diff --git a/src/mito2/src/memtable/merge_tree.rs b/src/mito2/src/memtable/merge_tree.rs
index a2015c45d327..2a7799524342 100644
--- a/src/mito2/src/memtable/merge_tree.rs
+++ b/src/mito2/src/memtable/merge_tree.rs
@@ -459,4 +459,73 @@ mod tests {
         }
         assert_eq!(expect, v0_all);
     }
+
+    #[test]
+    fn test_write_iter_multi_keys() {
+        write_iter_multi_keys(1, 100);
+        write_iter_multi_keys(2, 100);
+        write_iter_multi_keys(4, 100);
+        write_iter_multi_keys(8, 5);
+        write_iter_multi_keys(2, 10);
+    }
+
+    fn write_iter_multi_keys(max_keys: usize, freeze_threshold: usize) {
+        let metadata = memtable_util::metadata_with_primary_key(vec![1, 0], true);
+        let memtable = MergeTreeMemtable::new(
+            1,
+            metadata.clone(),
+            None,
+            &MergeTreeConfig {
+                index_max_keys_per_shard: max_keys,
+                data_freeze_threshold: freeze_threshold,
+                ..Default::default()
+            },
+        );
+
+        let mut data = Vec::new();
+        // 4 partitions, each partition 4 pks.
+        for i in 0..4 {
+            for j in 0..4 {
+                // key: i, a{j}
+                let timestamps = [11, 13, 1, 5, 3, 7, 9];
+                let key = format!("a{j}");
+                let kvs =
+                    memtable_util::build_key_values(&metadata, key.clone(), i, &timestamps, 0);
+                memtable.write(&kvs).unwrap();
+                for ts in timestamps {
+                    data.push((i, key.clone(), ts));
+                }
+            }
+            for j in 0..4 {
+                // key: i, a{j}
+                let timestamps = [10, 2, 4, 8, 6];
+                let key = format!("a{j}");
+                let kvs =
+                    memtable_util::build_key_values(&metadata, key.clone(), i, &timestamps, 200);
+                memtable.write(&kvs).unwrap();
+                for ts in timestamps {
+                    data.push((i, key.clone(), ts));
+                }
+            }
+        }
+        data.sort_unstable();
+
+        let expect = data.into_iter().map(|x| x.2).collect::<Vec<_>>();
+        let iter = memtable.iter(None, None).unwrap();
+        let read = iter
+            .flat_map(|batch| {
+                batch
+                    .unwrap()
+                    .timestamps()
+                    .as_any()
+                    .downcast_ref::<TimestampMillisecondVector>()
+                    .unwrap()
+                    .iter_data()
+                    .collect::<Vec<_>>()
+                    .into_iter()
+            })
+            .map(|v| v.unwrap().0.value())
+            .collect::<Vec<_>>();
+        assert_eq!(expect, read);
+    }
 }
diff --git a/src/mito2/src/memtable/merge_tree/dict.rs b/src/mito2/src/memtable/merge_tree/dict.rs
index 4be3bac5c3fa..126b8bdb13c8 100644
--- a/src/mito2/src/memtable/merge_tree/dict.rs
+++ b/src/mito2/src/memtable/merge_tree/dict.rs
@@ -108,7 +108,7 @@ impl KeyDictBuilder {
     }
 
     /// Finishes the builder.
-    pub fn finish(&mut self) -> Option<KeyDict> {
+    pub fn finish(&mut self, pk_to_index: &mut BTreeMap<Vec<u8>, PkIndex>) -> Option<KeyDict> {
         if self.key_buffer.is_empty() {
             return None;
         }
@@ -116,11 +116,9 @@ impl KeyDictBuilder {
         // Finishes current dict block and resets the pk index.
         let dict_block = self.key_buffer.finish(true);
         self.dict_blocks.push(dict_block);
-        // Takes the pk to index map.
-        let mut pk_to_index = std::mem::take(&mut self.pk_to_index);
         // Computes key position and then alter pk index.
-        let mut key_positions = vec![0; pk_to_index.len()];
-        for (i, pk_index) in pk_to_index.values_mut().enumerate() {
+        let mut key_positions = vec![0; self.pk_to_index.len()];
+        for (i, pk_index) in self.pk_to_index.values_mut().enumerate() {
             // The position of the i-th key is the old pk index.
             key_positions[i] = *pk_index;
             // Overwrites the pk index.
@@ -129,9 +127,9 @@ impl KeyDictBuilder {
         self.num_keys = 0;
         let key_bytes_in_index = self.key_bytes_in_index;
         self.key_bytes_in_index = 0;
+        *pk_to_index = std::mem::take(&mut self.pk_to_index);
 
         Some(KeyDict {
-            pk_to_index,
             dict_blocks: std::mem::take(&mut self.dict_blocks),
             key_positions,
             key_bytes_in_index,
@@ -214,8 +212,6 @@ fn compute_pk_weights(sorted_pk_indices: &[PkIndex], pk_weights: &mut Vec<u16>)
 #[derive(Default)]
 pub struct KeyDict {
     // TODO(yingwen): We can use key_positions to do a binary search.
-    /// Key map to find a key in the dict.
-    pk_to_index: PkIndexMap,
     /// Unsorted key blocks.
     dict_blocks: Vec<DictBlock>,
     /// Maps pk index to position of the key in [Self::dict_blocks].
@@ -237,11 +233,6 @@ impl KeyDict {
         self.dict_blocks[block_index as usize].key_by_pk_index(position)
     }
 
-    /// Gets the pk index by the key.
-    pub fn get_pk_index(&self, key: &[u8]) -> Option<PkIndex> {
-        self.pk_to_index.get(key).copied()
-    }
-
     /// Returns pk weights to sort a data part and replaces pk indices.
     pub(crate) fn pk_weights_to_sort_data(&self) -> Vec<u16> {
         let mut pk_weights = Vec::with_capacity(self.key_positions.len());
@@ -442,7 +433,7 @@ mod tests {
         assert_eq!(key_bytes, builder.key_bytes_in_index);
         assert_eq!(8850, builder.memory_size());
 
-        let dict = builder.finish().unwrap();
+        let dict = builder.finish(&mut BTreeMap::new()).unwrap();
         assert_eq!(0, builder.key_bytes_in_index);
         assert_eq!(key_bytes, dict.key_bytes_in_index);
         assert!(dict.shared_memory_size() > key_bytes);
@@ -458,7 +449,7 @@ mod tests {
             builder.insert_key(key.as_bytes(), &mut metrics);
         }
         assert!(builder.is_full());
-        builder.finish();
+        builder.finish(&mut BTreeMap::new());
 
         assert!(!builder.is_full());
         assert_eq!(0, builder.insert_key(b"a0", &mut metrics));
diff --git a/src/mito2/src/memtable/merge_tree/partition.rs b/src/mito2/src/memtable/merge_tree/partition.rs
index b147045256c3..e32381c4f5a7 100644
--- a/src/mito2/src/memtable/merge_tree/partition.rs
+++ b/src/mito2/src/memtable/merge_tree/partition.rs
@@ -16,7 +16,7 @@
 //!
 //! We only support partitioning the tree by pre-defined internal columns.
 
-use std::collections::HashSet;
+use std::collections::{HashMap, HashSet};
 use std::sync::{Arc, RwLock};
 
 use api::v1::SemanticType;
@@ -67,17 +67,18 @@ impl Partition {
         metrics: &mut WriteMetrics,
     ) -> Result<()> {
         let mut inner = self.inner.write().unwrap();
-        // Now we ensure one key only exists in one shard.
+        // Freeze the shard builder if needed.
+        if inner.shard_builder.should_freeze() {
+            inner.freeze_active_shard()?;
+        }
+
+        // Finds key in shards, now we ensure one key only exists in one shard.
         if let Some(pk_id) = inner.find_key_in_shards(primary_key) {
             // Key already in shards.
             inner.write_to_shard(pk_id, key_value);
             return Ok(());
         }
 
-        if inner.shard_builder.should_freeze() {
-            inner.freeze_active_shard()?;
-        }
-
         // Write to the shard builder.
         inner
             .shard_builder
@@ -142,19 +143,26 @@ impl Partition {
     ///
     /// Must freeze the partition before fork.
     pub fn fork(&self, metadata: &RegionMetadataRef, config: &MergeTreeConfig) -> Partition {
-        let inner = self.inner.read().unwrap();
-        debug_assert!(inner.shard_builder.is_empty());
-        // TODO(yingwen): TTL or evict shards.
-        let shard_builder = ShardBuilder::new(
-            metadata.clone(),
-            config,
-            inner.shard_builder.current_shard_id(),
-        );
-        let shards = inner
-            .shards
-            .iter()
-            .map(|shard| shard.fork(metadata.clone()))
-            .collect();
+        let (shards, shard_builder) = {
+            let inner = self.inner.read().unwrap();
+            debug_assert!(inner.shard_builder.is_empty());
+            let shard_builder = ShardBuilder::new(
+                metadata.clone(),
+                config,
+                inner.shard_builder.current_shard_id(),
+            );
+            let shards = inner
+                .shards
+                .iter()
+                .map(|shard| shard.fork(metadata.clone()))
+                .collect();
+
+            (shards, shard_builder)
+        };
+        let pk_to_pk_id = {
+            let mut inner = self.inner.write().unwrap();
+            std::mem::take(&mut inner.pk_to_pk_id)
+        };
 
         Partition {
             inner: RwLock::new(Inner {
@@ -162,6 +170,8 @@ impl Partition {
                 shard_builder,
                 shards,
                 num_rows: 0,
+                pk_to_pk_id,
+                frozen: false,
             }),
             dedup: self.dedup,
         }
@@ -461,11 +471,14 @@ fn data_batch_to_batch(
 /// A key only exists in one shard.
 struct Inner {
     metadata: RegionMetadataRef,
+    /// Map to index pk to pk id.
+    pk_to_pk_id: HashMap<Vec<u8>, PkId>,
     /// Shard whose dictionary is active.
     shard_builder: ShardBuilder,
     /// Shards with frozen dictionary.
     shards: Vec<Shard>,
     num_rows: usize,
+    frozen: bool,
 }
 
 impl Inner {
@@ -479,20 +492,17 @@ impl Inner {
         let shard_builder = ShardBuilder::new(metadata.clone(), config, current_shard_id);
         Self {
             metadata,
+            pk_to_pk_id: HashMap::new(),
             shard_builder,
             shards,
             num_rows: 0,
+            frozen: false,
         }
     }
 
     fn find_key_in_shards(&self, primary_key: &[u8]) -> Option<PkId> {
-        for shard in &self.shards {
-            if let Some(pkid) = shard.find_id_by_key(primary_key) {
-                return Some(pkid);
-            }
-        }
-
-        None
+        assert!(!self.frozen);
+        self.pk_to_pk_id.get(primary_key).copied()
     }
 
     fn write_to_shard(&mut self, pk_id: PkId, key_value: KeyValue) {
@@ -506,7 +516,10 @@ impl Inner {
     }
 
     fn freeze_active_shard(&mut self) -> Result<()> {
-        if let Some(shard) = self.shard_builder.finish(self.metadata.clone())? {
+        if let Some(shard) = self
+            .shard_builder
+            .finish(self.metadata.clone(), &mut self.pk_to_pk_id)?
+        {
             self.shards.push(shard);
         }
         Ok(())
diff --git a/src/mito2/src/memtable/merge_tree/shard.rs b/src/mito2/src/memtable/merge_tree/shard.rs
index 9f975d7002f4..9d832e9ada03 100644
--- a/src/mito2/src/memtable/merge_tree/shard.rs
+++ b/src/mito2/src/memtable/merge_tree/shard.rs
@@ -52,17 +52,6 @@ impl Shard {
         }
     }
 
-    /// Returns the pk id of the key if it exists.
-    pub fn find_id_by_key(&self, key: &[u8]) -> Option<PkId> {
-        let key_dict = self.key_dict.as_ref()?;
-        let pk_index = key_dict.get_pk_index(key)?;
-
-        Some(PkId {
-            shard_id: self.shard_id,
-            pk_index,
-        })
-    }
-
     /// Writes a key value into the shard.
     pub fn write_with_pk_id(&mut self, pk_id: PkId, key_value: KeyValue) {
         debug_assert_eq!(self.shard_id, pk_id.shard_id);
@@ -319,43 +308,54 @@ impl Node for ShardNode {
 
 #[cfg(test)]
 mod tests {
+    use std::collections::BTreeMap;
     use std::sync::Arc;
 
     use super::*;
+    use crate::memtable::merge_tree::data::timestamp_array_to_i64_slice;
     use crate::memtable::merge_tree::dict::KeyDictBuilder;
     use crate::memtable::merge_tree::metrics::WriteMetrics;
     use crate::memtable::merge_tree::PkIndex;
     use crate::memtable::KeyValues;
     use crate::test_util::memtable_util::{
-        build_key_values_with_ts_seq_values, encode_key, encode_key_by_kv, encode_keys,
-        metadata_for_test,
+        build_key_values_with_ts_seq_values, encode_keys, metadata_for_test,
     };
 
-    fn input_with_key(metadata: &RegionMetadataRef) -> Vec<KeyValues> {
+    /// Returns key values and expect pk index.
+    fn input_with_key(metadata: &RegionMetadataRef) -> Vec<(KeyValues, PkIndex)> {
         vec![
-            build_key_values_with_ts_seq_values(
-                metadata,
-                "shard".to_string(),
+            (
+                build_key_values_with_ts_seq_values(
+                    metadata,
+                    "shard".to_string(),
+                    2,
+                    [20, 21].into_iter(),
+                    [Some(0.0), Some(1.0)].into_iter(),
+                    0,
+                ),
                 2,
-                [20, 21].into_iter(),
-                [Some(0.0), Some(1.0)].into_iter(),
-                0,
             ),
-            build_key_values_with_ts_seq_values(
-                metadata,
-                "shard".to_string(),
+            (
+                build_key_values_with_ts_seq_values(
+                    metadata,
+                    "shard".to_string(),
+                    0,
+                    [0, 1].into_iter(),
+                    [Some(0.0), Some(1.0)].into_iter(),
+                    1,
+                ),
                 0,
-                [0, 1].into_iter(),
-                [Some(0.0), Some(1.0)].into_iter(),
-                1,
             ),
-            build_key_values_with_ts_seq_values(
-                metadata,
-                "shard".to_string(),
+            (
+                build_key_values_with_ts_seq_values(
+                    metadata,
+                    "shard".to_string(),
+                    1,
+                    [10, 11].into_iter(),
+                    [Some(0.0), Some(1.0)].into_iter(),
+                    2,
+                ),
                 1,
-                [10, 11].into_iter(),
-                [Some(0.0), Some(1.0)].into_iter(),
-                2,
             ),
         ]
     }
@@ -363,55 +363,51 @@ mod tests {
     fn new_shard_with_dict(
         shard_id: ShardId,
         metadata: RegionMetadataRef,
-        input: &[KeyValues],
+        input: &[(KeyValues, PkIndex)],
     ) -> Shard {
         let mut dict_builder = KeyDictBuilder::new(1024);
         let mut metrics = WriteMetrics::default();
         let mut keys = Vec::with_capacity(input.len());
-        for kvs in input {
+        for (kvs, _) in input {
             encode_keys(&metadata, kvs, &mut keys);
         }
         for key in &keys {
             dict_builder.insert_key(key, &mut metrics);
         }
 
-        let dict = dict_builder.finish().unwrap();
+        let dict = dict_builder.finish(&mut BTreeMap::new()).unwrap();
         let data_parts = DataParts::new(metadata, DATA_INIT_CAP, true);
 
         Shard::new(shard_id, Some(Arc::new(dict)), data_parts, true)
     }
 
     #[test]
-    fn test_shard_find_by_key() {
-        let metadata = metadata_for_test();
-        let input = input_with_key(&metadata);
-        let shard = new_shard_with_dict(8, metadata, &input);
-        for i in 0..input.len() {
-            let key = encode_key("shard", i as u32);
-            assert_eq!(
-                PkId {
-                    shard_id: 8,
-                    pk_index: i as PkIndex,
-                },
-                shard.find_id_by_key(&key).unwrap()
-            );
-        }
-        assert!(shard.find_id_by_key(&encode_key("shard", 100)).is_none());
-    }
-
-    #[test]
-    fn test_write_shard() {
+    fn test_write_read_shard() {
         let metadata = metadata_for_test();
         let input = input_with_key(&metadata);
         let mut shard = new_shard_with_dict(8, metadata, &input);
         assert!(shard.is_empty());
-        for key_values in &input {
+        for (key_values, pk_index) in &input {
             for kv in key_values.iter() {
-                let key = encode_key_by_kv(&kv);
-                let pk_id = shard.find_id_by_key(&key).unwrap();
+                let pk_id = PkId {
+                    shard_id: shard.shard_id,
+                    pk_index: *pk_index,
+                };
                 shard.write_with_pk_id(pk_id, kv);
             }
         }
         assert!(!shard.is_empty());
+
+        let mut reader = shard.read().unwrap();
+        let mut timestamps = Vec::new();
+        while reader.is_valid() {
+            let rb = reader.current_data_batch().slice_record_batch();
+            let ts_array = rb.column(1);
+            let ts_slice = timestamp_array_to_i64_slice(ts_array);
+            timestamps.extend_from_slice(ts_slice);
+
+            reader.next().unwrap();
+        }
+        assert_eq!(vec![0, 1, 10, 11, 20, 21], timestamps);
     }
 }
diff --git a/src/mito2/src/memtable/merge_tree/shard_builder.rs b/src/mito2/src/memtable/merge_tree/shard_builder.rs
index c63a1b9f261c..f20a38fe672d 100644
--- a/src/mito2/src/memtable/merge_tree/shard_builder.rs
+++ b/src/mito2/src/memtable/merge_tree/shard_builder.rs
@@ -14,6 +14,7 @@
 
 //! Builder of a shard.
 
+use std::collections::{BTreeMap, HashMap};
 use std::sync::Arc;
 
 use store_api::metadata::RegionMetadataRef;
@@ -78,14 +79,31 @@ impl ShardBuilder {
     /// Builds a new shard and resets the builder.
     ///
     /// Returns `None` if the builder is empty.
-    pub fn finish(&mut self, metadata: RegionMetadataRef) -> Result<Option<Shard>> {
+    pub fn finish(
+        &mut self,
+        metadata: RegionMetadataRef,
+        pk_to_pk_id: &mut HashMap<Vec<u8>, PkId>,
+    ) -> Result<Option<Shard>> {
         if self.is_empty() {
             return Ok(None);
         }
 
-        let key_dict = self.dict_builder.finish();
+        let mut pk_to_index = BTreeMap::new();
+        let key_dict = self.dict_builder.finish(&mut pk_to_index);
         let data_part = match &key_dict {
             Some(dict) => {
+                // Adds mapping to the map.
+                pk_to_pk_id.reserve(pk_to_index.len());
+                for (k, pk_index) in pk_to_index {
+                    pk_to_pk_id.insert(
+                        k,
+                        PkId {
+                            shard_id: self.current_shard_id,
+                            pk_index,
+                        },
+                    );
+                }
+
                 let pk_weights = dict.pk_weights_to_sort_data();
                 self.data_buffer.freeze(Some(&pk_weights), true)?
             }
@@ -162,6 +180,7 @@ impl ShardBuilderReader {
 mod tests {
 
     use super::*;
+    use crate::memtable::merge_tree::data::timestamp_array_to_i64_slice;
     use crate::memtable::merge_tree::metrics::WriteMetrics;
     use crate::memtable::KeyValues;
     use crate::test_util::memtable_util::{
@@ -173,24 +192,24 @@ mod tests {
             build_key_values_with_ts_seq_values(
                 metadata,
                 "shard_builder".to_string(),
-                3,
-                [30, 31].into_iter(),
+                2,
+                [20, 21].into_iter(),
                 [Some(0.0), Some(1.0)].into_iter(),
                 0,
             ),
             build_key_values_with_ts_seq_values(
                 metadata,
                 "shard_builder".to_string(),
-                1,
-                [10, 11].into_iter(),
+                0,
+                [0, 1].into_iter(),
                 [Some(0.0), Some(1.0)].into_iter(),
                 1,
             ),
             build_key_values_with_ts_seq_values(
                 metadata,
                 "shard_builder".to_string(),
-                2,
-                [20, 21].into_iter(),
+                1,
+                [10, 11].into_iter(),
                 [Some(0.0), Some(1.0)].into_iter(),
                 2,
             ),
@@ -204,7 +223,10 @@ mod tests {
         let config = MergeTreeConfig::default();
         let mut shard_builder = ShardBuilder::new(metadata.clone(), &config, 1);
         let mut metrics = WriteMetrics::default();
-        assert!(shard_builder.finish(metadata.clone()).unwrap().is_none());
+        assert!(shard_builder
+            .finish(metadata.clone(), &mut HashMap::new())
+            .unwrap()
+            .is_none());
         assert_eq!(1, shard_builder.current_shard_id);
 
         for key_values in &input {
@@ -213,8 +235,41 @@ mod tests {
                 shard_builder.write_with_key(&key, kv, &mut metrics);
             }
         }
-        let shard = shard_builder.finish(metadata).unwrap().unwrap();
+        let shard = shard_builder
+            .finish(metadata, &mut HashMap::new())
+            .unwrap()
+            .unwrap();
         assert_eq!(1, shard.shard_id);
         assert_eq!(2, shard_builder.current_shard_id);
     }
+
+    #[test]
+    fn test_write_read_shard_builder() {
+        let metadata = metadata_for_test();
+        let input = input_with_key(&metadata);
+        let config = MergeTreeConfig::default();
+        let mut shard_builder = ShardBuilder::new(metadata.clone(), &config, 1);
+        let mut metrics = WriteMetrics::default();
+
+        for key_values in &input {
+            for kv in key_values.iter() {
+                let key = encode_key_by_kv(&kv);
+                shard_builder.write_with_key(&key, kv, &mut metrics);
+            }
+        }
+
+        let mut pk_weights = Vec::new();
+        let mut reader = shard_builder.read(&mut pk_weights).unwrap();
+        let mut timestamps = Vec::new();
+        while reader.is_valid() {
+            let rb = reader.current_data_batch().slice_record_batch();
+            let ts_array = rb.column(1);
+            let ts_slice = timestamp_array_to_i64_slice(ts_array);
+            timestamps.extend_from_slice(ts_slice);
+
+            reader.next().unwrap();
+        }
+        assert_eq!(vec![0, 1, 10, 11, 20, 21], timestamps);
+        assert_eq!(vec![2, 0, 1], pk_weights);
+    }
 }
diff --git a/src/mito2/src/test_util/memtable_util.rs b/src/mito2/src/test_util/memtable_util.rs
index 524b3814866e..002f5d23bd03 100644
--- a/src/mito2/src/test_util/memtable_util.rs
+++ b/src/mito2/src/test_util/memtable_util.rs
@@ -22,7 +22,6 @@ use api::v1::{Row, Rows, SemanticType};
 use datatypes::arrow::array::UInt64Array;
 use datatypes::data_type::ConcreteDataType;
 use datatypes::schema::ColumnSchema;
-use datatypes::value::ValueRef;
 use store_api::metadata::{ColumnMetadata, RegionMetadataBuilder, RegionMetadataRef};
 use store_api::storage::{ColumnId, RegionId, SequenceNumber};
 use table::predicate::Predicate;
@@ -291,16 +290,6 @@ pub(crate) fn encode_keys(
     }
 }
 
-/// Encode one key.
-pub(crate) fn encode_key(k0: &str, k1: u32) -> Vec<u8> {
-    let row_codec = McmpRowCodec::new(vec![
-        SortField::new(ConcreteDataType::string_datatype()),
-        SortField::new(ConcreteDataType::uint32_datatype()),
-    ]);
-    let key = [ValueRef::String(k0), ValueRef::UInt32(k1)];
-    row_codec.encode(key.into_iter()).unwrap()
-}
-
 /// Encode one key.
 pub(crate) fn encode_key_by_kv(key_value: &KeyValue) -> Vec<u8> {
     let row_codec = McmpRowCodec::new(vec![