fix: remove num_build_thread param (#39340)

issue: #39090 
The num_build_thread parameter will limit the number of build omps. This
parameter will override the effect of buildIndexThreadPoolRatio.
Removing this parameter will have no actual effect. This parameter is
actually only used in the growing index, where it will be explicitly
set.

Signed-off-by: xianliang.li <xianliang.li@zilliz.com>

pkg/util/paramtable/knowhere_param.go

@@ -2,7 +2,6 @@ package paramtable
 
 import (
 	"fmt"
-	"strconv"
 	"strings"
 
 	"github.com/milvus-io/milvus-proto/go-api/v2/commonpb"
@@ -22,7 +21,6 @@ const (
 
 const (
 	BuildDramBudgetKey = "build_dram_budget_gb"
-	NumBuildThreadKey  = "num_build_thread"
 	VecFieldSizeKey    = "vec_field_size_gb"
 )
 
@@ -89,7 +87,6 @@ func (p *knowhereConfig) GetRuntimeParameter(stage string) (map[string]string, e
 
 	if stage == BuildStage {
 		params[BuildDramBudgetKey] = fmt.Sprintf("%f", float32(hardware.GetFreeMemoryCount())/(1<<30))
-		params[NumBuildThreadKey] = strconv.Itoa(int(float32(hardware.GetCPUNum())))
 	}
 
 	return params, nil

pkg/util/paramtable/knowhere_param_test.go

@@ -82,7 +82,6 @@ func TestKnowhereConfig_GetRuntimeParameter(t *testing.T) {
 	params, err := cfg.GetRuntimeParameter(BuildStage)
 	assert.NoError(t, err)
 	assert.Contains(t, params, BuildDramBudgetKey)
-	assert.Contains(t, params, NumBuildThreadKey)
 
 	params, err = cfg.GetRuntimeParameter(SearchStage)
 	assert.NoError(t, err)
@@ -208,7 +207,6 @@ func TestKnowhereConfig_MergeWithResource(t *testing.T) {
 			expectedParams: map[string]string{
 				"existing_key":     "existing_value",
 				BuildDramBudgetKey: "", // We can't predict the exact value, but it should exist
-				NumBuildThreadKey:  "", // We can't predict the exact value, but it should exist
 				VecFieldSizeKey:    "1.000000",
 			},
 		},