diff --git a/src/lib.rs b/src/lib.rs
index 60dc2956..a2acf57b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -94,6 +94,8 @@
 
 pub mod backoff;
 #[doc(hidden)]
+pub mod proto; // export `proto` to enable user customized codec
+#[doc(hidden)]
 pub mod raw;
 pub mod request;
 #[doc(hidden)]
@@ -104,7 +106,6 @@ mod compat;
 mod config;
 mod kv;
 mod pd;
-mod proto;
 mod region;
 mod region_cache;
 mod stats;
@@ -145,6 +146,8 @@ pub use crate::raw::Client as RawClient;
 #[doc(inline)]
 pub use crate::raw::ColumnFamily;
 #[doc(inline)]
+pub use crate::request::codec;
+#[doc(inline)]
 pub use crate::request::RetryOptions;
 #[doc(inline)]
 pub use crate::timestamp::Timestamp;
diff --git a/src/mock.rs b/src/mock.rs
index eada6a8e..3b0b157f 100644
--- a/src/mock.rs
+++ b/src/mock.rs
@@ -18,6 +18,7 @@ use crate::proto::metapb::RegionEpoch;
 use crate::proto::metapb::{self};
 use crate::region::RegionId;
 use crate::region::RegionWithLeader;
+use crate::request::codec::ApiV1TxnCodec;
 use crate::store::KvClient;
 use crate::store::KvConnect;
 use crate::store::RegionStore;
@@ -30,7 +31,7 @@ use crate::Timestamp;
 
 /// Create a `PdRpcClient` with it's internals replaced with mocks so that the
 /// client can be tested without doing any RPC calls.
-pub async fn pd_rpc_client() -> PdRpcClient<MockKvConnect, MockCluster> {
+pub async fn pd_rpc_client() -> PdRpcClient<ApiV1TxnCodec, MockKvConnect, MockCluster> {
     let config = Config::default();
     PdRpcClient::new(
         config.clone(),
@@ -43,6 +44,7 @@ pub async fn pd_rpc_client() -> PdRpcClient<MockKvConnect, MockCluster> {
             ))
         },
         false,
+        Some(ApiV1TxnCodec::default()),
     )
     .await
     .unwrap()
@@ -71,9 +73,18 @@ pub struct MockKvConnect;
 
 pub struct MockCluster;
 
-#[derive(new)]
 pub struct MockPdClient {
     client: MockKvClient,
+    codec: ApiV1TxnCodec,
+}
+
+impl MockPdClient {
+    pub fn new(client: MockKvClient) -> MockPdClient {
+        MockPdClient {
+            client,
+            codec: ApiV1TxnCodec::default(),
+        }
+    }
 }
 
 #[async_trait]
@@ -102,6 +113,7 @@ impl MockPdClient {
     pub fn default() -> MockPdClient {
         MockPdClient {
             client: MockKvClient::default(),
+            codec: ApiV1TxnCodec::default(),
         }
     }
 
@@ -165,6 +177,7 @@ impl MockPdClient {
 
 #[async_trait]
 impl PdClient for MockPdClient {
+    type Codec = ApiV1TxnCodec;
     type KvClient = MockKvClient;
 
     async fn map_region_to_store(self: Arc<Self>, region: RegionWithLeader) -> Result<RegionStore> {
@@ -210,4 +223,8 @@ impl PdClient for MockPdClient {
     }
 
     async fn invalidate_region_cache(&self, _ver_id: crate::region::RegionVerId) {}
+
+    fn get_codec(&self) -> &Self::Codec {
+        &self.codec
+    }
 }
diff --git a/src/pd/client.rs b/src/pd/client.rs
index 31f88968..f291c62c 100644
--- a/src/pd/client.rs
+++ b/src/pd/client.rs
@@ -20,6 +20,7 @@ use crate::region::RegionId;
 use crate::region::RegionVerId;
 use crate::region::RegionWithLeader;
 use crate::region_cache::RegionCache;
+use crate::request::codec::{ApiV1TxnCodec, Codec};
 use crate::store::KvClient;
 use crate::store::KvConnect;
 use crate::store::RegionStore;
@@ -50,6 +51,7 @@ use crate::Timestamp;
 /// So if we use transactional APIs, keys in PD are encoded and PD does not know about the encoding stuff.
 #[async_trait]
 pub trait PdClient: Send + Sync + 'static {
+    type Codec: Codec;
     type KvClient: KvClient + Send + Sync + 'static;
 
     /// In transactional API, `region` is decoded (keys in raw format).
@@ -189,8 +191,11 @@ pub trait PdClient: Send + Sync + 'static {
         .boxed()
     }
 
-    fn decode_region(mut region: RegionWithLeader, enable_codec: bool) -> Result<RegionWithLeader> {
-        if enable_codec {
+    fn decode_region(
+        mut region: RegionWithLeader,
+        enable_mvcc_codec: bool,
+    ) -> Result<RegionWithLeader> {
+        if enable_mvcc_codec {
             codec::decode_bytes_in_place(&mut region.region.start_key, false)?;
             codec::decode_bytes_in_place(&mut region.region.end_key, false)?;
         }
@@ -200,20 +205,30 @@ pub trait PdClient: Send + Sync + 'static {
     async fn update_leader(&self, ver_id: RegionVerId, leader: metapb::Peer) -> Result<()>;
 
     async fn invalidate_region_cache(&self, ver_id: RegionVerId);
+
+    /// Get the codec carried by `PdClient`.
+    /// The purpose of carrying the codec is to avoid passing it on so many calling paths.
+    fn get_codec(&self) -> &Self::Codec;
 }
 
 /// This client converts requests for the logical TiKV cluster into requests
 /// for a single TiKV store using PD and internal logic.
-pub struct PdRpcClient<KvC: KvConnect + Send + Sync + 'static = TikvConnect, Cl = Cluster> {
+pub struct PdRpcClient<
+    Cod: Codec = ApiV1TxnCodec,
+    KvC: KvConnect + Send + Sync + 'static = TikvConnect,
+    Cl = Cluster,
+> {
     pd: Arc<RetryClient<Cl>>,
     kv_connect: KvC,
     kv_client_cache: Arc<RwLock<HashMap<String, KvC::KvClient>>>,
-    enable_codec: bool,
+    enable_mvcc_codec: bool,
     region_cache: RegionCache<RetryClient<Cl>>,
+    codec: Option<Cod>,
 }
 
 #[async_trait]
-impl<KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<KvC> {
+impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<Cod, KvC> {
+    type Codec = Cod;
     type KvClient = KvC::KvClient;
 
     async fn map_region_to_store(self: Arc<Self>, region: RegionWithLeader) -> Result<RegionStore> {
@@ -224,20 +239,20 @@ impl<KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<KvC> {
     }
 
     async fn region_for_key(&self, key: &Key) -> Result<RegionWithLeader> {
-        let enable_codec = self.enable_codec;
-        let key = if enable_codec {
+        let enable_mvcc_codec = self.enable_mvcc_codec;
+        let key = if enable_mvcc_codec {
             key.to_encoded()
         } else {
             key.clone()
         };
 
         let region = self.region_cache.get_region_by_key(&key).await?;
-        Self::decode_region(region, enable_codec)
+        Self::decode_region(region, enable_mvcc_codec)
     }
 
     async fn region_for_id(&self, id: RegionId) -> Result<RegionWithLeader> {
         let region = self.region_cache.get_region_by_id(id).await?;
-        Self::decode_region(region, self.enable_codec)
+        Self::decode_region(region, self.enable_mvcc_codec)
     }
 
     async fn get_timestamp(self: Arc<Self>) -> Result<Timestamp> {
@@ -255,31 +270,40 @@ impl<KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<KvC> {
     async fn invalidate_region_cache(&self, ver_id: RegionVerId) {
         self.region_cache.invalidate_region_cache(ver_id).await
     }
+
+    fn get_codec(&self) -> &Self::Codec {
+        self.codec
+            .as_ref()
+            .unwrap_or_else(|| panic!("codec not set"))
+    }
 }
 
-impl PdRpcClient<TikvConnect, Cluster> {
+impl<Cod: Codec> PdRpcClient<Cod, TikvConnect, Cluster> {
     pub async fn connect(
         pd_endpoints: &[String],
         config: Config,
-        enable_codec: bool,
-    ) -> Result<PdRpcClient> {
+        enable_mvcc_codec: bool, // TODO: infer from `codec`.
+        codec: Option<Cod>,
+    ) -> Result<PdRpcClient<Cod>> {
         PdRpcClient::new(
             config.clone(),
             |security_mgr| TikvConnect::new(security_mgr, config.timeout),
             |security_mgr| RetryClient::connect(pd_endpoints, security_mgr, config.timeout),
-            enable_codec,
+            enable_mvcc_codec,
+            codec,
         )
         .await
     }
 }
 
-impl<KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<KvC, Cl> {
+impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<Cod, KvC, Cl> {
     pub async fn new<PdFut, MakeKvC, MakePd>(
         config: Config,
         kv_connect: MakeKvC,
         pd: MakePd,
-        enable_codec: bool,
-    ) -> Result<PdRpcClient<KvC, Cl>>
+        enable_mvcc_codec: bool,
+        codec: Option<Cod>,
+    ) -> Result<PdRpcClient<Cod, KvC, Cl>>
     where
         PdFut: Future<Output = Result<RetryClient<Cl>>>,
         MakeKvC: FnOnce(Arc<SecurityManager>) -> KvC,
@@ -301,8 +325,9 @@ impl<KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<KvC, Cl> {
             pd: pd.clone(),
             kv_client_cache,
             kv_connect: kv_connect(security_mgr),
-            enable_codec,
+            enable_mvcc_codec,
             region_cache: RegionCache::new(pd),
+            codec,
         })
     }
 
@@ -322,6 +347,10 @@ impl<KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<KvC, Cl> {
             Err(e) => Err(e),
         }
     }
+
+    pub fn set_codec(&mut self, codec: Cod) {
+        self.codec = Some(codec);
+    }
 }
 
 fn make_key_range(start_key: Vec<u8>, end_key: Vec<u8>) -> kvrpcpb::KeyRange {
diff --git a/src/raw/client.rs b/src/raw/client.rs
index 0bdc2f8b..fc733015 100644
--- a/src/raw/client.rs
+++ b/src/raw/client.rs
@@ -15,6 +15,7 @@ use crate::pd::PdClient;
 use crate::pd::PdRpcClient;
 use crate::proto::metapb;
 use crate::raw::lowering::*;
+use crate::request::codec::{ApiV1RawCodec, Codec, EncodedRequest};
 use crate::request::Collect;
 use crate::request::CollectSingle;
 use crate::request::Plan;
@@ -35,7 +36,11 @@ const MAX_RAW_KV_SCAN_LIMIT: u32 = 10240;
 ///
 /// The returned results of raw request methods are [`Future`](std::future::Future)s that must be
 /// awaited to execute.
-pub struct Client<PdC: PdClient = PdRpcClient> {
+pub struct Client<Cod = ApiV1RawCodec, PdC = PdRpcClient<Cod>>
+where
+    Cod: Codec,
+    PdC: PdClient<Codec = Cod>,
+{
     rpc: Arc<PdC>,
     cf: Option<ColumnFamily>,
     backoff: Backoff,
@@ -54,7 +59,7 @@ impl Clone for Client {
     }
 }
 
-impl Client<PdRpcClient> {
+impl Client<ApiV1RawCodec, PdRpcClient<ApiV1RawCodec>> {
     /// Create a raw [`Client`] and connect to the TiKV cluster.
     ///
     /// Because TiKV is managed by a [PD](https://github.com/pingcap/pd/) cluster, the endpoints for
@@ -100,7 +105,10 @@ impl Client<PdRpcClient> {
         config: Config,
     ) -> Result<Self> {
         let pd_endpoints: Vec<String> = pd_endpoints.into_iter().map(Into::into).collect();
-        let rpc = Arc::new(PdRpcClient::connect(&pd_endpoints, config, false).await?);
+        let rpc = Arc::new(
+            PdRpcClient::connect(&pd_endpoints, config, false, Some(ApiV1RawCodec::default()))
+                .await?,
+        );
         Ok(Client {
             rpc,
             cf: None,
@@ -142,7 +150,9 @@ impl Client<PdRpcClient> {
             atomic: self.atomic,
         }
     }
+}
 
+impl<Cod: Codec> Client<Cod, PdRpcClient<Cod>> {
     /// Set the [`Backoff`] strategy for retrying requests.
     /// The default strategy is [`DEFAULT_REGION_BACKOFF`](crate::backoff::DEFAULT_REGION_BACKOFF).
     /// See [`Backoff`] for more information.
@@ -189,7 +199,7 @@ impl Client<PdRpcClient> {
     }
 }
 
-impl<PdC: PdClient> Client<PdC> {
+impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
     /// Create a new 'get' request.
     ///
     /// Once resolved this request will result in the fetching of the value associated with the
@@ -211,7 +221,8 @@ impl<PdC: PdClient> Client<PdC> {
     pub async fn get(&self, key: impl Into<Key>) -> Result<Option<Value>> {
         debug!("invoking raw get request");
         let request = new_raw_get_request(key.into(), self.cf.clone());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .post_process_default()
@@ -243,7 +254,8 @@ impl<PdC: PdClient> Client<PdC> {
     ) -> Result<Vec<KvPair>> {
         debug!("invoking raw batch_get request");
         let request = new_raw_batch_get_request(keys.into_iter().map(Into::into), self.cf.clone());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(Collect)
             .plan();
@@ -271,7 +283,8 @@ impl<PdC: PdClient> Client<PdC> {
     pub async fn put(&self, key: impl Into<Key>, value: impl Into<Value>) -> Result<()> {
         debug!("invoking raw put request");
         let request = new_raw_put_request(key.into(), value.into(), self.cf.clone(), self.atomic);
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .extract_error()
@@ -307,7 +320,8 @@ impl<PdC: PdClient> Client<PdC> {
             self.cf.clone(),
             self.atomic,
         );
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -335,7 +349,8 @@ impl<PdC: PdClient> Client<PdC> {
     pub async fn delete(&self, key: impl Into<Key>) -> Result<()> {
         debug!("invoking raw delete request");
         let request = new_raw_delete_request(key.into(), self.cf.clone(), self.atomic);
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .extract_error()
@@ -366,7 +381,8 @@ impl<PdC: PdClient> Client<PdC> {
         self.assert_non_atomic()?;
         let request =
             new_raw_batch_delete_request(keys.into_iter().map(Into::into), self.cf.clone());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -393,7 +409,8 @@ impl<PdC: PdClient> Client<PdC> {
         debug!("invoking raw delete_range request");
         self.assert_non_atomic()?;
         let request = new_raw_delete_range_request(range.into(), self.cf.clone());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -549,7 +566,8 @@ impl<PdC: PdClient> Client<PdC> {
             previous_value.into(),
             self.cf.clone(),
         );
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .post_process_default()
@@ -572,7 +590,8 @@ impl<PdC: PdClient> Client<PdC> {
             ranges.into_iter().map(Into::into),
             request_builder,
         );
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .preserve_shard()
             .retry_multi_region(self.backoff.clone())
             .post_process_default()
@@ -606,7 +625,8 @@ impl<PdC: PdClient> Client<PdC> {
         while cur_limit > 0 {
             let request =
                 new_raw_scan_request(cur_range.clone(), cur_limit, key_only, self.cf.clone());
-            let resp = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+            let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+            let resp = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
                 .single_region_with_store(region_store.clone())
                 .await?
                 .plan()
@@ -661,7 +681,8 @@ impl<PdC: PdClient> Client<PdC> {
             key_only,
             self.cf.clone(),
         );
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
             .retry_multi_region(self.backoff.clone())
             .merge(Collect)
             .plan();
diff --git a/src/raw/requests.rs b/src/raw/requests.rs
index 107b8807..23bfce73 100644
--- a/src/raw/requests.rs
+++ b/src/raw/requests.rs
@@ -13,6 +13,7 @@ use super::RawRpcRequest;
 use crate::collect_first;
 use crate::pd::PdClient;
 use crate::proto::kvrpcpb;
+use crate::proto::kvrpcpb::ApiVersion;
 use crate::proto::metapb;
 use crate::proto::tikvpb::tikv_client::TikvClient;
 use crate::request::plan::ResponseWithShard;
@@ -161,7 +162,7 @@ impl Shardable for kvrpcpb::RawBatchPutRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         self.pairs = shard;
         Ok(())
     }
@@ -292,7 +293,7 @@ impl Shardable for kvrpcpb::RawBatchScanRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         self.ranges = shard;
         Ok(())
     }
@@ -397,6 +398,10 @@ impl Request for RawCoprocessorRequest {
     fn set_context(&mut self, context: kvrpcpb::Context) {
         self.inner.set_context(context);
     }
+
+    fn set_api_version(&mut self, api_version: ApiVersion) {
+        self.inner.set_api_version(api_version);
+    }
 }
 
 impl KvRequest for RawCoprocessorRequest {
@@ -496,6 +501,7 @@ mod test {
     use crate::mock::MockKvClient;
     use crate::mock::MockPdClient;
     use crate::proto::kvrpcpb;
+    use crate::request::codec::EncodedRequest;
     use crate::request::Plan;
     use crate::Key;
 
@@ -530,7 +536,8 @@ mod test {
             key_only: true,
             ..Default::default()
         };
-        let plan = crate::request::PlanBuilder::new(client, scan)
+        let encoded_scan = EncodedRequest::new(scan, client.get_codec());
+        let plan = crate::request::PlanBuilder::new(client, encoded_scan)
             .resolve_lock(OPTIMISTIC_BACKOFF)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .merge(Collect)
diff --git a/src/request/codec.rs b/src/request/codec.rs
new file mode 100644
index 00000000..a409a8e7
--- /dev/null
+++ b/src/request/codec.rs
@@ -0,0 +1,54 @@
+// Copyright 2023 TiKV Project Authors. Licensed under Apache-2.0.
+
+use crate::proto::kvrpcpb;
+use crate::request::KvRequest;
+
+pub trait Codec: Clone + Sync + Send + 'static {
+    fn encode_request<R: KvRequest>(&self, _req: &mut R) {}
+    // TODO: fn decode_response()
+}
+
+#[derive(Clone, Default)]
+pub struct ApiV1TxnCodec {}
+
+impl Codec for ApiV1TxnCodec {}
+
+#[derive(Clone, Default)]
+pub struct ApiV1RawCodec {}
+
+impl Codec for ApiV1RawCodec {}
+
+#[derive(Clone)]
+pub struct ApiV2TxnCodec {
+    _keyspace_id: u32,
+}
+
+impl ApiV2TxnCodec {
+    pub fn new(keyspace_id: u32) -> Self {
+        Self {
+            _keyspace_id: keyspace_id,
+        }
+    }
+}
+
+impl Codec for ApiV2TxnCodec {
+    fn encode_request<R: KvRequest>(&self, req: &mut R) {
+        req.set_api_version(kvrpcpb::ApiVersion::V2);
+        // TODO: req.encode_request(self);
+    }
+}
+
+// TODO: pub struct ApiV2RawCodec
+
+// EncodeRequest is just a type wrapper to avoid passing not encoded request to `PlanBuilder` by mistake.
+#[derive(Clone)]
+pub struct EncodedRequest<Req: KvRequest> {
+    pub inner: Req,
+}
+
+impl<Req: KvRequest> EncodedRequest<Req> {
+    pub fn new<C: Codec>(mut req: Req, codec: &C) -> Self {
+        codec.encode_request(&mut req);
+        Self { inner: req }
+    }
+}
diff --git a/src/request/mod.rs b/src/request/mod.rs
index a1ac759e..429adea5 100644
--- a/src/request/mod.rs
+++ b/src/request/mod.rs
@@ -32,6 +32,7 @@ use crate::store::HasKeyErrors;
 use crate::store::Request;
 use crate::transaction::HasLocks;
 
+pub mod codec;
 pub mod plan;
 mod plan_builder;
 mod shard;
@@ -41,6 +42,9 @@ mod shard;
 pub trait KvRequest: Request + Sized + Clone + Sync + Send + 'static {
     /// The expected response to the request.
     type Response: HasKeyErrors + HasLocks + Clone + Send + 'static;
+
+    // TODO: fn encode_request()
+    // TODO: fn decode_response()
 }
 
 #[derive(Clone, Debug, new, Eq, PartialEq)]
@@ -87,9 +91,12 @@ mod test {
     use super::*;
     use crate::mock::MockKvClient;
     use crate::mock::MockPdClient;
+    use crate::pd::PdClient;
     use crate::proto::kvrpcpb;
+    use crate::proto::kvrpcpb::ApiVersion;
     use crate::proto::pdpb::Timestamp;
     use crate::proto::tikvpb::tikv_client::TikvClient;
+    use crate::request::codec::EncodedRequest;
     use crate::store::store_stream_for_keys;
     use crate::store::HasRegionError;
     use crate::transaction::lowering::new_commit_request;
@@ -138,6 +145,8 @@ mod test {
             fn set_context(&mut self, _: kvrpcpb::Context) {
                 unreachable!();
             }
+
+            fn set_api_version(&mut self, _api_version: ApiVersion) {}
         }
 
         #[async_trait]
@@ -183,7 +192,8 @@ mod test {
             |_: &dyn Any| Ok(Box::new(MockRpcResponse) as Box<dyn Any>),
         )));
 
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
+        let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .resolve_lock(Backoff::no_jitter_backoff(1, 1, 3))
             .retry_multi_region(Backoff::no_jitter_backoff(1, 1, 3))
             .extract_error()
@@ -207,16 +217,17 @@ mod test {
 
         let key: Key = "key".to_owned().into();
         let req = new_commit_request(iter::once(key), Timestamp::default(), Timestamp::default());
+        let encoded_req = EncodedRequest::new(req, pd_client.get_codec());
 
         // does not extract error
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req.clone())
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req.clone())
             .resolve_lock(OPTIMISTIC_BACKOFF)
             .retry_multi_region(OPTIMISTIC_BACKOFF)
             .plan();
         assert!(plan.execute().await.is_ok());
 
         // extract error
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .resolve_lock(OPTIMISTIC_BACKOFF)
             .retry_multi_region(OPTIMISTIC_BACKOFF)
             .extract_error()
diff --git a/src/request/plan_builder.rs b/src/request/plan_builder.rs
index 5ce2350c..88a5e9ad 100644
--- a/src/request/plan_builder.rs
+++ b/src/request/plan_builder.rs
@@ -6,6 +6,7 @@ use std::sync::Arc;
 use super::plan::PreserveShard;
 use crate::backoff::Backoff;
 use crate::pd::PdClient;
+use crate::request::codec::EncodedRequest;
 use crate::request::plan::CleanupLocks;
 use crate::request::shard::HasNextBatch;
 use crate::request::DefaultProcessor;
@@ -46,11 +47,11 @@ pub struct Targetted;
 impl PlanBuilderPhase for Targetted {}
 
 impl<PdC: PdClient, Req: KvRequest> PlanBuilder<PdC, Dispatch<Req>, NoTarget> {
-    pub fn new(pd_client: Arc<PdC>, request: Req) -> Self {
+    pub fn new(pd_client: Arc<PdC>, encoded_request: EncodedRequest<Req>) -> Self {
         PlanBuilder {
             pd_client,
             plan: Dispatch {
-                request,
+                request: encoded_request.inner,
                 kv_client: None,
             },
             phantom: PhantomData,
diff --git a/src/request/shard.rs b/src/request/shard.rs
index aaefab72..7c78743d 100644
--- a/src/request/shard.rs
+++ b/src/request/shard.rs
@@ -163,7 +163,7 @@ macro_rules! shardable_key {
                 mut shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.context = Some(store.region_with_leader.context()?);
+                self.set_context(store.region_with_leader.context()?);
                 assert!(shard.len() == 1);
                 self.key = shard.pop().unwrap();
                 Ok(())
@@ -196,7 +196,7 @@ macro_rules! shardable_keys {
                 shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.context = Some(store.region_with_leader.context()?);
+                self.set_context(store.region_with_leader.context()?);
                 self.keys = shard.into_iter().map(Into::into).collect();
                 Ok(())
             }
@@ -225,7 +225,7 @@ macro_rules! shardable_range {
                 shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.context = Some(store.region_with_leader.context()?);
+                self.set_context(store.region_with_leader.context()?);
 
                 self.start_key = shard.0.into();
                 self.end_key = shard.1.into();
diff --git a/src/store/request.rs b/src/store/request.rs
index 5060eb01..2f1a31a0 100644
--- a/src/store/request.rs
+++ b/src/store/request.rs
@@ -21,7 +21,10 @@ pub trait Request: Any + Sync + Send + 'static {
     ) -> Result<Box<dyn Any>>;
     fn label(&self) -> &'static str;
     fn as_any(&self) -> &dyn Any;
+    /// Set the context for the request.
+    /// Should always use `set_context` other than modify the `self.context` directly.
     fn set_context(&mut self, context: kvrpcpb::Context);
+    fn set_api_version(&mut self, api_version: kvrpcpb::ApiVersion);
 }
 
 macro_rules! impl_request {
@@ -52,7 +55,18 @@ macro_rules! impl_request {
             }
 
             fn set_context(&mut self, context: kvrpcpb::Context) {
+                let api_version = self
+                    .context
+                    .as_ref()
+                    .map(|c| c.api_version)
+                    .unwrap_or_default();
                 self.context = Some(context);
+                self.set_api_version(kvrpcpb::ApiVersion::from_i32(api_version).unwrap());
+            }
+
+            fn set_api_version(&mut self, api_version: kvrpcpb::ApiVersion) {
+                let context = self.context.get_or_insert(kvrpcpb::Context::default());
+                context.api_version = api_version.into();
             }
         }
     };
diff --git a/src/transaction/client.rs b/src/transaction/client.rs
index 64d32451..610ea065 100644
--- a/src/transaction/client.rs
+++ b/src/transaction/client.rs
@@ -10,6 +10,7 @@ use crate::config::Config;
 use crate::pd::PdClient;
 use crate::pd::PdRpcClient;
 use crate::proto::pdpb::Timestamp;
+use crate::request::codec::{ApiV1TxnCodec, ApiV2TxnCodec, Codec, EncodedRequest};
 use crate::request::plan::CleanupLocksResult;
 use crate::request::Plan;
 use crate::timestamp::TimestampExt;
@@ -42,11 +43,11 @@ const SCAN_LOCK_BATCH_SIZE: u32 = 1024;
 ///
 /// The returned results of transactional requests are [`Future`](std::future::Future)s that must be
 /// awaited to execute.
-pub struct Client {
-    pd: Arc<PdRpcClient>,
+pub struct Client<Cod: Codec = ApiV1TxnCodec> {
+    pd: Arc<PdRpcClient<Cod>>,
 }
 
-impl Clone for Client {
+impl<Cod: Codec> Clone for Client<Cod> {
     fn clone(&self) -> Self {
         Self {
             pd: self.pd.clone(),
@@ -54,7 +55,7 @@ impl Clone for Client {
     }
 }
 
-impl Client {
+impl Client<ApiV1TxnCodec> {
     /// Create a transactional [`Client`] and connect to the TiKV cluster.
     ///
     /// Because TiKV is managed by a [PD](https://github.com/pingcap/pd/) cluster, the endpoints for
@@ -71,7 +72,6 @@ impl Client {
     /// # });
     /// ```
     pub async fn new<S: Into<String>>(pd_endpoints: Vec<S>) -> Result<Client> {
-        // debug!("creating transactional client");
         Self::new_with_config(pd_endpoints, Config::default()).await
     }
 
@@ -100,9 +100,35 @@ impl Client {
         pd_endpoints: Vec<S>,
         config: Config,
     ) -> Result<Client> {
+        Self::new_with_codec(pd_endpoints, config, ApiV1TxnCodec::default()).await
+    }
+}
+
+impl Client<ApiV2TxnCodec> {
+    pub async fn new_with_config_v2<S: Into<String>>(
+        _keyspace_name: &str,
+        pd_endpoints: Vec<S>,
+        config: Config,
+    ) -> Result<Client<ApiV2TxnCodec>> {
+        debug!("creating new transactional client APIv2");
+        let pd_endpoints: Vec<String> = pd_endpoints.into_iter().map(Into::into).collect();
+        let mut pd = PdRpcClient::connect(&pd_endpoints, config, true, None).await?;
+        let keyspace_id = 0; // TODO: get keyspace_id by pd.get_keyspace(keyspace_name)
+        pd.set_codec(ApiV2TxnCodec::new(keyspace_id));
+        Ok(Client { pd: Arc::new(pd) })
+    }
+}
+
+impl<Cod: Codec> Client<Cod> {
+    pub async fn new_with_codec<S: Into<String>>(
+        pd_endpoints: Vec<S>,
+        config: Config,
+        codec: Cod,
+    ) -> Result<Client<Cod>> {
         debug!("creating new transactional client");
         let pd_endpoints: Vec<String> = pd_endpoints.into_iter().map(Into::into).collect();
-        let pd = Arc::new(PdRpcClient::connect(&pd_endpoints, config, true).await?);
+        let pd =
+            Arc::new(PdRpcClient::<Cod>::connect(&pd_endpoints, config, true, Some(codec)).await?);
         Ok(Client { pd })
     }
 
@@ -126,7 +152,7 @@ impl Client {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_optimistic(&self) -> Result<Transaction> {
+    pub async fn begin_optimistic(&self) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
         debug!("creating new optimistic transaction");
         let timestamp = self.current_timestamp().await?;
         Ok(self.new_transaction(timestamp, TransactionOptions::new_optimistic()))
@@ -149,7 +175,7 @@ impl Client {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_pessimistic(&self) -> Result<Transaction> {
+    pub async fn begin_pessimistic(&self) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
         debug!("creating new pessimistic transaction");
         let timestamp = self.current_timestamp().await?;
         Ok(self.new_transaction(timestamp, TransactionOptions::new_pessimistic()))
@@ -172,14 +198,21 @@ impl Client {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_with_options(&self, options: TransactionOptions) -> Result<Transaction> {
+    pub async fn begin_with_options(
+        &self,
+        options: TransactionOptions,
+    ) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
         debug!("creating new customized transaction");
         let timestamp = self.current_timestamp().await?;
         Ok(self.new_transaction(timestamp, options))
     }
 
     /// Create a new [`Snapshot`](Snapshot) at the given [`Timestamp`](Timestamp).
-    pub fn snapshot(&self, timestamp: Timestamp, options: TransactionOptions) -> Snapshot {
+    pub fn snapshot(
+        &self,
+        timestamp: Timestamp,
+        options: TransactionOptions,
+    ) -> Snapshot<Cod, PdRpcClient<Cod>> {
         debug!("creating new snapshot");
         Snapshot::new(self.new_transaction(timestamp, options.read_only()))
     }
@@ -246,7 +279,8 @@ impl Client {
         let ctx = ResolveLocksContext::default();
         let backoff = Backoff::equal_jitter_backoff(100, 10000, 50);
         let req = new_scan_lock_request(range.into(), safepoint, options.batch_size);
-        let plan = crate::request::PlanBuilder::new(self.pd.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.pd.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.pd.clone(), encoded_req)
             .cleanup_locks(ctx.clone(), options, backoff)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .extract_error()
@@ -265,14 +299,19 @@ impl Client {
         batch_size: u32,
     ) -> Result<Vec<crate::proto::kvrpcpb::LockInfo>> {
         let req = new_scan_lock_request(range.into(), safepoint, batch_size);
-        let plan = crate::request::PlanBuilder::new(self.pd.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.pd.get_codec());
+        let plan = crate::request::PlanBuilder::new(self.pd.clone(), encoded_req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .merge(crate::request::Collect)
             .plan();
         plan.execute().await
     }
 
-    fn new_transaction(&self, timestamp: Timestamp, options: TransactionOptions) -> Transaction {
+    fn new_transaction(
+        &self,
+        timestamp: Timestamp,
+        options: TransactionOptions,
+    ) -> Transaction<Cod, PdRpcClient<Cod>> {
         Transaction::new(timestamp, self.pd.clone(), options)
     }
 }
diff --git a/src/transaction/lock.rs b/src/transaction/lock.rs
index 25522422..0ccb5e46 100644
--- a/src/transaction/lock.rs
+++ b/src/transaction/lock.rs
@@ -17,6 +17,7 @@ use crate::proto::kvrpcpb;
 use crate::proto::kvrpcpb::TxnInfo;
 use crate::proto::pdpb::Timestamp;
 use crate::region::RegionVerId;
+use crate::request::codec::EncodedRequest;
 use crate::request::Collect;
 use crate::request::CollectSingle;
 use crate::request::Plan;
@@ -77,7 +78,8 @@ pub async fn resolve_locks(
             Some(&commit_version) => commit_version,
             None => {
                 let request = requests::new_cleanup_request(lock.primary_lock, lock.lock_version);
-                let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
+                let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
+                let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
                     .resolve_lock(OPTIMISTIC_BACKOFF)
                     .retry_multi_region(DEFAULT_REGION_BACKOFF)
                     .merge(CollectSingle)
@@ -118,8 +120,8 @@ async fn resolve_lock_with_retry(
         let store = pd_client.clone().store_for_key(key.into()).await?;
         let ver_id = store.region_with_leader.ver_id();
         let request = requests::new_resolve_lock_request(start_version, commit_version);
-        // The only place where single-region is used
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
+        let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .single_region_with_store(store)
             .await?
             .resolve_lock(Backoff::no_backoff())
@@ -359,7 +361,8 @@ impl LockResolver {
             force_sync_commit,
             resolving_pessimistic_lock,
         );
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req)
+        let encoded_req = EncodedRequest::new(req, pd_client.get_codec());
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .merge(CollectSingle)
             .extract_error()
@@ -383,7 +386,8 @@ impl LockResolver {
         txn_id: u64,
     ) -> Result<SecondaryLocksStatus> {
         let req = new_check_secondary_locks_request(keys, txn_id);
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req)
+        let encoded_req = EncodedRequest::new(req, pd_client.get_codec());
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .extract_error()
             .merge(Collect)
@@ -399,7 +403,8 @@ impl LockResolver {
     ) -> Result<RegionVerId> {
         let ver_id = store.region_with_leader.ver_id();
         let request = requests::new_batch_resolve_lock_request(txn_infos.clone());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
+        let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
             .single_region_with_store(store.clone())
             .await?
             .extract_error()
diff --git a/src/transaction/requests.rs b/src/transaction/requests.rs
index 9cc4993f..bd3852e3 100644
--- a/src/transaction/requests.rs
+++ b/src/transaction/requests.rs
@@ -38,6 +38,7 @@ use crate::shardable_range;
 use crate::store::store_stream_for_keys;
 use crate::store::store_stream_for_range;
 use crate::store::RegionStore;
+use crate::store::Request;
 use crate::timestamp::TimestampExt;
 use crate::transaction::HasLocks;
 use crate::util::iter::FlatMapOkIterExt;
@@ -294,7 +295,7 @@ impl Shardable for kvrpcpb::PrewriteRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
 
         // Only need to set secondary keys if we're sending the primary key.
         if self.use_async_commit && !self.mutations.iter().any(|m| m.key == self.primary_lock) {
@@ -361,7 +362,7 @@ impl Shardable for kvrpcpb::CommitRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         self.keys = shard.into_iter().map(Into::into).collect();
         Ok(())
     }
@@ -452,7 +453,7 @@ impl Shardable for kvrpcpb::PessimisticLockRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         self.mutations = shard;
         Ok(())
     }
@@ -553,7 +554,7 @@ impl Shardable for kvrpcpb::ScanLockRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         self.start_key = shard.0;
         Ok(())
     }
@@ -614,7 +615,7 @@ impl Shardable for kvrpcpb::TxnHeartBeatRequest {
     }
 
     fn apply_shard(&mut self, mut shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         assert!(shard.len() == 1);
         self.primary_lock = shard.pop().unwrap();
         Ok(())
@@ -672,7 +673,7 @@ impl Shardable for kvrpcpb::CheckTxnStatusRequest {
     }
 
     fn apply_shard(&mut self, mut shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.context = Some(store.region_with_leader.context()?);
+        self.set_context(store.region_with_leader.context()?);
         assert!(shard.len() == 1);
         self.primary_key = shard.pop().unwrap();
         Ok(())
diff --git a/src/transaction/snapshot.rs b/src/transaction/snapshot.rs
index 5694614b..a8aa9464 100644
--- a/src/transaction/snapshot.rs
+++ b/src/transaction/snapshot.rs
@@ -2,7 +2,11 @@
 
 use derive_new::new;
 use log::debug;
+use std::marker::PhantomData;
 
+use crate::codec::ApiV1TxnCodec;
+use crate::pd::{PdClient, PdRpcClient};
+use crate::request::codec::Codec;
 use crate::BoundRange;
 use crate::Key;
 use crate::KvPair;
@@ -18,11 +22,12 @@ use crate::Value;
 ///
 /// See the [Transaction](struct@crate::Transaction) docs for more information on the methods.
 #[derive(new)]
-pub struct Snapshot {
-    transaction: Transaction,
+pub struct Snapshot<Cod: Codec = ApiV1TxnCodec, PdC: PdClient = PdRpcClient<Cod>> {
+    transaction: Transaction<Cod, PdC>,
+    phantom: PhantomData<Cod>,
 }
 
-impl Snapshot {
+impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Snapshot<Cod, PdC> {
     /// Get the value associated with the given key.
     pub async fn get(&mut self, key: impl Into<Key>) -> Result<Option<Value>> {
         debug!("invoking get request on snapshot");
diff --git a/src/transaction/transaction.rs b/src/transaction/transaction.rs
index 44532f7e..9317e171 100644
--- a/src/transaction/transaction.rs
+++ b/src/transaction/transaction.rs
@@ -1,6 +1,7 @@
 // Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.
 
 use std::iter;
+use std::marker::PhantomData;
 use std::sync::Arc;
 use std::time::Instant;
 
@@ -14,10 +15,12 @@ use tokio::time::Duration;
 
 use crate::backoff::Backoff;
 use crate::backoff::DEFAULT_REGION_BACKOFF;
+use crate::codec::ApiV1TxnCodec;
 use crate::pd::PdClient;
 use crate::pd::PdRpcClient;
 use crate::proto::kvrpcpb;
 use crate::proto::pdpb::Timestamp;
+use crate::request::codec::{Codec, EncodedRequest};
 use crate::request::Collect;
 use crate::request::CollectError;
 use crate::request::CollectSingle;
@@ -73,7 +76,7 @@ use crate::Value;
 /// txn.commit().await.unwrap();
 /// # });
 /// ```
-pub struct Transaction<PdC: PdClient = PdRpcClient> {
+pub struct Transaction<Cod: Codec = ApiV1TxnCodec, PdC: PdClient = PdRpcClient<Cod>> {
     status: Arc<RwLock<TransactionStatus>>,
     timestamp: Timestamp,
     buffer: Buffer,
@@ -81,14 +84,15 @@ pub struct Transaction<PdC: PdClient = PdRpcClient> {
     options: TransactionOptions,
     is_heartbeat_started: bool,
     start_instant: Instant,
+    phantom: PhantomData<Cod>,
 }
 
-impl<PdC: PdClient> Transaction<PdC> {
+impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
     pub(crate) fn new(
         timestamp: Timestamp,
         rpc: Arc<PdC>,
         options: TransactionOptions,
-    ) -> Transaction<PdC> {
+    ) -> Transaction<Cod, PdC> {
         let status = if options.read_only {
             TransactionStatus::ReadOnly
         } else {
@@ -102,6 +106,7 @@ impl<PdC: PdClient> Transaction<PdC> {
             options,
             is_heartbeat_started: false,
             start_instant: std::time::Instant::now(),
+            phantom: PhantomData,
         }
     }
 
@@ -134,7 +139,8 @@ impl<PdC: PdClient> Transaction<PdC> {
         self.buffer
             .get_or_else(key, |key| async move {
                 let request = new_get_request(key, timestamp);
-                let plan = PlanBuilder::new(rpc, request)
+                let encoded_req = EncodedRequest::new(request, rpc.get_codec());
+                let plan = PlanBuilder::new(rpc, encoded_req)
                     .resolve_lock(retry_options.lock_backoff)
                     .retry_multi_region(DEFAULT_REGION_BACKOFF)
                     .merge(CollectSingle)
@@ -264,7 +270,8 @@ impl<PdC: PdClient> Transaction<PdC> {
         self.buffer
             .batch_get_or_else(keys.into_iter().map(|k| k.into()), move |keys| async move {
                 let request = new_batch_get_request(keys, timestamp);
-                let plan = PlanBuilder::new(rpc, request)
+                let encoded_req = EncodedRequest::new(request, rpc.get_codec());
+                let plan = PlanBuilder::new(rpc, encoded_req)
                     .resolve_lock(retry_options.lock_backoff)
                     .retry_multi_region(retry_options.region_backoff)
                     .merge(Collect)
@@ -691,7 +698,8 @@ impl<PdC: PdClient> Transaction<PdC> {
             primary_key,
             self.start_instant.elapsed().as_millis() as u64 + MAX_TTL,
         );
-        let plan = PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .merge(CollectSingle)
@@ -721,7 +729,8 @@ impl<PdC: PdClient> Transaction<PdC> {
                 move |new_range, new_limit| async move {
                     let request =
                         new_scan_request(new_range, timestamp, new_limit, key_only, reverse);
-                    let plan = PlanBuilder::new(rpc, request)
+                    let encoded_req = EncodedRequest::new(request, rpc.get_codec());
+                    let plan = PlanBuilder::new(rpc, encoded_req)
                         .resolve_lock(retry_options.lock_backoff)
                         .retry_multi_region(retry_options.region_backoff)
                         .merge(Collect)
@@ -776,7 +785,8 @@ impl<PdC: PdClient> Transaction<PdC> {
             for_update_ts.clone(),
             need_value,
         );
-        let plan = PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .preserve_shard()
             .retry_multi_region_preserve_results(self.options.retry_options.region_backoff.clone())
@@ -830,7 +840,8 @@ impl<PdC: PdClient> Transaction<PdC> {
             start_version,
             for_update_ts,
         );
-        let plan = PlanBuilder::new(self.rpc.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .extract_error()
@@ -900,7 +911,8 @@ impl<PdC: PdClient> Transaction<PdC> {
                     primary_key.clone(),
                     start_instant.elapsed().as_millis() as u64 + MAX_TTL,
                 );
-                let plan = PlanBuilder::new(rpc.clone(), request)
+                let encoded_req = EncodedRequest::new(request, rpc.get_codec());
+                let plan = PlanBuilder::new(rpc.clone(), encoded_req)
                     .retry_multi_region(region_backoff.clone())
                     .merge(CollectSingle)
                     .plan();
@@ -917,7 +929,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     }
 }
 
-impl<PdC: PdClient> Drop for Transaction<PdC> {
+impl<Cod: Codec, PdC: PdClient> Drop for Transaction<Cod, PdC> {
     fn drop(&mut self) {
         debug!("dropping transaction");
         if std::thread::panicking() {
@@ -1209,7 +1221,8 @@ impl<PdC: PdClient> Committer<PdC> {
             .collect();
         // FIXME set max_commit_ts and min_commit_ts
 
-        let plan = PlanBuilder::new(self.rpc.clone(), request)
+        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .merge(CollectError)
@@ -1249,7 +1262,8 @@ impl<PdC: PdClient> Committer<PdC> {
             self.start_version.clone(),
             commit_version.clone(),
         );
-        let plan = PlanBuilder::new(self.rpc.clone(), req)
+        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .extract_error()
@@ -1313,7 +1327,8 @@ impl<PdC: PdClient> Committer<PdC> {
                 .filter(|key| &primary_key != key);
             new_commit_request(keys, self.start_version, commit_version)
         };
-        let plan = PlanBuilder::new(self.rpc, req)
+        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+        let plan = PlanBuilder::new(self.rpc, encoded_req)
             .resolve_lock(self.options.retry_options.lock_backoff)
             .retry_multi_region(self.options.retry_options.region_backoff)
             .extract_error()
@@ -1334,7 +1349,8 @@ impl<PdC: PdClient> Committer<PdC> {
         match self.options.kind {
             TransactionKind::Optimistic => {
                 let req = new_batch_rollback_request(keys, self.start_version);
-                let plan = PlanBuilder::new(self.rpc, req)
+                let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+                let plan = PlanBuilder::new(self.rpc, encoded_req)
                     .resolve_lock(self.options.retry_options.lock_backoff)
                     .retry_multi_region(self.options.retry_options.region_backoff)
                     .extract_error()
@@ -1343,7 +1359,8 @@ impl<PdC: PdClient> Committer<PdC> {
             }
             TransactionKind::Pessimistic(for_update_ts) => {
                 let req = new_pessimistic_rollback_request(keys, self.start_version, for_update_ts);
-                let plan = PlanBuilder::new(self.rpc, req)
+                let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
+                let plan = PlanBuilder::new(self.rpc, encoded_req)
                     .resolve_lock(self.options.retry_options.lock_backoff)
                     .retry_multi_region(self.options.retry_options.region_backoff)
                     .extract_error()