diff --git a/oomagent/server.go b/oomagent/server.go
index 334d20b8d..a3c784e6a 100644
--- a/oomagent/server.go
+++ b/oomagent/server.go
@@ -2,9 +2,11 @@ package main
 
 import (
 	"context"
+	"encoding/csv"
 	"fmt"
 	"io"
 	"log"
+	"os"
 	"time"
 
 	"google.golang.org/grpc/codes"
@@ -14,6 +16,7 @@ import (
 	"github.com/oom-ai/oomstore/pkg/errdefs"
 	"github.com/oom-ai/oomstore/pkg/oomstore"
 	"github.com/oom-ai/oomstore/pkg/oomstore/types"
+	"github.com/spf13/cast"
 )
 
 type server struct {
@@ -292,18 +295,55 @@ func (s *server) ChannelJoin(stream codegen.OomAgent_ChannelJoinServer) error {
 }
 
 func (s *server) Join(ctx context.Context, req *codegen.JoinRequest) (*codegen.JoinResponse, error) {
-	err := s.oomstore.Join(ctx, types.JoinOpt{
-		FeatureNames:   req.Features,
-		InputFilePath:  req.InputFile,
-		OutputFilePath: req.OutputFile,
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	joinResult, err := s.oomstore.Join(ctx, types.JoinOpt{
+		FeatureNames:  req.Features,
+		InputFilePath: req.InputFile,
 	})
 	if err != nil {
 		return nil, internalError(err.Error())
 	}
 
+	if err := writeJoinResultToFile(req.OutputFile, joinResult); err != nil {
+		return nil, wrapErr(err)
+	}
+
 	return &codegen.JoinResponse{}, nil
 }
 
+func writeJoinResultToFile(outputFilePath string, joinResult *types.JoinResult) error {
+	file, err := os.Create(outputFilePath)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	w := csv.NewWriter(file)
+	defer w.Flush()
+
+	if err := w.Write(joinResult.Header); err != nil {
+		return err
+	}
+	for row := range joinResult.Data {
+		if row.Error != nil {
+			return row.Error
+		}
+		if err := w.Write(joinRecord(row.Record)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func joinRecord(row []interface{}) []string {
+	record := make([]string, 0, len(row))
+	for _, value := range row {
+		record = append(record, cast.ToString(value))
+	}
+	return record
+}
+
 func (s *server) ChannelExport(req *codegen.ChannelExportRequest, stream codegen.OomAgent_ChannelExportServer) error {
 	if len(req.Features) == 0 {
 		return nil
diff --git a/oomcli/cmd/join_helper.go b/oomcli/cmd/join_helper.go
index 236c987e7..0391d9e6b 100644
--- a/oomcli/cmd/join_helper.go
+++ b/oomcli/cmd/join_helper.go
@@ -22,15 +22,9 @@ func join(ctx context.Context, store *oomstore.OomStore, opt JoinOpt, output str
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	entityRows, header, err := oomstore.GetEntityRowsFromInputFile(ctx, opt.InputFilePath)
-	if err != nil {
-		return err
-	}
-
-	joinResult, err := store.ChannelJoin(ctx, types.ChannelJoinOpt{
-		JoinFeatureNames:    opt.FeatureNames,
-		EntityRows:          entityRows,
-		ExistedFeatureNames: header[2:],
+	joinResult, err := store.Join(ctx, types.JoinOpt{
+		FeatureNames:  opt.FeatureNames,
+		InputFilePath: opt.InputFilePath,
 	})
 	if err != nil {
 		return err
diff --git a/pkg/oomstore/join.go b/pkg/oomstore/join.go
index bb6adc5de..a925f6330 100644
--- a/pkg/oomstore/join.go
+++ b/pkg/oomstore/join.go
@@ -9,8 +9,6 @@ import (
 	"sort"
 	"strconv"
 
-	"github.com/spf13/cast"
-
 	"github.com/oom-ai/oomstore/internal/database/offline"
 	"github.com/oom-ai/oomstore/pkg/errdefs"
 	"github.com/oom-ai/oomstore/pkg/oomstore/types"
@@ -73,31 +71,24 @@ func (s *OomStore) ChannelJoin(ctx context.Context, opt types.ChannelJoinOpt) (*
 }
 
 // Join gets point-in-time correct feature values for each entity row.
-// The method is similar to Join, except that both input and output are files on disk.
+// The method is similar to ChannelJoin, except a input files on disk.
 // Input File should contain header, the first two columns of Input File should be
 // entity_key, unix_milli, then followed by other real-time feature values.
-func (s *OomStore) Join(ctx context.Context, opt types.JoinOpt) error {
-	ctx, cancel := context.WithCancel(ctx)
-	defer cancel()
-
+func (s *OomStore) Join(ctx context.Context, opt types.JoinOpt) (*types.JoinResult, error) {
 	if err := util.ValidateFullFeatureNames(opt.FeatureNames...); err != nil {
-		return err
+		return nil, err
 	}
 
-	entityRows, header, err := GetEntityRowsFromInputFile(ctx, opt.InputFilePath)
+	entityRows, header, err := getEntityRowsFromInputFile(ctx, opt.InputFilePath)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
-	joinResult, err := s.ChannelJoin(ctx, types.ChannelJoinOpt{
+	return s.ChannelJoin(ctx, types.ChannelJoinOpt{
 		JoinFeatureNames:    opt.FeatureNames,
 		EntityRows:          entityRows,
 		ExistedFeatureNames: header[2:],
 	})
-	if err != nil {
-		return err
-	}
-	return writeJoinResultToFile(opt.OutputFilePath, joinResult)
 }
 
 func (s *OomStore) buildRevisionRanges(ctx context.Context, group *types.Group) ([]*offline.RevisionRange, error) {
@@ -142,7 +133,7 @@ func (s *OomStore) buildRevisionRanges(ctx context.Context, group *types.Group)
 	return ranges, nil
 }
 
-func GetEntityRowsFromInputFile(ctx context.Context, inputFilePath string) (<-chan types.EntityRow, []string, error) {
+func getEntityRowsFromInputFile(ctx context.Context, inputFilePath string) (<-chan types.EntityRow, []string, error) {
 	input, err := os.Open(inputFilePath)
 	if err != nil {
 		return nil, nil, errdefs.WithStack(err)
@@ -207,34 +198,3 @@ func GetEntityRowsFromInputFile(ctx context.Context, inputFilePath string) (<-ch
 	}()
 	return entityRows, header, nil
 }
-
-func writeJoinResultToFile(outputFilePath string, joinResult *types.JoinResult) error {
-	file, err := os.Create(outputFilePath)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-	w := csv.NewWriter(file)
-	defer w.Flush()
-
-	if err := w.Write(joinResult.Header); err != nil {
-		return err
-	}
-	for row := range joinResult.Data {
-		if row.Error != nil {
-			return row.Error
-		}
-		if err := w.Write(joinRecord(row.Record)); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-func joinRecord(row []interface{}) []string {
-	record := make([]string, 0, len(row))
-	for _, value := range row {
-		record = append(record, cast.ToString(value))
-	}
-	return record
-}
diff --git a/pkg/oomstore/types/options.go b/pkg/oomstore/types/options.go
index 59d0206c9..0492f2b05 100644
--- a/pkg/oomstore/types/options.go
+++ b/pkg/oomstore/types/options.go
@@ -70,9 +70,8 @@ type ChannelJoinOpt struct {
 }
 
 type JoinOpt struct {
-	FeatureNames   []string
-	InputFilePath  string
-	OutputFilePath string
+	FeatureNames  []string
+	InputFilePath string
 }
 
 type UpdateEntityOpt struct {