fix: use seperate warmup pool and disable warmup by default (#33348)

1. use a small warmup pool to reduce the impact of warmup
2. change the warmup pool to nonblocking mode
3. disable warmup by default
4. remove the maximum size limit of 16 for the load pool

issue: https://github.com/milvus-io/milvus/issues/32772

---------

Signed-off-by: bigsheeper <yihao.dai@zilliz.com>
Co-authored-by: xiaofanluan <xiaofan.luan@zilliz.com>

configs/milvus.yaml

@@ -335,7 +335,7 @@ queryNode:
     # chunk cache during the load process. This approach has the potential to substantially reduce query/search latency
     # for a specific duration post-load, albeit accompanied by a concurrent increase in disk usage;
     # 2. If set to "off," original vector data will only be loaded into the chunk cache during search/query.
-    warmup: async
+    warmup: off
   mmap:
     mmapEnabled: false # Enable mmap for loading data
   lazyload:

internal/querynodev2/segments/pool.go

@@ -37,12 +37,14 @@ var (
 	// and other operations (insert/delete/statistics/etc.)
 	// since in concurrent situation, there operation may block each other in high payload
 
-	sqp      atomic.Pointer[conc.Pool[any]]
-	sqOnce   sync.Once
-	dp       atomic.Pointer[conc.Pool[any]]
-	dynOnce  sync.Once
-	loadPool atomic.Pointer[conc.Pool[any]]
-	loadOnce sync.Once
+	sqp        atomic.Pointer[conc.Pool[any]]
+	sqOnce     sync.Once
+	dp         atomic.Pointer[conc.Pool[any]]
+	dynOnce    sync.Once
+	loadPool   atomic.Pointer[conc.Pool[any]]
+	loadOnce   sync.Once
+	warmupPool atomic.Pointer[conc.Pool[any]]
+	warmupOnce sync.Once
 )
 
 // initSQPool initialize
@@ -80,9 +82,6 @@ func initLoadPool() {
 	loadOnce.Do(func() {
 		pt := paramtable.Get()
 		poolSize := hardware.GetCPUNum() * pt.CommonCfg.MiddlePriorityThreadCoreCoefficient.GetAsInt()
-		if poolSize > 16 {
-			poolSize = 16
-		}
 		pool := conc.NewPool[any](
 			poolSize,
 			conc.WithPreAlloc(false),
@@ -96,6 +95,23 @@ func initLoadPool() {
 	})
 }
 
+func initWarmupPool() {
+	warmupOnce.Do(func() {
+		pt := paramtable.Get()
+		poolSize := hardware.GetCPUNum() * pt.CommonCfg.LowPriorityThreadCoreCoefficient.GetAsInt()
+		pool := conc.NewPool[any](
+			poolSize,
+			conc.WithPreAlloc(false),
+			conc.WithDisablePurge(false),
+			conc.WithPreHandler(runtime.LockOSThread), // lock os thread for cgo thread disposal
+			conc.WithNonBlocking(true),                // make warming up non blocking
+		)
+
+		warmupPool.Store(pool)
+		pt.Watch(pt.CommonCfg.LowPriorityThreadCoreCoefficient.Key, config.NewHandler("qn.warmpool.lowpriority", ResizeWarmupPool))
+	})
+}
+
 // GetSQPool returns the singleton pool instance for search/query operations.
 func GetSQPool() *conc.Pool[any] {
 	initSQPool()
@@ -113,6 +129,11 @@ func GetLoadPool() *conc.Pool[any] {
 	return loadPool.Load()
 }
 
+func GetWarmupPool() *conc.Pool[any] {
+	initWarmupPool()
+	return warmupPool.Load()
+}
+
 func ResizeSQPool(evt *config.Event) {
 	if evt.HasUpdated {
 		pt := paramtable.Get()
@@ -131,6 +152,14 @@ func ResizeLoadPool(evt *config.Event) {
 	}
 }
 
+func ResizeWarmupPool(evt *config.Event) {
+	if evt.HasUpdated {
+		pt := paramtable.Get()
+		newSize := hardware.GetCPUNum() * pt.CommonCfg.LowPriorityThreadCoreCoefficient.GetAsInt()
+		resizePool(GetWarmupPool(), newSize, "WarmupPool")
+	}
+}
+
 func resizePool(pool *conc.Pool[any], newSize int, tag string) {
 	log := log.Ctx(context.Background()).
 		With(

internal/querynodev2/segments/pool_test.go

@@ -82,6 +82,27 @@ func TestResizePools(t *testing.T) {
 		assert.Equal(t, expectedCap, GetLoadPool().Cap())
 	})
 
+	t.Run("WarmupPool", func(t *testing.T) {
+		expectedCap := hardware.GetCPUNum() * pt.CommonCfg.LowPriorityThreadCoreCoefficient.GetAsInt()
+
+		ResizeWarmupPool(&config.Event{
+			HasUpdated: true,
+		})
+		assert.Equal(t, expectedCap, GetWarmupPool().Cap())
+
+		pt.Save(pt.CommonCfg.LowPriorityThreadCoreCoefficient.Key, strconv.FormatFloat(pt.CommonCfg.LowPriorityThreadCoreCoefficient.GetAsFloat()*2, 'f', 10, 64))
+		ResizeWarmupPool(&config.Event{
+			HasUpdated: true,
+		})
+		assert.Equal(t, expectedCap, GetWarmupPool().Cap())
+
+		pt.Save(pt.CommonCfg.LowPriorityThreadCoreCoefficient.Key, "0")
+		ResizeWarmupPool(&config.Event{
+			HasUpdated: true,
+		})
+		assert.Equal(t, expectedCap, GetWarmupPool().Cap())
+	})
+
 	t.Run("error_pool", func(*testing.T) {
 		pool := conc.NewDefaultPool[any]()
 		c := pool.Cap()

internal/querynodev2/segments/segment.go

@@ -1386,7 +1386,7 @@ func (s *LocalSegment) WarmupChunkCache(ctx context.Context, fieldID int64) {
 	warmingUp := strings.ToLower(paramtable.Get().QueryNodeCfg.ChunkCacheWarmingUp.GetValue())
 	switch warmingUp {
 	case "sync":
-		GetLoadPool().Submit(func() (any, error) {
+		GetWarmupPool().Submit(func() (any, error) {
 			cFieldID := C.int64_t(fieldID)
 			status = C.WarmupChunkCache(s.ptr, cFieldID)
 			if err := HandleCStatus(ctx, &status, "warming up chunk cache failed"); err != nil {
@@ -1397,7 +1397,7 @@ func (s *LocalSegment) WarmupChunkCache(ctx context.Context, fieldID int64) {
 			return nil, nil
 		}).Await()
 	case "async":
-		GetLoadPool().Submit(func() (any, error) {
+		GetWarmupPool().Submit(func() (any, error) {
 			if !s.ptrLock.RLockIf(state.IsNotReleased) {
 				return nil, nil
 			}

pkg/util/paramtable/component_param.go

@@ -2357,7 +2357,7 @@ func (p *queryNodeConfig) init(base *BaseTable) {
 	p.ChunkCacheWarmingUp = ParamItem{
 		Key:          "queryNode.cache.warmup",
 		Version:      "2.3.6",
-		DefaultValue: "async",
+		DefaultValue: "off",
 		Doc: `options: async, sync, off. 
 Specifies the necessity for warming up the chunk cache. 
 1. If set to "sync" or "async," the original vector data will be synchronously/asynchronously loaded into the 

pkg/util/paramtable/component_param_test.go

@@ -339,7 +339,7 @@ func TestComponentParam(t *testing.T) {
 
 		// chunk cache
 		assert.Equal(t, "willneed", Params.ReadAheadPolicy.GetValue())
-		assert.Equal(t, "async", Params.ChunkCacheWarmingUp.GetValue())
+		assert.Equal(t, "false", Params.ChunkCacheWarmingUp.GetValue())
 
 		// test small indexNlist/NProbe default
 		params.Remove("queryNode.segcore.smallIndex.nlist")