event_id,
+        }
+    }
+
     /// Query events by ID range, returning events in `[start_id, end_id]` (both inclusive).
     ///
     /// ### Arguments
@@ -63,7 +72,7 @@ impl LocalKvIndexer {
     /// ### Returns
     ///
     /// - `Events`: Buffered events with original IDs (when range is within buffer)
-    /// - `TreeDump`: Full tree dump with synthetic IDs (when range is too old or unspecified)
+    /// - `TreeDump`: Full tree dump with synthetic IDs and the worker's latest real event ID (when range is too old or unspecified)
     /// - `TooNew`: Error when requested range is newer than available data
     /// - `InvalidRange`: Error when end_id < start_id
     pub async fn get_events_in_id_range(
@@ -98,8 +107,7 @@ impl LocalKvIndexer {
         // If no start_id specified, dump entire tree
         if start_id.is_none() {
             tracing::debug!("No start_id specified, dumping entire tree");
-            let events = self.dump_events().await.unwrap_or_default();
-            return WorkerKvQueryResponse::TreeDump(events);
+            return self.tree_dump_response(last_id.unwrap_or(0)).await;
         }
 
         let start_id = start_id.unwrap();
@@ -108,8 +116,7 @@ impl LocalKvIndexer {
         // Check for empty buffer
         let Some(first_buffered) = first_id else {
             tracing::debug!("Buffer empty, dumping entire tree");
-            let events = self.dump_events().await.unwrap_or_default();
-            return WorkerKvQueryResponse::TreeDump(events);
+            return self.tree_dump_response(0).await;
         };
         let last_buffered = last_id.unwrap();
 
@@ -134,8 +141,7 @@ impl LocalKvIndexer {
                 first_buffered,
                 "Requested start_id is older than buffer, dumping entire tree"
             );
-            let events = self.dump_events().await.unwrap_or_default();
-            return WorkerKvQueryResponse::TreeDump(events);
+            return self.tree_dump_response(last_buffered).await;
         }
 
         // Serve from buffer
@@ -196,17 +202,20 @@ impl LocalKvIndexer {
 
     /// Apply event with buffering.
     ///
-    /// This records the event in the buffer and forwards it to the underlying indexer.
+    /// This forwards the event to the underlying indexer and records it on success.
     pub async fn apply_event_with_buffer(&self, event: RouterEvent) -> Result<(), KvRouterError> {
-        // Record in buffer
-        self.record_event(event.clone());
-
         // Forward to underlying indexer
-        self.indexer
+        let result = self
+            .indexer
             .event_sender()
-            .send(event)
+            .send(event.clone())
             .await
-            .map_err(|_| KvRouterError::IndexerOffline)
+            .map_err(|_| KvRouterError::IndexerOffline);
+        if result.is_ok() {
+            self.record_event(event);
+        }
+
+        result
     }
 
     /// Clear the event buffer.

lib/kv-router/src/indexer/tests.rs

@@ -1941,7 +1941,7 @@ async fn test_local_indexer_slice_within_range() {
     let extract_events = |resp: WorkerKvQueryResponse| -> Vec<RouterEvent> {
         match resp {
             WorkerKvQueryResponse::Events(e) => e,
-            WorkerKvQueryResponse::TreeDump(e) => e,
+            WorkerKvQueryResponse::TreeDump { events: e, .. } => e,
             _ => panic!("Unexpected response type"),
         }
     };
@@ -1962,7 +1962,7 @@ async fn test_local_indexer_slice_within_range() {
 
     // start_id=0 is before buffer (first is 1), so should trigger tree dump
     let result = indexer.get_events_in_id_range(Some(0), Some(4)).await;
-    assert!(matches!(result, WorkerKvQueryResponse::TreeDump(_)));
+    assert!(matches!(result, WorkerKvQueryResponse::TreeDump { .. }));
 
     let result = indexer.get_events_in_id_range(Some(3), Some(3)).await;
     let ids = get_ids(extract_events(result));
@@ -2016,7 +2016,7 @@ async fn test_local_indexer_get_events_in_id_range_all_cases() {
     let extract_events = |resp: WorkerKvQueryResponse| -> Vec<RouterEvent> {
         match resp {
             WorkerKvQueryResponse::Events(e) => e,
-            WorkerKvQueryResponse::TreeDump(e) => e,
+            WorkerKvQueryResponse::TreeDump { events: e, .. } => e,
             _ => panic!("Unexpected response type: {:?}", resp),
         }
     };
@@ -2038,11 +2038,11 @@ async fn test_local_indexer_get_events_in_id_range_all_cases() {
 
     // Tree dump path tests
     let result = indexer.get_events_in_id_range(None, None).await;
-    assert!(matches!(result, WorkerKvQueryResponse::TreeDump(_)));
+    assert!(matches!(&result, WorkerKvQueryResponse::TreeDump { .. }));
     assert_eq!(extract_events(result).len(), 10);
 
     let result = indexer.get_events_in_id_range(Some(7), None).await;
-    assert!(matches!(result, WorkerKvQueryResponse::TreeDump(_)));
+    assert!(matches!(result, WorkerKvQueryResponse::TreeDump { .. }));
 
     // Edge cases
     let result = indexer.get_events_in_id_range(Some(15), Some(10)).await;
@@ -2052,6 +2052,98 @@ async fn test_local_indexer_get_events_in_id_range_all_cases() {
     assert!(matches!(result, WorkerKvQueryResponse::TooNew { .. }));
 }
 
+#[tokio::test]
+async fn test_tree_dump_includes_last_event_id() {
+    // Create indexer with small buffer (5 events max)
+    let indexer = LocalKvIndexer::new(
+        CancellationToken::new(),
+        4,
+        Arc::new(KvIndexerMetrics::new_unregistered()),
+        5,
+    );
+
+    let make_event = |id: u64| {
+        RouterEvent::new(
+            0,
+            KvCacheEvent {
+                event_id: id,
+                data: KvCacheEventData::Stored(KvCacheStoreData {
+                    parent_hash: None,
+                    blocks: vec![KvCacheStoredBlockData {
+                        block_hash: ExternalSequenceBlockHash(id * 100),
+                        tokens_hash: LocalBlockHash(id * 200),
+                        mm_extra_info: None,
+                    }],
+                }),
+                dp_rank: 0,
+            },
+        )
+    };
+
+    // Add 10 events (IDs 5-14), buffer keeps last 5: events 10-14
+    for id in 5..15 {
+        indexer
+            .apply_event_with_buffer(make_event(id))
+            .await
+            .unwrap();
+    }
+    indexer.flush().await;
+
+    // Request with start_id=None -> tree dump should include last_event_id=14
+    let result = indexer.get_events_in_id_range(None, None).await;
+    match result {
+        WorkerKvQueryResponse::TreeDump {
+            last_event_id,
+            events,
+        } => {
+            assert_eq!(
+                last_event_id, 14,
+                "last_event_id should be the buffer's newest event ID"
+            );
+            assert!(!events.is_empty(), "tree dump should contain events");
+        }
+        other => panic!("Expected TreeDump, got: {other:?}"),
+    }
+
+    // Request with start_id older than buffer -> tree dump should include last_event_id=14
+    let result = indexer.get_events_in_id_range(Some(7), None).await;
+    match result {
+        WorkerKvQueryResponse::TreeDump {
+            last_event_id,
+            events,
+        } => {
+            assert_eq!(
+                last_event_id, 14,
+                "last_event_id should be the buffer's newest event ID"
+            );
+            assert!(!events.is_empty(), "tree dump should contain events");
+        }
+        other => panic!("Expected TreeDump, got: {other:?}"),
+    }
+
+    // Empty buffer case: create a fresh indexer with no events
+    let empty_indexer = LocalKvIndexer::new(
+        CancellationToken::new(),
+        4,
+        Arc::new(KvIndexerMetrics::new_unregistered()),
+        5,
+    );
+    let result = empty_indexer.get_events_in_id_range(None, None).await;
+    match result {
+        WorkerKvQueryResponse::TreeDump {
+            last_event_id,
+            events,
+        } => {
+            assert_eq!(
+                last_event_id, 0,
+                "empty buffer should return last_event_id=0"
+            );
+            assert!(events.is_empty(), "empty indexer should have no events");
+        }
+        other => panic!("Expected TreeDump, got: {other:?}"),
+    }
+}
+
 #[tokio::test]
 async fn test_local_indexer_buffer_and_serialization() {
     let worker_id = 42u64;
@@ -2099,6 +2191,51 @@ async fn test_local_indexer_buffer_and_serialization() {
     assert_eq!(events[0].worker_id, worker_id);
 }
 
+#[tokio::test]
+async fn test_local_indexer_does_not_buffer_failed_send() {
+    let local_indexer = LocalKvIndexer::new(
+        CancellationToken::new(),
+        4,
+        Arc::new(KvIndexerMetrics::new_unregistered()),
+        5,
+    );
+
+    let test_event = RouterEvent::new(
+        7,
+        KvCacheEvent {
+            event_id: 1,
+            data: KvCacheEventData::Stored(KvCacheStoreData {
+                parent_hash: None,
+                blocks: vec![KvCacheStoredBlockData {
+                    block_hash: ExternalSequenceBlockHash(100),
+                    tokens_hash: LocalBlockHash(200),
+                    mm_extra_info: None,
+                }],
+            }),
+            dp_rank: 0,
+        },
+    );
+
+    let event_tx = local_indexer.event_sender();
+    local_indexer.shutdown();
+    event_tx.closed().await;
+
+    let result = local_indexer.apply_event_with_buffer(test_event).await;
+    assert!(matches!(result, Err(KvRouterError::IndexerOffline)));
+    assert_eq!(local_indexer.buffer_len(), 0);
+
+    match local_indexer.get_events_in_id_range(None, None).await {
+        WorkerKvQueryResponse::TreeDump {
+            events,
+            last_event_id,
+        } => {
+            assert!(events.is_empty());
+            assert_eq!(last_event_id, 0);
+        }
+        other => panic!("Expected TreeDump, got: {other:?}"),
+    }
+}
+
 #[tokio::test]
 #[apply(indexer_template)]
 async fn test_apply_events_idempotent(variant: &str) {

lib/kv-router/src/indexer/types.rs

@@ -56,8 +56,13 @@ pub struct WorkerKvQueryRequest {
 pub enum WorkerKvQueryResponse {
     /// Events served from the circular buffer (with original event IDs)
     Events(Vec<RouterEvent>),
-    /// Full tree dump (with synthetic 0-indexed event IDs)
-    TreeDump(Vec<RouterEvent>),
+    /// Full tree dump (with synthetic 0-indexed event IDs).
+    /// Includes `last_event_id`: the newest real event ID in the worker's buffer
+    /// at the time of the dump, so the caller can set its tracking cursor correctly.
+    TreeDump {
+        events: Vec<RouterEvent>,
+        last_event_id: u64,
+    },
     /// Requested range is newer than available data
     TooNew {
         requested_start: Option<u64>,

lib/llm/src/kv_router/publisher.rs

@@ -2024,7 +2024,7 @@ mod tests_startup_helpers {
             .await;
         let missed_events = match response {
             crate::kv_router::indexer::WorkerKvQueryResponse::Events(e) => e,
-            crate::kv_router::indexer::WorkerKvQueryResponse::TreeDump(e) => e,
+            crate::kv_router::indexer::WorkerKvQueryResponse::TreeDump { events: e, .. } => e,
             crate::kv_router::indexer::WorkerKvQueryResponse::Error(message) => {
                 panic!("Unexpected error response: {message}")
             }

lib/llm/src/kv_router/subscriber.rs

 // SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::collections::HashMap;
-
 use crate::kv_router::{
-    Indexer, KV_EVENT_SUBJECT, KvRouterConfig,
-    protocols::{DpRank, RouterEvent, WorkerId},
+    Indexer, KV_EVENT_SUBJECT, KvRouterConfig, protocols::RouterEvent,
     worker_query::WorkerQueryClient,
 };
 use anyhow::Result;
@@ -23,9 +20,6 @@ use dynamo_runtime::{
 /// - On worker Added: dumps worker's local indexer into router
 /// - On worker Removed: removes worker from router indexer
 ///
-/// This function first recovers state from all currently registered workers before
-/// spawning the background task, ensuring the router is ready before returning.
-///
 /// This is appropriate when workers have local indexers enabled.
 async fn start_kv_router_background_event_plane(
     component: Component,
@@ -47,7 +41,9 @@ async fn start_kv_router_background_event_plane(
     // before recovery fetches the initial dump from workers.
     tokio::time::sleep(std::time::Duration::from_millis(100)).await;
 
-    let worker_query_client = WorkerQueryClient::spawn(component.clone(), indexer.clone()).await?;
+    // WorkerQueryClient handles its own discovery loop for lifecycle + initial recovery.
+    // No blocking wait — recovery happens asynchronously as endpoints are discovered.
+    let worker_query_client = WorkerQueryClient::spawn(component.clone(), indexer).await?;
     let kv_event_subject = format!(
         "namespace.{}.component.{}.{}",
         component.namespace().name(),
@@ -71,10 +67,6 @@ async fn start_kv_router_background_event_plane(
     }
 
     tokio::spawn(async move {
-        // Track last received event ID per (worker, dp_rank) for gap detection
-        // Each dp_rank has its own monotonic event ID sequence
-        let mut last_event_ids: HashMap<(WorkerId, DpRank), u64> = HashMap::new();
-
         loop {
             tokio::select! {
                 biased;
@@ -94,47 +86,19 @@ async fn start_kv_router_background_event_plane(
                         }
                     };
 
-                    let worker_id = event.worker_id;
-                    let dp_rank = event.event.dp_rank;
-                    let event_id = event.event.event_id;
-                    let event_key = (worker_id, dp_rank);
-
                     tracing::trace!(
                         "Received event from publisher {} (seq {})",
                         envelope.publisher_id,
                         envelope.sequence
                     );
 
-                    // Gap detection: check if event ID is monotonically increasing per (worker, dp_rank)
-                    // Note: event_id <= last_id is duplicate/out-of-order, apply anyway (idempotent)
-                    if let Some(&last_id) = last_event_ids.get(&event_key)
-                        && event_id > last_id + 1
-                    {
-                        let gap_start = last_id + 1;
-                        let gap_end = event_id - 1;
-                        let gap_size = gap_end - gap_start + 1;
-                        tracing::warn!(
-                            "Event ID gap detected for worker {worker_id} dp_rank {dp_rank}, recovering events [{gap_start}, {gap_end}], gap_size: {gap_size}"
-                        );
-
-                        if let Err(e) = worker_query_client
-                            .recover_from_worker(worker_id, dp_rank, Some(gap_start), Some(gap_end))
-                            .await
-                        {
-                            tracing::error!(
-                                "Failed to recover gap events for worker {worker_id} dp_rank {dp_rank} (gap_start: {gap_start}, gap_end: {gap_end}); proceeding with current event anyway: {e}"
+                    tracing::trace!(
+                        "Forwarding live event to recovery coordinator for worker {} dp_rank {} event_id {}",
+                        event.worker_id,
+                        event.event.dp_rank,
+                        event.event.event_id
                     );
-                        }
-                    }
-
-                    // Update last seen event ID (use max to handle out-of-order)
-                    last_event_ids
-                        .entry(event_key)
-                        .and_modify(|id| *id = (*id).max(event_id))
-                        .or_insert(event_id);
-
-                    // Forward the RouterEvent to the indexer
-                    indexer.apply_event(event).await;
+                    worker_query_client.handle_live_event(event).await;
                 }
             }
         }