diff --git a/docs/Configuration.md b/docs/Configuration.md
index 516b23d..e1ac677 100644
--- a/docs/Configuration.md
+++ b/docs/Configuration.md
@@ -123,3 +123,23 @@ Optionally disable syncing to disk per transaction. Nosync being true means much
   * Default: "cayley"
 
 The name of the database within MongoDB to connect to. Manages its own collections and indicies therein.
+
+## Per-Replication Options
+
+The `replication_options` object in the main configuration file contains any of these following options that change the behavior of the replication manager.
+
+### All
+
+#### **`ignore_missing`**
+
+  * Type: Boolean
+  * Default: false
+
+Optionally ignore missing quad on delete.
+
+#### **`ignore_duplicate`**
+
+  * Type: Boolean
+  * Default: false
+
+Optionally ignore duplicated quad on add.
\ No newline at end of file
diff --git a/graph/bolt/quadstore.go b/graph/bolt/quadstore.go
index ed11237..265f948 100644
--- a/graph/bolt/quadstore.go
+++ b/graph/bolt/quadstore.go
@@ -43,6 +43,7 @@ var (
 	}
 	hashSize         = sha1.Size
 	localFillPercent = 0.7
+
 )
 
 type Token struct {
@@ -184,7 +185,7 @@ var (
 	metaBucket = []byte("meta")
 )
 
-func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta) error {
+func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta, ignoreOpts graph.IgnoreOpts) error {
 	oldSize := qs.size
 	oldHorizon := qs.horizon
 	err := qs.db.Update(func(tx *bolt.Tx) error {
@@ -208,6 +209,12 @@ func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta) error {
 		for _, d := range deltas {
 			err := qs.buildQuadWrite(tx, d.Quad, d.ID.Int(), d.Action == graph.Add)
 			if err != nil {
+				if err == graph.ErrQuadExists && ignoreOpts.IgnoreDup{
+					continue
+				}
+				if err == graph.ErrQuadNotExist && ignoreOpts.IgnoreMissing{
+					continue
+				}
 				return err
 			}
 			delta := int64(1)
diff --git a/graph/iterator/mock_ts_test.go b/graph/iterator/mock_ts_test.go
index 2a1407b..6e2b00d 100644
--- a/graph/iterator/mock_ts_test.go
+++ b/graph/iterator/mock_ts_test.go
@@ -35,7 +35,7 @@ func (qs *store) ValueOf(s string) graph.Value {
 	return nil
 }
 
-func (qs *store) ApplyDeltas([]graph.Delta) error { return nil }
+func (qs *store) ApplyDeltas([]graph.Delta, graph.IgnoreOpts) error { return nil }
 
 func (qs *store) Quad(graph.Value) quad.Quad { return quad.Quad{} }
 
diff --git a/graph/leveldb/quadstore.go b/graph/leveldb/quadstore.go
index d6b7611..0a7fe99 100644
--- a/graph/leveldb/quadstore.go
+++ b/graph/leveldb/quadstore.go
@@ -49,6 +49,7 @@ var (
 		New: func() interface{} { return sha1.New() },
 	}
 	hashSize = sha1.Size
+
 )
 
 type Token []byte
@@ -180,7 +181,7 @@ var (
 	cps = [4]quad.Direction{quad.Label, quad.Predicate, quad.Subject, quad.Object}
 )
 
-func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta) error {
+func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta, ignoreOpts graph.IgnoreOpts) error {
 	batch := &leveldb.Batch{}
 	resizeMap := make(map[string]int64)
 	sizeChange := int64(0)
@@ -195,6 +196,12 @@ func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta) error {
 		batch.Put(keyFor(d), bytes)
 		err = qs.buildQuadWrite(batch, d.Quad, d.ID.Int(), d.Action == graph.Add)
 		if err != nil {
+			if err == graph.ErrQuadExists && ignoreOpts.IgnoreDup {
+				continue
+			}
+			if err == graph.ErrQuadNotExist && ignoreOpts.IgnoreMissing {
+				continue
+			}
 			return err
 		}
 		delta := int64(1)
@@ -250,12 +257,17 @@ func (qs *QuadStore) buildQuadWrite(batch *leveldb.Batch, q quad.Quad, id int64,
 	} else {
 		entry.Quad = q
 	}
-	entry.History = append(entry.History, id)
 
-	if isAdd && len(entry.History)%2 == 0 {
-		glog.Error("Entry History is out of sync for", entry)
-		return errors.New("odd index history")
+	if isAdd && len(entry.History)%2 == 1 {
+		glog.Errorf("attempt to add existing quad %v: %#v", entry, q)
+		return graph.ErrQuadExists
 	}
+	if !isAdd && len(entry.History)%2 == 0 {
+		glog.Error("attempt to delete non-existent quad %v: %#c", entry, q)
+		return graph.ErrQuadNotExist
+	}
+
+	entry.History = append(entry.History, id)
 
 	bytes, err := json.Marshal(entry)
 	if err != nil {
diff --git a/graph/memstore/quadstore.go b/graph/memstore/quadstore.go
index 6b11e4e..4a62ec5 100644
--- a/graph/memstore/quadstore.go
+++ b/graph/memstore/quadstore.go
@@ -100,14 +100,20 @@ func newQuadStore() *QuadStore {
 	}
 }
 
-func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta) error {
+func (qs *QuadStore) ApplyDeltas(deltas []graph.Delta, ignoreOpts graph.IgnoreOpts) error {
 	for _, d := range deltas {
 		var err error
 		switch d.Action {
 		case graph.Add:
 			err = qs.AddDelta(d)
+			if err != nil && ignoreOpts.IgnoreDup{
+				err = nil
+			}
 		case graph.Delete:
 			err = qs.RemoveDelta(d)
+			if err != nil && ignoreOpts.IgnoreMissing{
+				err = nil
+			}
 		default:
 			err = errors.New("memstore: invalid action")
 		}
diff --git a/graph/mongo/quadstore.go b/graph/mongo/quadstore.go
index 25c7758..98a5cc3 100644
--- a/graph/mongo/quadstore.go
+++ b/graph/mongo/quadstore.go
@@ -214,7 +214,7 @@ func (qs *QuadStore) updateLog(d graph.Delta) error {
 	return err
 }
 
-func (qs *QuadStore) ApplyDeltas(in []graph.Delta) error {
+func (qs *QuadStore) ApplyDeltas(in []graph.Delta, ignoreOpts graph.IgnoreOpts) error {
 	qs.session.SetSafe(nil)
 	ids := make(map[string]int)
 	// Pre-check the existence condition.
@@ -226,11 +226,19 @@ func (qs *QuadStore) ApplyDeltas(in []graph.Delta) error {
 		switch d.Action {
 		case graph.Add:
 			if qs.checkValid(key) {
-				return graph.ErrQuadExists
+				if ignoreOpts.IgnoreDup {
+					continue
+				}else{
+					return graph.ErrQuadExists
+				}
 			}
 		case graph.Delete:
 			if !qs.checkValid(key) {
-				return graph.ErrQuadNotExist
+				if ignoreOpts.IgnoreMissing {
+					continue
+				}else{
+					return graph.ErrQuadNotExist
+				}
 			}
 		}
 	}
diff --git a/graph/quadstore.go b/graph/quadstore.go
index 79f1df7..cb7eca0 100644
--- a/graph/quadstore.go
+++ b/graph/quadstore.go
@@ -44,7 +44,7 @@ type Value interface{}
 type QuadStore interface {
 	// The only way in is through building a transaction, which
 	// is done by a replication strategy.
-	ApplyDeltas([]Delta) error
+	ApplyDeltas([]Delta, IgnoreOpts) error
 
 	// Given an opaque token, returns the quad for that token from the store.
 	Quad(Value) quad.Quad
diff --git a/graph/quadwriter.go b/graph/quadwriter.go
index 5124d60..fdf65f3 100644
--- a/graph/quadwriter.go
+++ b/graph/quadwriter.go
@@ -24,6 +24,7 @@ package graph
 import (
 	"errors"
 	"time"
+	"flag"
 
 	"github.com/google/cayley/quad"
 )
@@ -48,6 +49,10 @@ type Handle struct {
 	QuadWriter QuadWriter
 }
 
+type IgnoreOpts struct {
+	IgnoreDup, IgnoreMissing bool
+}
+
 func (h *Handle) Close() {
 	h.QuadStore.Close()
 	h.QuadWriter.Close()
@@ -58,6 +63,11 @@ var (
 	ErrQuadNotExist = errors.New("quad does not exist")
 )
 
+var (
+	IgnoreDup = flag.Bool("ignoredup", false, "Don't stop loading on duplicated key on add")
+	IgnoreMissing = flag.Bool("ignoremissing", false, "Don't stop loading on missing key on delete")
+)
+
 type QuadWriter interface {
 	// Add a quad to the store.
 	AddQuad(quad.Quad) error
diff --git a/writer/single.go b/writer/single.go
index d6770a5..4c386b8 100644
--- a/writer/single.go
+++ b/writer/single.go
@@ -26,12 +26,34 @@ func init() {
 }
 
 type Single struct {
-	currentID graph.PrimaryKey
-	qs        graph.QuadStore
+	currentID        graph.PrimaryKey
+	qs               graph.QuadStore
+	ignoreOpts       graph.IgnoreOpts
 }
 
 func NewSingleReplication(qs graph.QuadStore, opts graph.Options) (graph.QuadWriter, error) {
-	return &Single{currentID: qs.Horizon(), qs: qs}, nil
+	var ignoreMissing, ignoreDuplicate bool
+
+	if *graph.IgnoreMissing{
+		ignoreMissing = true
+	}else{
+		ignoreMissing,_ = opts.BoolKey("ignore_missing")
+	}
+
+	if *graph.IgnoreDup{
+		ignoreDuplicate = true
+	}else{
+		ignoreDuplicate,_ = opts.BoolKey("ignore_duplicate")
+	}
+
+	return &Single{
+		currentID: qs.Horizon(), 
+		qs: qs, 
+		ignoreOpts: graph.IgnoreOpts{
+			IgnoreDup: ignoreDuplicate, 
+			IgnoreMissing:ignoreMissing,
+		},
+	}, nil
 }
 
 func (s *Single) AddQuad(q quad.Quad) error {
@@ -42,7 +64,7 @@ func (s *Single) AddQuad(q quad.Quad) error {
 		Action:    graph.Add,
 		Timestamp: time.Now(),
 	}
-	return s.qs.ApplyDeltas(deltas)
+	return s.qs.ApplyDeltas(deltas, s.ignoreOpts)
 }
 
 func (s *Single) AddQuadSet(set []quad.Quad) error {
@@ -55,7 +77,8 @@ func (s *Single) AddQuadSet(set []quad.Quad) error {
 			Timestamp: time.Now(),
 		}
 	}
-	return s.qs.ApplyDeltas(deltas)
+	
+	return s.qs.ApplyDeltas(deltas, s.ignoreOpts)
 }
 
 func (s *Single) RemoveQuad(q quad.Quad) error {
@@ -66,7 +89,7 @@ func (s *Single) RemoveQuad(q quad.Quad) error {
 		Action:    graph.Delete,
 		Timestamp: time.Now(),
 	}
-	return s.qs.ApplyDeltas(deltas)
+	return s.qs.ApplyDeltas(deltas, s.ignoreOpts)
 }
 
 func (s *Single) Close() error {