diff --git a/.vscode/settings.json b/.vscode/settings.json
index 24c094cc..55afda20 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -10,6 +10,7 @@
     "LOGSTORE",
     "napi",
     "nextest",
+    "peekable",
     "Peritext",
     "RUSTFLAGS",
     "smstring",
diff --git a/crates/loro-internal/src/container/list/list_container.rs b/crates/loro-internal/src/container/list/list_container.rs
index 386dd5b5..fb6a54c6 100644
--- a/crates/loro-internal/src/container/list/list_container.rs
+++ b/crates/loro-internal/src/container/list/list_container.rs
@@ -473,10 +473,8 @@ impl Container for ListContainer {
             InnerContent::List(op) => match op {
                 InnerListOp::Insert { slice, pos } => {
                     if should_notify {
-                        let mut delta = Delta::new();
                         let delta_vec = self.raw_data.slice(&slice.0).to_vec();
-                        delta.retain(*pos);
-                        delta.insert(delta_vec);
+                        let delta = Delta::new().retain(*pos).insert(delta_vec);
                         context.push_diff(&self.id, Diff::List(delta));
                     }
 
@@ -485,9 +483,9 @@ impl Container for ListContainer {
                 }
                 InnerListOp::Delete(span) => {
                     if should_notify {
-                        let mut delta = Delta::new();
-                        delta.retain(span.start() as usize);
-                        delta.delete(span.atom_len());
+                        let delta = Delta::new()
+                            .retain(span.start() as usize)
+                            .delete(span.atom_len());
                         context.push_diff(&self.id, Diff::List(delta));
                     }
 
@@ -543,9 +541,7 @@ impl Container for ListContainer {
             match effect {
                 Effect::Del { pos, len } => {
                     if should_notify {
-                        let mut delta = Delta::new();
-                        delta.retain(pos);
-                        delta.delete(len);
+                        let delta = Delta::new().retain(pos).delete(len);
                         diff.push(Diff::List(delta));
                     }
 
@@ -568,15 +564,12 @@ impl Container for ListContainer {
                 }
                 Effect::Ins { pos, content } => {
                     if should_notify {
-                        let mut delta = Delta::new();
-                        delta.retain(pos);
                         let s = if content.is_unknown() {
                             (0..content.atom_len()).map(|_| LoroValue::Null).collect()
                         } else {
                             self.raw_data.slice(&content.0).to_vec()
                         };
-
-                        delta.insert(s);
+                        let delta = Delta::new().retain(pos).insert(s);
                         diff.push(Diff::List(delta));
                     }
                     if !content.is_unknown() {
@@ -665,10 +658,9 @@ impl Container for ListContainer {
             // notify
             let should_notify = hierarchy.should_notify(&self.id);
             if should_notify {
-                let mut delta = Delta::new();
                 let delta_vec = self.raw_data.slice(&(0..state_len)).to_vec();
-                delta.retain(0);
-                delta.insert(delta_vec);
+                let delta = Delta::new().retain(0).insert(delta_vec);
+
                 ctx.push_diff(&self.id, Diff::List(delta));
             }
         } else {
@@ -850,9 +842,9 @@ mod test {
         let mut loro = LoroCore::default();
         let mut list = loro.get_list("id");
         {
-            let mut txn = loro.transact();
-            list.insert(&mut txn, 0, 123).unwrap();
-            list.insert(&mut txn, 1, 123).unwrap();
+            let txn = loro.transact();
+            list.insert(&txn, 0, 123).unwrap();
+            list.insert(&txn, 1, 123).unwrap();
         }
         assert_eq!(list.get(0), Some(123.into()));
         assert_eq!(list.get(1), Some(123.into()));
diff --git a/crates/loro-internal/src/container/text/text_container.rs b/crates/loro-internal/src/container/text/text_container.rs
index d4b36d5f..5d16b525 100644
--- a/crates/loro-internal/src/container/text/text_container.rs
+++ b/crates/loro-internal/src/container/text/text_container.rs
@@ -367,9 +367,7 @@ impl Container for TextContainer {
                         } else {
                             self.raw_str.slice(&slice.0).to_owned()
                         };
-                        let mut delta = Delta::new();
-                        delta.retain(*pos);
-                        delta.insert(s);
+                        let delta = Delta::new().retain(*pos).insert(s);
                         ctx.push_diff(&self.id, Diff::Text(delta));
                     }
                     self.state.insert(
@@ -379,9 +377,9 @@ impl Container for TextContainer {
                 }
                 InnerListOp::Delete(span) => {
                     if should_notify {
-                        let mut delta = Delta::new();
-                        delta.retain(span.start() as usize);
-                        delta.delete(span.atom_len());
+                        let delta = Delta::new()
+                            .retain(span.start() as usize)
+                            .delete(span.atom_len());
                         ctx.push_diff(&self.id, Diff::Text(delta));
                     }
 
@@ -433,9 +431,7 @@ impl Container for TextContainer {
             match effect {
                 Effect::Del { pos, len } => {
                     if should_notify {
-                        let mut delta = Delta::new();
-                        delta.retain(pos);
-                        delta.delete(len);
+                        let delta = Delta::new().retain(pos).delete(len);
                         diff.push(Diff::Text(delta));
                     }
 
@@ -449,9 +445,7 @@ impl Container for TextContainer {
                         } else {
                             self.raw_str.slice(&content.0).to_owned()
                         };
-                        let mut delta = Delta::new();
-                        delta.retain(pos);
-                        delta.insert(s);
+                        let delta = Delta::new().retain(pos).insert(s);
                         diff.push(Diff::Text(delta));
                     }
 
@@ -544,9 +538,7 @@ impl Container for TextContainer {
             let should_notify = hierarchy.should_notify(&self.id);
             if should_notify {
                 let s = self.raw_str.slice(&(0..state_len)).to_owned();
-                let mut delta = Delta::new();
-                delta.retain(0);
-                delta.insert(s);
+                let delta = Delta::new().retain(0).insert(s);
                 ctx.push_diff(&self.id, Diff::Text(delta));
             }
         } else {
diff --git a/crates/loro-internal/src/delta.rs b/crates/loro-internal/src/delta.rs
index a2df548a..9acc48b6 100644
--- a/crates/loro-internal/src/delta.rs
+++ b/crates/loro-internal/src/delta.rs
@@ -1,10 +1,14 @@
 use enum_as_inner::EnumAsInner;
-use rle::{HasLength, Mergable, RleVec};
+use rle::{HasLength, Mergable, RleVec, Sliceable};
 use serde::Serialize;
+use smallvec::{smallvec, IntoIter, SmallVec};
+use std::fmt::Debug;
+
+use crate::LoroValue;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Delta<Value, Meta = ()> {
-    vec: RleVec<[DeltaItem<Value, Meta>; 1]>,
+    vec: SmallVec<[DeltaItem<Value, Meta>; 2]>,
 }
 
 impl<V: Serialize, M: Serialize> Serialize for Delta<V, M> {
@@ -23,6 +27,42 @@ pub enum DeltaItem<Value, Meta> {
     Delete(usize),
 }
 
+pub trait Meta: Debug + Default + Clone + PartialEq {
+    fn is_empty(&self) -> bool;
+}
+
+impl Meta for () {
+    fn is_empty(&self) -> bool {
+        true
+    }
+}
+
+pub trait DeltaValue: Debug + HasLength + Sliceable + Clone + PartialEq {
+    fn merge(&mut self, other: Self);
+}
+
+impl<Value: DeltaValue, M: Meta> DeltaItem<Value, M> {
+    pub fn meta(&self) -> Option<&M> {
+        match self {
+            DeltaItem::Insert { value, meta } => Some(meta),
+            DeltaItem::Retain { len, meta } => Some(meta),
+            _ => None,
+        }
+    }
+
+    pub fn is_retain(&self) -> bool {
+        matches!(self, Self::Retain { .. })
+    }
+
+    pub fn is_insert(&self) -> bool {
+        matches!(self, Self::Insert { .. })
+    }
+
+    pub fn is_delete(&self) -> bool {
+        matches!(self, Self::Delete(_))
+    }
+}
+
 impl<Value: HasLength, Meta> HasLength for DeltaItem<Value, Meta> {
     fn content_len(&self) -> usize {
         match self {
@@ -35,31 +75,220 @@ impl<Value: HasLength, Meta> HasLength for DeltaItem<Value, Meta> {
 
 impl<Value, Meta> Mergable for DeltaItem<Value, Meta> {}
 
-impl<Value: HasLength, Meta> Delta<Value, Meta> {
+pub struct DeltaIterator<V, M: Meta> {
+    ops: SmallVec<[DeltaItem<V, M>; 2]>,
+    index: usize,
+    offset: usize,
+}
+
+impl<V: DeltaValue, M: Meta> DeltaIterator<V, M> {
+    fn new(ops: SmallVec<[DeltaItem<V, M>; 2]>) -> Self {
+        Self {
+            ops,
+            index: 0,
+            offset: 0,
+        }
+    }
+
+    fn next<L: Into<Option<usize>>>(&mut self, len: L) -> DeltaItem<V, M> {
+        self.next_impl(len.into())
+    }
+
+    fn next_impl(&mut self, mut len: Option<usize>) -> DeltaItem<V, M> {
+        if len.is_none() {
+            len = Some(usize::MAX)
+        }
+        let mut length = len.unwrap();
+        {
+            let next_op = self.peek();
+            if next_op.is_none() {
+                return DeltaItem::Retain {
+                    len: usize::MAX,
+                    meta: Default::default(),
+                };
+            }
+        }
+        // TODO: Maybe can avoid cloning
+        let op = self.peek().unwrap().clone();
+        let op_length = op.content_len();
+        let offset = self.offset;
+        if length >= op_length - offset {
+            length = op_length - offset;
+            self.index += 1;
+            self.offset = 0;
+        } else {
+            self.offset += length;
+        }
+
+        if op.is_delete() {
+            DeltaItem::Delete(length)
+        } else {
+            let mut ans_op = op;
+            if ans_op.is_retain() {
+                *ans_op.as_retain_mut().unwrap().0 = length;
+            } else if ans_op.is_insert() {
+                let v = ans_op.as_insert_mut().unwrap().0;
+                *v = v.slice(offset, offset + length);
+            }
+            ans_op
+        }
+    }
+
+    fn rest(&mut self) -> SmallVec<[DeltaItem<V, M>; 2]> {
+        if !self.has_next() {
+            smallvec![]
+        } else if self.offset == 0 {
+            // TODO avoid cloning
+            self.ops[self.index..].into()
+        } else {
+            let offset = self.offset;
+            let index = self.index;
+            let next = self.next(None);
+            let rest = self.ops[self.index..].to_vec();
+            self.offset = offset;
+            self.index = index;
+            let mut ans = smallvec![next];
+            ans.extend(rest);
+            ans
+        }
+    }
+
+    fn has_next(&self) -> bool {
+        self.peek_length() < usize::MAX
+    }
+
+    fn peek(&self) -> Option<&DeltaItem<V, M>> {
+        self.ops.get(self.index)
+    }
+
+    fn peek_length(&self) -> usize {
+        if let Some(op) = self.peek() {
+            if op.content_len() == usize::MAX {
+                return usize::MAX;
+            }
+            op.content_len() - self.offset
+        } else {
+            usize::MAX
+        }
+    }
+
+    // fn peek_is_retain(&self) -> bool {
+    //     if let Some(op) = self.peek() {
+    //         op.is_retain()
+    //     } else {
+    //         // default
+    //         true
+    //     }
+    // }
+
+    fn peek_is_insert(&self) -> bool {
+        if let Some(op) = self.peek() {
+            op.is_insert()
+        } else {
+            false
+        }
+    }
+
+    fn peek_is_delete(&self) -> bool {
+        if let Some(op) = self.peek() {
+            op.is_delete()
+        } else {
+            false
+        }
+    }
+}
+
+impl<Value: DeltaValue, M: Meta> Delta<Value, M> {
     pub fn new() -> Self {
-        Self { vec: RleVec::new() }
+        Self {
+            vec: SmallVec::new(),
+        }
     }
 
-    pub fn retain_with_meta(&mut self, len: usize, meta: Meta) {
+    pub fn retain_with_meta(mut self, len: usize, meta: M) -> Self {
         self.vec.push(DeltaItem::Retain { len, meta });
+        self
     }
 
-    pub fn insert_with_meta(&mut self, value: Value, meta: Meta) {
+    pub fn insert_with_meta(mut self, value: Value, meta: M) -> Self {
         self.vec.push(DeltaItem::Insert { value, meta });
+        self
     }
 
-    pub fn delete(&mut self, len: usize) {
+    pub fn delete(mut self, len: usize) -> Self {
+        if len == 0 {
+            return self;
+        }
         self.vec.push(DeltaItem::Delete(len));
+        self
     }
 
-    pub fn iter(&self) -> impl Iterator<Item = &DeltaItem<Value, Meta>> {
+    pub fn push(&mut self, new_op: DeltaItem<Value, M>) {
+        let mut index = self.vec.len();
+        let last_op = self.vec.last_mut();
+        if let Some(mut last_op) = last_op {
+            if new_op.is_delete() && last_op.is_delete() {
+                self.vec[index - 1] =
+                    DeltaItem::Delete(last_op.content_len() + new_op.content_len());
+                return;
+            }
+            // Since it does not matter if we insert before or after deleting at the same index,
+            // always prefer to insert first
+            if last_op.is_delete() && new_op.is_insert() {
+                index -= 1;
+                let _last_op = self.vec.get_mut(index - 1);
+                if let Some(_last_op_inner) = _last_op {
+                    last_op = _last_op_inner;
+                } else {
+                    self.vec.insert(0, new_op);
+                    return;
+                }
+            }
+            if new_op.meta() == last_op.meta() {
+                if new_op.is_insert() && last_op.is_insert() {
+                    // TODO avoid cloning
+                    let mut value = last_op.as_insert_mut().unwrap().0.clone();
+                    value.merge(new_op.as_insert().unwrap().0.clone());
+                    self.vec[index - 1] = DeltaItem::Insert {
+                        value,
+                        meta: new_op.meta().unwrap().clone(),
+                    };
+                    return;
+                } else if new_op.is_retain() && last_op.is_retain() {
+                    println!("last op {:?} new_op {:?}", last_op, new_op);
+                    println!(
+                        "len = {} + {}  usize MAX {}",
+                        last_op.content_len(),
+                        new_op.content_len(),
+                        usize::MAX
+                    );
+                    self.vec[index - 1] = DeltaItem::Retain {
+                        len: last_op.content_len() + new_op.content_len(),
+                        meta: new_op.meta().unwrap().clone(),
+                    };
+                    return;
+                }
+            }
+        }
+        if index == self.vec.len() {
+            self.vec.push(new_op);
+        } else {
+            self.vec.insert(index, new_op);
+        }
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = &DeltaItem<Value, M>> {
         self.vec.iter()
     }
 
-    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut DeltaItem<Value, Meta>> {
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut DeltaItem<Value, M>> {
         self.vec.iter_mut()
     }
 
+    pub fn into_op_iter(self) -> DeltaIterator<Value, M> {
+        DeltaIterator::new(self.vec)
+    }
+
     pub fn len(&self) -> usize {
         self.vec.len()
     }
@@ -67,30 +296,160 @@ impl<Value: HasLength, Meta> Delta<Value, Meta> {
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }
+
+    /// Reference: [Quill Delta](https://github.com/quilljs/delta)
+    pub fn compose(self, other: Self) -> Self {
+        let mut this_iter = self.into_op_iter();
+        let mut other_iter = other.into_op_iter();
+        let mut ops = vec![];
+        let first_other = other_iter.peek();
+        if let Some(first_other) = first_other {
+            if first_other.is_retain()
+                && (first_other.meta().is_none() || first_other.meta().unwrap().is_empty())
+            {
+                let mut first_left = first_other.content_len();
+                let mut first_this = this_iter.peek();
+                while let Some(first_this_inner) = first_this {
+                    if first_this_inner.is_insert() && first_this_inner.content_len() <= first_left
+                    {
+                        first_left -= first_this_inner.content_len();
+                        ops.push(this_iter.next(None));
+                        first_this = this_iter.peek();
+                    } else {
+                        break;
+                    }
+                }
+                if first_other.content_len() - first_left > 0 {
+                    other_iter.next(first_other.content_len() - first_left);
+                }
+            }
+        }
+        let mut delta = Delta::new();
+        while this_iter.has_next() || other_iter.has_next() {
+            if other_iter.peek_is_insert() {
+                delta.push(other_iter.next(None));
+            } else if this_iter.peek_is_delete() {
+                delta.push(this_iter.next(None));
+            } else {
+                let length = this_iter.peek_length().min(other_iter.peek_length());
+                let this_op = this_iter.next(length);
+                let other_op = other_iter.next(length);
+                if other_op.is_retain() {
+                    let new_op = if this_op.is_retain() {
+                        DeltaItem::Retain {
+                            len: length,
+                            meta: M::default(),
+                        }
+                    } else {
+                        this_op.clone()
+                    };
+                    // TODO: Meta compose
+                    delta.push(new_op.clone());
+                    if !other_iter.has_next() && delta.vec[delta.vec.len() - 1].eq(&new_op) {
+                        let rest = Delta {
+                            vec: this_iter.rest(),
+                        };
+                        return delta.concat(rest).chop();
+                    }
+                } else if other_op.is_delete() {
+                    if this_op.is_retain() {
+                        delta.push(other_op);
+                    } else {
+                        // this op is insert
+                        continue;
+                    }
+                }
+            }
+        }
+        delta.chop()
+    }
+
+    fn concat(&mut self, mut other: Self) -> Self {
+        let mut delta = Delta {
+            vec: self.vec.clone(),
+        };
+        if !other.vec.is_empty() {
+            // TODO: why?
+            let other_first = other.vec.remove(0);
+            delta.push(other_first);
+            delta.vec.extend(other.vec);
+        }
+        delta
+    }
+
+    fn chop(mut self) -> Self {
+        let last_op = self.vec.last();
+        if let Some(last_op) = last_op {
+            // TODO: check
+            if last_op.is_retain() && last_op.meta().unwrap().is_empty() {
+                self.vec.pop();
+            }
+        }
+        self
+    }
 }
 
-impl<Value: HasLength, Meta> Default for Delta<Value, Meta> {
+impl<Value: DeltaValue, M: Meta> Default for Delta<Value, M> {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl<Value: HasLength, Meta: Default> Delta<Value, Meta> {
-    pub fn retain(&mut self, len: usize) {
+impl<Value: HasLength, M: Default + Meta> Delta<Value, M> {
+    pub fn retain(mut self, len: usize) -> Self {
         if len == 0 {
-            return;
+            return self;
         }
 
         self.vec.push(DeltaItem::Retain {
             len,
             meta: Default::default(),
         });
+        self
     }
 
-    pub fn insert(&mut self, value: Value) {
+    pub fn insert(mut self, value: Value) -> Self {
         self.vec.push(DeltaItem::Insert {
             value,
             meta: Default::default(),
         });
+        self
+    }
+}
+
+impl DeltaValue for Vec<LoroValue> {
+    fn merge(&mut self, other: Self) {
+        self.extend(other)
+    }
+}
+
+impl DeltaValue for String {
+    fn merge(&mut self, other: Self) {
+        self.push_str(&other)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::{Delta, DeltaItem};
+
+    #[test]
+    fn delta_push() {
+        let mut a: Delta<String, ()> = Delta::new().insert("a".to_string());
+        a.push(DeltaItem::Insert {
+            value: "b".to_string(),
+            meta: (),
+        });
+        assert_eq!(a, Delta::new().insert("ab".to_string()));
+    }
+
+    #[test]
+    fn delta_compose() {
+        let a: Delta<String, ()> = Delta::new().retain(3).insert("abcde".to_string());
+        let b = Delta::new().retain(5).delete(6);
+        assert_eq!(
+            a.compose(b),
+            Delta::new().retain(3).insert("ab".to_string()).delete(3)
+        );
     }
 }
diff --git a/crates/loro-internal/src/transaction.rs b/crates/loro-internal/src/transaction.rs
index ca27379d..bcb13edd 100644
--- a/crates/loro-internal/src/transaction.rs
+++ b/crates/loro-internal/src/transaction.rs
@@ -57,7 +57,7 @@ impl Deref for TransactionWrap {
     }
 }
 
-pub struct TransactionWrap(pub Arc<Mutex<Transaction>>);
+pub struct TransactionWrap(pub(crate) Arc<Mutex<Transaction>>);
 
 pub struct Transaction {
     client_id: ClientID,
diff --git a/crates/loro-internal/src/transaction/op.rs b/crates/loro-internal/src/transaction/op.rs
index 65deda7d..f2513897 100644
--- a/crates/loro-internal/src/transaction/op.rs
+++ b/crates/loro-internal/src/transaction/op.rs
@@ -67,6 +67,7 @@ pub enum ListTxnOp {
     Delete {
         pos: usize,
         len: usize,
+        
         deleted_container: Option<SmallVec<[ContainerIdx; 1]>>,
     },
 }
diff --git a/crates/rle/src/rle_trait.rs b/crates/rle/src/rle_trait.rs
index b2b475e2..a1fc782b 100644
--- a/crates/rle/src/rle_trait.rs
+++ b/crates/rle/src/rle_trait.rs
@@ -96,3 +96,15 @@ impl<T> HasLength for Vec<T> {
         self.len()
     }
 }
+
+impl<T: Clone> Sliceable for Vec<T> {
+    fn slice(&self, from: usize, to: usize) -> Self {
+        self[from..to].to_vec()
+    }
+}
+
+impl Sliceable for String {
+    fn slice(&self, from: usize, to: usize) -> Self {
+        self[from..to].to_string()
+    }
+}
diff --git a/crates/rle/src/rle_vec_old.rs b/crates/rle/src/rle_vec_old.rs
index 090c8254..1105c253 100644
--- a/crates/rle/src/rle_vec_old.rs
+++ b/crates/rle/src/rle_vec_old.rs
@@ -357,12 +357,6 @@ mod test {
             }
         }
 
-        impl Sliceable for String {
-            fn slice(&self, start: usize, end: usize) -> Self {
-                self[start..end].to_string()
-            }
-        }
-
         #[test]
         fn get_at_atom_index() {
             let mut vec: RleVecWithIndex<String> = RleVecWithIndex::new();