diff --git a/src/pkg/retention/job.go b/src/pkg/retention/job.go
index f0d88a54af6..db69a8d4589 100644
--- a/src/pkg/retention/job.go
+++ b/src/pkg/retention/job.go
@@ -32,11 +32,11 @@ func (pj *Job) ShouldRetry() bool {
 }
 
 // Validate the parameters
-func (pj *Job) Validate(params Parameters) error {
+func (pj *Job) Validate(params job.Parameters) error {
 	return nil
 }
 
 // Run the job
-func (pj *Job) Run(ctx job.Context, params Parameters) error {
+func (pj *Job) Run(ctx job.Context, params job.Parameters) error {
 	return nil
 }
diff --git a/src/pkg/retention/models.go b/src/pkg/retention/models.go
index c8bcb0a5ab6..958685782ff 100644
--- a/src/pkg/retention/models.go
+++ b/src/pkg/retention/models.go
@@ -16,7 +16,7 @@ package retention
 
 import "time"
 
-// Retention execution
+// Execution of retention
 type Execution struct {
 	ID        string    `json:"id"`
 	PolicyID  string    `json:"policy_id"`
@@ -25,7 +25,7 @@ type Execution struct {
 	Status    string    `json:"status"`
 }
 
-// Retention history
+// History of retention
 type History struct {
 	ExecutionID string `json:"execution_id"`
 	Rule        struct {
diff --git a/src/pkg/retention/periodic_job.go b/src/pkg/retention/periodic_job.go
index f24f5e0d931..bad14af9b2f 100644
--- a/src/pkg/retention/periodic_job.go
+++ b/src/pkg/retention/periodic_job.go
@@ -34,11 +34,11 @@ func (pj *PeriodicJob) ShouldRetry() bool {
 }
 
 // Validate the parameters
-func (pj *PeriodicJob) Validate(params Parameters) error {
+func (pj *PeriodicJob) Validate(params job.Parameters) error {
 	return nil
 }
 
 // Run the job
-func (pj *PeriodicJob) Run(ctx job.Context, params Parameters) error {
+func (pj *PeriodicJob) Run(ctx job.Context, params job.Parameters) error {
 	return ctx.Checkin(fmt.Sprintf("pong=%d", time.Now().Unix()))
 }
diff --git a/src/pkg/retention/policy/action/performer.go b/src/pkg/retention/policy/action/performer.go
index c2ef880719e..da23e14f253 100644
--- a/src/pkg/retention/policy/action/performer.go
+++ b/src/pkg/retention/policy/action/performer.go
@@ -44,7 +44,16 @@ type retainAction struct {
 
 // Perform the action
 func (ra *retainAction) Perform(candidates []*res.Candidate) ([]*res.Result, error) {
-	return nil, nil
+	// TODO: REPLACE SAMPLE CODE WITH REAL IMPLEMENTATION
+	results := make([]*res.Result, 0)
+
+	for _, c := range candidates {
+		results = append(results, &res.Result{
+			Target: c,
+		})
+	}
+
+	return results, nil
 }
 
 // NewRetainAction is factory method for RetainAction
diff --git a/src/pkg/retention/policy/alg/or/processor.go b/src/pkg/retention/policy/alg/or/processor.go
index 120db41b1bf..78ae32b924f 100644
--- a/src/pkg/retention/policy/alg/or/processor.go
+++ b/src/pkg/retention/policy/alg/or/processor.go
@@ -52,7 +52,7 @@ func (p *processor) Process(artifacts []*res.Candidate) ([]*res.Result, error) {
 		// collect errors by wrapping
 		err error
 		// collect processed candidates
-		processedCandidates = make(map[string][]*res.Candidate)
+		processedCandidates = make(map[string]cHash)
 	)
 
 	// for sync
@@ -67,30 +67,36 @@ func (p *processor) Process(artifacts []*res.Candidate) ([]*res.Result, error) {
 	// control chan
 	done := make(chan bool, 1)
 
-	defer func() {
-		// signal the result listener loop exit
-		done <- true
-	}()
-
 	// go routine for receiving results/error
 	go func() {
+		defer func() {
+			// done
+			done <- true
+		}()
+
 		for {
 			select {
 			case result := <-resChan:
+				if result == nil {
+					// chan is closed
+					return
+				}
+
 				if _, ok := processedCandidates[result.action]; !ok {
-					processedCandidates[result.action] = make([]*res.Candidate, 0)
+					processedCandidates[result.action] = make(cHash)
 				}
 
-				processedCandidates[result.action] = append(processedCandidates[result.action], result.processed...)
+				listByAction := processedCandidates[result.action]
+				for _, rp := range result.processed {
+					// remove duplicated ones
+					listByAction[rp.Hash()] = rp
+				}
 			case e := <-errChan:
 				if err == nil {
 					err = errors.Wrap(e, "artifact processing error")
 				} else {
 					err = errors.Wrap(e, err.Error())
 				}
-			case <-done:
-				// exit
-				return
 			}
 		}
 	}()
@@ -143,6 +149,10 @@ func (p *processor) Process(artifacts []*res.Candidate) ([]*res.Result, error) {
 
 	// waiting for all the rules are evaluated
 	wg.Wait()
+	// close result chan
+	close(resChan)
+	// check if the receiving loop exists
+	<-done
 
 	if err != nil {
 		return nil, err
@@ -150,11 +160,13 @@ func (p *processor) Process(artifacts []*res.Candidate) ([]*res.Result, error) {
 
 	results := make([]*res.Result, 0)
 	// Perform actions
-	for act, candidates := range processedCandidates {
+	for act, hash := range processedCandidates {
 		var attachedErr error
 
+		cl := hash.toList()
+
 		if pf, ok := p.performers[act]; ok {
-			if theRes, err := pf.Perform(candidates); err != nil {
+			if theRes, err := pf.Perform(cl); err != nil {
 				attachedErr = err
 			} else {
 				results = append(results, theRes...)
@@ -164,7 +176,7 @@ func (p *processor) Process(artifacts []*res.Candidate) ([]*res.Result, error) {
 		}
 
 		if attachedErr != nil {
-			for _, c := range candidates {
+			for _, c := range cl {
 				results = append(results, &res.Result{
 					Target: c,
 					Error:  attachedErr,
@@ -187,3 +199,15 @@ func (p *processor) AddEvaluator(evaluator rule.Evaluator, selectors []res.Selec
 func (p *processor) AddActionPerformer(action string, performer action.Performer) {
 	p.performers[action] = performer
 }
+
+type cHash map[string]*res.Candidate
+
+func (ch cHash) toList() []*res.Candidate {
+	l := make([]*res.Candidate, 0)
+
+	for _, v := range ch {
+		l = append(l, v)
+	}
+
+	return l
+}
diff --git a/src/pkg/retention/policy/alg/or/processor_test.go b/src/pkg/retention/policy/alg/or/processor_test.go
new file mode 100644
index 00000000000..d4c20c46fa4
--- /dev/null
+++ b/src/pkg/retention/policy/alg/or/processor_test.go
@@ -0,0 +1,103 @@
+// Copyright Project Harbor Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package or
+
+import (
+	"github.com/goharbor/harbor/src/pkg/retention/policy/action"
+	"github.com/goharbor/harbor/src/pkg/retention/policy/alg"
+	"github.com/goharbor/harbor/src/pkg/retention/policy/rule"
+	"github.com/goharbor/harbor/src/pkg/retention/policy/rule/lastx"
+	"github.com/goharbor/harbor/src/pkg/retention/policy/rule/latestk"
+	"github.com/goharbor/harbor/src/pkg/retention/res"
+	"github.com/goharbor/harbor/src/pkg/retention/res/selectors/label"
+	"github.com/goharbor/harbor/src/pkg/retention/res/selectors/regexp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+	"testing"
+	"time"
+)
+
+// ProcessorTestSuite is suite for testing processor
+type ProcessorTestSuite struct {
+	suite.Suite
+
+	p   alg.Processor
+	all []*res.Candidate
+}
+
+// TestProcessor is entrance for ProcessorTestSuite
+func TestProcessor(t *testing.T) {
+	suite.Run(t, new(ProcessorTestSuite))
+}
+
+// SetupSuite ...
+func (suite *ProcessorTestSuite) SetupSuite() {
+	suite.all = []*res.Candidate{
+		{
+			Namespace:  "library",
+			Repository: "harbor",
+			Kind:       "image",
+			Tag:        "latest",
+			PushedTime: time.Now().Unix(),
+			Labels:     []string{"L1", "L2"},
+		},
+		{
+			Namespace:  "library",
+			Repository: "harbor",
+			Kind:       "image",
+			Tag:        "dev",
+			PushedTime: time.Now().Unix(),
+			Labels:     []string{"L3"},
+		},
+	}
+
+	p := New()
+	p.AddActionPerformer(action.Retain, action.NewRetainAction(suite.all))
+
+	lastxParams := make(map[string]rule.Parameter)
+	lastxParams[lastx.ParameterX] = 10
+	p.AddEvaluator(lastx.New(lastxParams), []res.Selector{
+		regexp.New(regexp.Matches, "*dev*"),
+		label.New(label.With, "L1,L2"),
+	})
+
+	latestKParams := make(map[string]rule.Parameter)
+	latestKParams[latestk.ParameterK] = 10
+	p.AddEvaluator(latestk.New(latestKParams), []res.Selector{
+		label.New(label.With, "L3"),
+	})
+
+	suite.p = p
+}
+
+// TearDownSuite ...
+func (suite *ProcessorTestSuite) TearDownSuite() {}
+
+// TestProcess tests process method
+func (suite *ProcessorTestSuite) TestProcess() {
+	results, err := suite.p.Process(suite.all)
+	require.NoError(suite.T(), err)
+	assert.Equal(suite.T(), 2, len(results))
+	assert.Condition(suite.T(), func() bool {
+		for _, r := range results {
+			if r.Error != nil {
+				return false
+			}
+		}
+
+		return true
+	}, "no errors in the returned result list")
+}
diff --git a/src/pkg/retention/policy/rule/evaluator.go b/src/pkg/retention/policy/rule/evaluator.go
index 780d9efa91a..91ec27913df 100644
--- a/src/pkg/retention/policy/rule/evaluator.go
+++ b/src/pkg/retention/policy/rule/evaluator.go
@@ -32,5 +32,5 @@ type Evaluator interface {
 	Action() string
 }
 
-//  RuleFactory defines a factory method for creating rule evaluator
-type RuleFactory func(parameters Parameters) Evaluator
+// Factory defines a factory method for creating rule evaluator
+type Factory func(parameters Parameters) Evaluator
diff --git a/src/pkg/retention/policy/rule/index.go b/src/pkg/retention/policy/rule/index.go
index 3944ef40bf3..cef42176a06 100644
--- a/src/pkg/retention/policy/rule/index.go
+++ b/src/pkg/retention/policy/rule/index.go
@@ -37,7 +37,7 @@ type IndexMeta struct {
 type IndexedParam struct {
 	Name string `json:"name"`
 
-	//Type of the param
+	// Type of the param
 	// "int", "string" or "[]string"
 	Type string `json:"type"`
 
@@ -50,11 +50,11 @@ type IndexedParam struct {
 type indexedItem struct {
 	Meta *IndexMeta
 
-	Factory RuleFactory
+	Factory Factory
 }
 
 // Register the rule evaluator with the corresponding rule template
-func Register(meta *IndexMeta, factory RuleFactory) {
+func Register(meta *IndexMeta, factory Factory) {
 	if meta == nil || factory == nil || len(meta.TemplateID) == 0 {
 		// do nothing
 		return
diff --git a/src/pkg/retention/policy/rule/lastx/evaluator.go b/src/pkg/retention/policy/rule/lastx/evaluator.go
index fc528fcfa8b..284560267b0 100644
--- a/src/pkg/retention/policy/rule/lastx/evaluator.go
+++ b/src/pkg/retention/policy/rule/lastx/evaluator.go
@@ -38,7 +38,8 @@ type evaluator struct {
 
 // Process the candidates based on the rule definition
 func (e *evaluator) Process(artifacts []*res.Candidate) ([]*res.Candidate, error) {
-	return nil, nil
+	// TODO: REPLACE SAMPLE CODE WITH REAL IMPLEMENTATION
+	return artifacts, nil
 }
 
 // Specify what action is performed to the candidates processed by this evaluator
diff --git a/src/pkg/retention/policy/rule/latestk/evaluator.go b/src/pkg/retention/policy/rule/latestk/evaluator.go
index fe23ed5ea8a..a49c5e1cc9b 100644
--- a/src/pkg/retention/policy/rule/latestk/evaluator.go
+++ b/src/pkg/retention/policy/rule/latestk/evaluator.go
@@ -38,7 +38,8 @@ type evaluator struct {
 
 // Process the candidates based on the rule definition
 func (e *evaluator) Process(artifacts []*res.Candidate) ([]*res.Candidate, error) {
-	return nil, nil
+	// TODO: REPLACE SAMPLE CODE WITH REAL IMPLEMENTATION
+	return artifacts, nil
 }
 
 // Specify what action is performed to the candidates processed by this evaluator
diff --git a/src/pkg/retention/res/candidate.go b/src/pkg/retention/res/candidate.go
index 4894854f942..324b696b543 100644
--- a/src/pkg/retention/res/candidate.go
+++ b/src/pkg/retention/res/candidate.go
@@ -14,6 +14,11 @@
 
 package res
 
+import (
+	"encoding/base64"
+	"fmt"
+)
+
 const (
 	// Image kind
 	Image = "image"
@@ -37,3 +42,10 @@ type Candidate struct {
 	// Labels attached with the candidate
 	Labels []string
 }
+
+// Hash code based on the candidate info for differentiation
+func (c *Candidate) Hash() string {
+	raw := fmt.Sprintf("%s:%s/%s:%s", c.Kind, c.Namespace, c.Repository, c.Tag)
+
+	return base64.StdEncoding.EncodeToString([]byte(raw))
+}
diff --git a/src/pkg/retention/res/selectors/label/selector.go b/src/pkg/retention/res/selectors/label/selector.go
index b8b3926edde..efdfdef691a 100644
--- a/src/pkg/retention/res/selectors/label/selector.go
+++ b/src/pkg/retention/res/selectors/label/selector.go
@@ -40,7 +40,8 @@ type selector struct {
 
 // Select candidates by regular expressions
 func (s *selector) Select(artifacts []*res.Candidate) ([]*res.Candidate, error) {
-	return nil, nil
+	// TODO: REPLACE SAMPLE CODE WITH REAL IMPLEMENTATION
+	return artifacts, nil
 }
 
 // New is factory method for list selector
diff --git a/src/pkg/retention/res/selectors/regexp/selector.go b/src/pkg/retention/res/selectors/regexp/selector.go
index 1e320edef6d..0e717c648b1 100644
--- a/src/pkg/retention/res/selectors/regexp/selector.go
+++ b/src/pkg/retention/res/selectors/regexp/selector.go
@@ -39,7 +39,8 @@ type selector struct {
 
 // Select candidates by regular expressions
 func (s *selector) Select(artifacts []*res.Candidate) ([]*res.Candidate, error) {
-	return nil, nil
+	// TODO: REPLACE SAMPLE CODE WITH REAL IMPLEMENTATION
+	return artifacts, nil
 }
 
 // New is factory method for regexp selector