enhance: limit the max pool size to 16 (#30371) (#30415)

according to our benchmark, concurrency level 16 is enough to fully
utilize the object storage network bandwidth
pr: #30371

Signed-off-by: yah01 <yang.cen@zilliz.com>

internal/core/src/storage/ThreadPool.h

@@ -41,10 +41,13 @@ class ThreadPool {
         max_threads_size_ = CPU_NUM * thread_core_coefficient;
 
         // only IO pool will set large limit, but the CPU helps nothing to IO operations,
-        // we need to limit the max thread num, each thread will download 16 MiB data,
-        // it should be not greater than 256 (4GiB data) to avoid OOM and send too many requests to object storage
-        if (max_threads_size_ > 256) {
-            max_threads_size_ = 256;
+        // we need to limit the max thread num, each thread will download 16~64 MiB data,
+        // according to our benchmark, 16 threads is enough to saturate the network bandwidth.
+        if (min_threads_size_ > 16) {
+            min_threads_size_ = 16;
+        }
+        if (max_threads_size_ > 16) {
+            max_threads_size_ = 16;
         }
         LOG_SEGCORE_INFO_ << "Init thread pool:" << name_
                           << " with min worker num:" << min_threads_size_

internal/querynodev2/segments/pool.go

@@ -71,8 +71,13 @@ func initDynamicPool() {
 
 func initLoadPool() {
 	loadOnce.Do(func() {
+		pt := paramtable.Get()
+		poolSize := hardware.GetCPUNum() * pt.CommonCfg.MiddlePriorityThreadCoreCoefficient.GetAsInt()
+		if poolSize > 16 {
+			poolSize = 16
+		}
 		pool := conc.NewPool[any](
-			hardware.GetCPUNum()*paramtable.Get().CommonCfg.MiddlePriorityThreadCoreCoefficient.GetAsInt(),
+			poolSize,
 			conc.WithPreAlloc(false),
 			conc.WithDisablePurge(false),
 			conc.WithPreHandler(runtime.LockOSThread), // lock os thread for cgo thread disposal