diff --git a/src/lib.rs b/src/lib.rs
index a2acf57b..60dc2956 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -94,8 +94,6 @@
 
 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)]
@@ -106,6 +104,7 @@ mod compat;
 mod config;
 mod kv;
 mod pd;
+mod proto;
 mod region;
 mod region_cache;
 mod stats;
@@ -146,8 +145,6 @@ 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 f9c94aef..38fea6b2 100644
--- a/src/mock.rs
+++ b/src/mock.rs
@@ -18,7 +18,6 @@ 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::KvConnect;
 use crate::store::RegionStore;
 use crate::store::Request;
@@ -31,7 +30,7 @@ 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<ApiV1TxnCodec, MockKvConnect, MockCluster> {
+pub async fn pd_rpc_client() -> PdRpcClient<MockKvConnect, MockCluster> {
     let config = Config::default();
     PdRpcClient::new(
         config.clone(),
@@ -44,7 +43,6 @@ pub async fn pd_rpc_client() -> PdRpcClient<ApiV1TxnCodec, MockKvConnect, MockCl
             ))
         },
         false,
-        Some(ApiV1TxnCodec::default()),
     )
     .await
     .unwrap()
@@ -73,18 +71,9 @@ 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]
@@ -113,7 +102,6 @@ impl MockPdClient {
     pub fn default() -> MockPdClient {
         MockPdClient {
             client: MockKvClient::default(),
-            codec: ApiV1TxnCodec::default(),
         }
     }
 
@@ -177,7 +165,6 @@ 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> {
@@ -227,8 +214,4 @@ 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 5461cb57..8eb4aa34 100644
--- a/src/pd/client.rs
+++ b/src/pd/client.rs
@@ -20,7 +20,6 @@ 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::KvConnect;
 use crate::store::RegionStore;
 use crate::store::TikvConnect;
@@ -51,7 +50,6 @@ 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).
@@ -193,11 +191,8 @@ pub trait PdClient: Send + Sync + 'static {
         .boxed()
     }
 
-    fn decode_region(
-        mut region: RegionWithLeader,
-        enable_mvcc_codec: bool,
-    ) -> Result<RegionWithLeader> {
-        if enable_mvcc_codec {
+    fn decode_region(mut region: RegionWithLeader, enable_codec: bool) -> Result<RegionWithLeader> {
+        if enable_codec {
             codec::decode_bytes_in_place(&mut region.region.start_key, false)?;
             codec::decode_bytes_in_place(&mut region.region.end_key, false)?;
         }
@@ -207,30 +202,20 @@ 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<
-    Cod: Codec = ApiV1TxnCodec,
-    KvC: KvConnect + Send + Sync + 'static = TikvConnect,
-    Cl = Cluster,
-> {
+pub struct PdRpcClient<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_mvcc_codec: bool,
+    enable_codec: bool,
     region_cache: RegionCache<RetryClient<Cl>>,
-    codec: Option<Cod>,
 }
 
 #[async_trait]
-impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<Cod, KvC> {
-    type Codec = Cod;
+impl<KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClient<KvC> {
     type KvClient = KvC::KvClient;
 
     async fn map_region_to_store(self: Arc<Self>, region: RegionWithLeader) -> Result<RegionStore> {
@@ -241,20 +226,20 @@ impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClien
     }
 
     async fn region_for_key(&self, key: &Key) -> Result<RegionWithLeader> {
-        let enable_mvcc_codec = self.enable_mvcc_codec;
-        let key = if enable_mvcc_codec {
+        let enable_codec = self.enable_codec;
+        let key = if enable_codec {
             key.to_encoded()
         } else {
             key.clone()
         };
 
         let region = self.region_cache.get_region_by_key(&key).await?;
-        Self::decode_region(region, enable_mvcc_codec)
+        Self::decode_region(region, enable_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_mvcc_codec)
+        Self::decode_region(region, self.enable_codec)
     }
 
     async fn all_stores(&self) -> Result<Vec<Store>> {
@@ -282,40 +267,31 @@ impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static> PdClient for PdRpcClien
     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<Cod: Codec> PdRpcClient<Cod, TikvConnect, Cluster> {
+impl PdRpcClient<TikvConnect, Cluster> {
     pub async fn connect(
         pd_endpoints: &[String],
         config: Config,
-        enable_mvcc_codec: bool, // TODO: infer from `codec`.
-        codec: Option<Cod>,
-    ) -> Result<PdRpcClient<Cod>> {
+        enable_codec: bool,
+    ) -> Result<PdRpcClient> {
         PdRpcClient::new(
             config.clone(),
             |security_mgr| TikvConnect::new(security_mgr, config.timeout),
             |security_mgr| RetryClient::connect(pd_endpoints, security_mgr, config.timeout),
-            enable_mvcc_codec,
-            codec,
+            enable_codec,
         )
         .await
     }
 }
 
-impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<Cod, KvC, Cl> {
+impl<KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<KvC, Cl> {
     pub async fn new<PdFut, MakeKvC, MakePd>(
         config: Config,
         kv_connect: MakeKvC,
         pd: MakePd,
-        enable_mvcc_codec: bool,
-        codec: Option<Cod>,
-    ) -> Result<PdRpcClient<Cod, KvC, Cl>>
+        enable_codec: bool,
+    ) -> Result<PdRpcClient<KvC, Cl>>
     where
         PdFut: Future<Output = Result<RetryClient<Cl>>>,
         MakeKvC: FnOnce(Arc<SecurityManager>) -> KvC,
@@ -337,9 +313,8 @@ impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<Cod, Kv
             pd: pd.clone(),
             kv_client_cache,
             kv_connect: kv_connect(security_mgr),
-            enable_mvcc_codec,
+            enable_codec,
             region_cache: RegionCache::new(pd),
-            codec,
         })
     }
 
@@ -359,10 +334,6 @@ impl<Cod: Codec, KvC: KvConnect + Send + Sync + 'static, Cl> PdRpcClient<Cod, Kv
             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 fc733015..0bdc2f8b 100644
--- a/src/raw/client.rs
+++ b/src/raw/client.rs
@@ -15,7 +15,6 @@ 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;
@@ -36,11 +35,7 @@ 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<Cod = ApiV1RawCodec, PdC = PdRpcClient<Cod>>
-where
-    Cod: Codec,
-    PdC: PdClient<Codec = Cod>,
-{
+pub struct Client<PdC: PdClient = PdRpcClient> {
     rpc: Arc<PdC>,
     cf: Option<ColumnFamily>,
     backoff: Backoff,
@@ -59,7 +54,7 @@ impl Clone for Client {
     }
 }
 
-impl Client<ApiV1RawCodec, PdRpcClient<ApiV1RawCodec>> {
+impl Client<PdRpcClient> {
     /// 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
@@ -105,10 +100,7 @@ impl Client<ApiV1RawCodec, PdRpcClient<ApiV1RawCodec>> {
         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, Some(ApiV1RawCodec::default()))
-                .await?,
-        );
+        let rpc = Arc::new(PdRpcClient::connect(&pd_endpoints, config, false).await?);
         Ok(Client {
             rpc,
             cf: None,
@@ -150,9 +142,7 @@ impl Client<ApiV1RawCodec, PdRpcClient<ApiV1RawCodec>> {
             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.
@@ -199,7 +189,7 @@ impl<Cod: Codec> Client<Cod, PdRpcClient<Cod>> {
     }
 }
 
-impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
+impl<PdC: PdClient> Client<PdC> {
     /// Create a new 'get' request.
     ///
     /// Once resolved this request will result in the fetching of the value associated with the
@@ -221,8 +211,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, 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 encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .post_process_default()
@@ -254,8 +243,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, 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 encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .merge(Collect)
             .plan();
@@ -283,8 +271,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, 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 encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .extract_error()
@@ -320,8 +307,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
             self.cf.clone(),
             self.atomic,
         );
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -349,8 +335,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, 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 encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .extract_error()
@@ -381,8 +366,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
         self.assert_non_atomic()?;
         let request =
             new_raw_batch_delete_request(keys.into_iter().map(Into::into), self.cf.clone());
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -409,8 +393,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
         debug!("invoking raw delete_range request");
         self.assert_non_atomic()?;
         let request = new_raw_delete_range_request(range.into(), self.cf.clone());
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .extract_error()
             .plan();
@@ -566,8 +549,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
             previous_value.into(),
             self.cf.clone(),
         );
-        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), req)
             .retry_multi_region(self.backoff.clone())
             .merge(CollectSingle)
             .post_process_default()
@@ -590,8 +572,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
             ranges.into_iter().map(Into::into),
             request_builder,
         );
-        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), req)
             .preserve_shard()
             .retry_multi_region(self.backoff.clone())
             .post_process_default()
@@ -625,8 +606,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
         while cur_limit > 0 {
             let request =
                 new_raw_scan_request(cur_range.clone(), cur_limit, key_only, self.cf.clone());
-            let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-            let resp = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+            let resp = crate::request::PlanBuilder::new(self.rpc.clone(), request)
                 .single_region_with_store(region_store.clone())
                 .await?
                 .plan()
@@ -681,8 +661,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Client<Cod, PdC> {
             key_only,
             self.cf.clone(),
         );
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.rpc.clone(), request)
             .retry_multi_region(self.backoff.clone())
             .merge(Collect)
             .plan();
diff --git a/src/raw/requests.rs b/src/raw/requests.rs
index 0be733cf..f9c64717 100644
--- a/src/raw/requests.rs
+++ b/src/raw/requests.rs
@@ -13,7 +13,6 @@ 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::range_request;
@@ -164,7 +163,7 @@ impl Shardable for kvrpcpb::RawBatchPutRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         self.pairs = shard;
         Ok(())
     }
@@ -297,7 +296,7 @@ impl Shardable for kvrpcpb::RawBatchScanRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         self.ranges = shard;
         Ok(())
     }
@@ -403,7 +402,7 @@ impl Request for RawCoprocessorRequest {
         self.inner.set_context(context);
     }
 
-    fn set_api_version(&mut self, api_version: ApiVersion) {
+    fn set_api_version(&mut self, api_version: kvrpcpb::ApiVersion) {
         self.inner.set_api_version(api_version);
     }
 }
@@ -505,7 +504,6 @@ 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;
 
@@ -540,8 +538,7 @@ mod test {
             key_only: true,
             ..Default::default()
         };
-        let encoded_scan = EncodedRequest::new(scan, client.get_codec());
-        let plan = crate::request::PlanBuilder::new(client, encoded_scan)
+        let plan = crate::request::PlanBuilder::new(client, 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
deleted file mode 100644
index a409a8e7..00000000
--- a/src/request/codec.rs
+++ /dev/null
@@ -1,54 +0,0 @@
-// 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 8c3a45cb..d2d58ddb 100644
--- a/src/request/mod.rs
+++ b/src/request/mod.rs
@@ -33,7 +33,6 @@ use crate::store::Request;
 use crate::store::{HasKeyErrors, Store};
 use crate::transaction::HasLocks;
 
-pub mod codec;
 pub mod plan;
 mod plan_builder;
 mod shard;
@@ -43,9 +42,6 @@ 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()
 }
 
 /// For requests or plans which are handled at TiKV store (other than region) level.
@@ -98,12 +94,9 @@ 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;
@@ -153,7 +146,9 @@ mod test {
                 unreachable!();
             }
 
-            fn set_api_version(&mut self, _api_version: ApiVersion) {}
+            fn set_api_version(&mut self, _: kvrpcpb::ApiVersion) {
+                unreachable!();
+            }
         }
 
         #[async_trait]
@@ -199,8 +194,7 @@ mod test {
             |_: &dyn Any| Ok(Box::new(MockRpcResponse) as Box<dyn Any>),
         )));
 
-        let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
             .resolve_lock(Backoff::no_jitter_backoff(1, 1, 3))
             .retry_multi_region(Backoff::no_jitter_backoff(1, 1, 3))
             .extract_error()
@@ -224,17 +218,16 @@ 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(), encoded_req.clone())
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), 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(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), 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 8e2329e7..96f03dee 100644
--- a/src/request/plan_builder.rs
+++ b/src/request/plan_builder.rs
@@ -6,7 +6,6 @@ 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, RetryableAllStores};
 use crate::request::shard::HasNextBatch;
 use crate::request::Dispatch;
@@ -47,11 +46,11 @@ pub struct Targetted;
 impl PlanBuilderPhase for Targetted {}
 
 impl<PdC: PdClient, Req: KvRequest> PlanBuilder<PdC, Dispatch<Req>, NoTarget> {
-    pub fn new(pd_client: Arc<PdC>, encoded_request: EncodedRequest<Req>) -> Self {
+    pub fn new(pd_client: Arc<PdC>, request: Req) -> Self {
         PlanBuilder {
             pd_client,
             plan: Dispatch {
-                request: encoded_request.inner,
+                request,
                 kv_client: None,
             },
             phantom: PhantomData,
diff --git a/src/request/shard.rs b/src/request/shard.rs
index ec234239..428e5d0e 100644
--- a/src/request/shard.rs
+++ b/src/request/shard.rs
@@ -164,7 +164,7 @@ macro_rules! shardable_key {
                 mut shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.set_context(store.region_with_leader.context()?);
+                self.context = Some(store.region_with_leader.context()?);
                 assert!(shard.len() == 1);
                 self.key = shard.pop().unwrap();
                 Ok(())
@@ -197,7 +197,7 @@ macro_rules! shardable_keys {
                 shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.set_context(store.region_with_leader.context()?);
+                self.context = Some(store.region_with_leader.context()?);
                 self.keys = shard.into_iter().map(Into::into).collect();
                 Ok(())
             }
@@ -257,7 +257,7 @@ macro_rules! shardable_range {
                 shard: Self::Shard,
                 store: &$crate::store::RegionStore,
             ) -> $crate::Result<()> {
-                self.set_context(store.region_with_leader.context()?);
+                self.context = Some(store.region_with_leader.context()?);
 
                 // In a reverse range request, the range is in the meaning of [end_key, start_key), i.e. end_key <= x < start_key.
                 // As a result, after obtaining start_key and end_key from PD, we need to swap their values when assigning them to the request.
diff --git a/src/store/request.rs b/src/store/request.rs
index e11fc8f1..5fa15c6d 100644
--- a/src/store/request.rs
+++ b/src/store/request.rs
@@ -21,8 +21,6 @@ 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);
 }
@@ -55,13 +53,7 @@ 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::try_from(api_version).unwrap());
             }
 
             fn set_api_version(&mut self, api_version: kvrpcpb::ApiVersion) {
diff --git a/src/transaction/client.rs b/src/transaction/client.rs
index 4bcb16d9..1ba0be81 100644
--- a/src/transaction/client.rs
+++ b/src/transaction/client.rs
@@ -10,7 +10,6 @@ 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;
@@ -44,11 +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<Cod: Codec = ApiV1TxnCodec> {
-    pd: Arc<PdRpcClient<Cod>>,
+pub struct Client {
+    pd: Arc<PdRpcClient>,
 }
 
-impl<Cod: Codec> Clone for Client<Cod> {
+impl Clone for Client {
     fn clone(&self) -> Self {
         Self {
             pd: self.pd.clone(),
@@ -56,7 +55,7 @@ impl<Cod: Codec> Clone for Client<Cod> {
     }
 }
 
-impl Client<ApiV1TxnCodec> {
+impl Client {
     /// 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
@@ -73,6 +72,7 @@ impl Client<ApiV1TxnCodec> {
     /// # });
     /// ```
     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
     }
 
@@ -101,35 +101,9 @@ impl Client<ApiV1TxnCodec> {
         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::<Cod>::connect(&pd_endpoints, config, true, Some(codec)).await?);
+        let pd = Arc::new(PdRpcClient::connect(&pd_endpoints, config, true).await?);
         Ok(Client { pd })
     }
 
@@ -153,7 +127,7 @@ impl<Cod: Codec> Client<Cod> {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_optimistic(&self) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
+    pub async fn begin_optimistic(&self) -> Result<Transaction> {
         debug!("creating new optimistic transaction");
         let timestamp = self.current_timestamp().await?;
         Ok(self.new_transaction(timestamp, TransactionOptions::new_optimistic()))
@@ -176,7 +150,7 @@ impl<Cod: Codec> Client<Cod> {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_pessimistic(&self) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
+    pub async fn begin_pessimistic(&self) -> Result<Transaction> {
         debug!("creating new pessimistic transaction");
         let timestamp = self.current_timestamp().await?;
         Ok(self.new_transaction(timestamp, TransactionOptions::new_pessimistic()))
@@ -199,21 +173,14 @@ impl<Cod: Codec> Client<Cod> {
     /// transaction.commit().await.unwrap();
     /// # });
     /// ```
-    pub async fn begin_with_options(
-        &self,
-        options: TransactionOptions,
-    ) -> Result<Transaction<Cod, PdRpcClient<Cod>>> {
+    pub async fn begin_with_options(&self, options: TransactionOptions) -> Result<Transaction> {
         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<Cod, PdRpcClient<Cod>> {
+    pub fn snapshot(&self, timestamp: Timestamp, options: TransactionOptions) -> Snapshot {
         debug!("creating new snapshot");
         Snapshot::new(self.new_transaction(timestamp, options.read_only()))
     }
@@ -280,8 +247,7 @@ impl<Cod: Codec> Client<Cod> {
         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 encoded_req = EncodedRequest::new(req, self.pd.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.pd.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.pd.clone(), req)
             .cleanup_locks(ctx.clone(), options, backoff)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .extract_error()
@@ -300,8 +266,7 @@ impl<Cod: Codec> Client<Cod> {
         batch_size: u32,
     ) -> Result<Vec<crate::proto::kvrpcpb::LockInfo>> {
         let req = new_scan_lock_request(range.into(), safepoint, batch_size);
-        let encoded_req = EncodedRequest::new(req, self.pd.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.pd.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.pd.clone(), req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .merge(crate::request::Collect)
             .plan();
@@ -317,19 +282,14 @@ impl<Cod: Codec> Client<Cod> {
     /// This interface is intended for special scenarios that resemble operations like "drop table" or "drop database" in TiDB.
     pub async fn unsafe_destroy_range(&self, range: impl Into<BoundRange>) -> Result<()> {
         let req = new_unsafe_destroy_range_request(range.into());
-        let encoded_req = EncodedRequest::new(req, self.pd.get_codec());
-        let plan = crate::request::PlanBuilder::new(self.pd.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(self.pd.clone(), req)
             .all_stores(DEFAULT_STORE_BACKOFF)
             .merge(crate::request::Collect)
             .plan();
         plan.execute().await
     }
 
-    fn new_transaction(
-        &self,
-        timestamp: Timestamp,
-        options: TransactionOptions,
-    ) -> Transaction<Cod, PdRpcClient<Cod>> {
+    fn new_transaction(&self, timestamp: Timestamp, options: TransactionOptions) -> Transaction {
         Transaction::new(timestamp, self.pd.clone(), options)
     }
 }
diff --git a/src/transaction/lock.rs b/src/transaction/lock.rs
index afb1d6c4..8d70d07e 100644
--- a/src/transaction/lock.rs
+++ b/src/transaction/lock.rs
@@ -17,7 +17,6 @@ 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;
@@ -76,8 +75,7 @@ pub async fn resolve_locks(
             Some(&commit_version) => commit_version,
             None => {
                 let request = requests::new_cleanup_request(lock.primary_lock, lock.lock_version);
-                let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
-                let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+                let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
                     .resolve_lock(OPTIMISTIC_BACKOFF)
                     .retry_multi_region(DEFAULT_REGION_BACKOFF)
                     .merge(CollectSingle)
@@ -118,8 +116,8 @@ 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);
-        let encoded_req = EncodedRequest::new(request, pd_client.get_codec());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+        // The only place where single-region is used
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
             .single_region_with_store(store)
             .await?
             .resolve_lock(Backoff::no_backoff())
@@ -359,8 +357,7 @@ impl LockResolver {
             force_sync_commit,
             resolving_pessimistic_lock,
         );
-        let encoded_req = EncodedRequest::new(req, pd_client.get_codec());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .merge(CollectSingle)
             .extract_error()
@@ -384,8 +381,7 @@ impl LockResolver {
         txn_id: u64,
     ) -> Result<SecondaryLocksStatus> {
         let req = new_check_secondary_locks_request(keys, txn_id);
-        let encoded_req = EncodedRequest::new(req, pd_client.get_codec());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), req)
             .retry_multi_region(DEFAULT_REGION_BACKOFF)
             .extract_error()
             .merge(Collect)
@@ -401,8 +397,7 @@ 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 encoded_req = EncodedRequest::new(request, pd_client.get_codec());
-        let plan = crate::request::PlanBuilder::new(pd_client.clone(), encoded_req)
+        let plan = crate::request::PlanBuilder::new(pd_client.clone(), request)
             .single_region_with_store(store.clone())
             .await?
             .extract_error()
diff --git a/src/transaction/requests.rs b/src/transaction/requests.rs
index 4f3e1b93..c08025e0 100644
--- a/src/transaction/requests.rs
+++ b/src/transaction/requests.rs
@@ -39,7 +39,6 @@ use crate::shardable_keys;
 use crate::shardable_range;
 use crate::store::store_stream_for_range;
 use crate::store::RegionStore;
-use crate::store::Request;
 use crate::store::{store_stream_for_keys, Store};
 use crate::timestamp::TimestampExt;
 use crate::transaction::HasLocks;
@@ -298,7 +297,7 @@ impl Shardable for kvrpcpb::PrewriteRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(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) {
@@ -365,7 +364,7 @@ impl Shardable for kvrpcpb::CommitRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         self.keys = shard.into_iter().map(Into::into).collect();
         Ok(())
     }
@@ -456,7 +455,7 @@ impl Shardable for kvrpcpb::PessimisticLockRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         self.mutations = shard;
         Ok(())
     }
@@ -557,7 +556,7 @@ impl Shardable for kvrpcpb::ScanLockRequest {
     }
 
     fn apply_shard(&mut self, shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         self.start_key = shard.0;
         Ok(())
     }
@@ -618,7 +617,7 @@ impl Shardable for kvrpcpb::TxnHeartBeatRequest {
     }
 
     fn apply_shard(&mut self, mut shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(store.region_with_leader.context()?);
         assert!(shard.len() == 1);
         self.primary_lock = shard.pop().unwrap();
         Ok(())
@@ -676,7 +675,7 @@ impl Shardable for kvrpcpb::CheckTxnStatusRequest {
     }
 
     fn apply_shard(&mut self, mut shard: Self::Shard, store: &RegionStore) -> Result<()> {
-        self.set_context(store.region_with_leader.context()?);
+        self.context = Some(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 0d1e4803..5694614b 100644
--- a/src/transaction/snapshot.rs
+++ b/src/transaction/snapshot.rs
@@ -2,11 +2,7 @@
 
 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;
@@ -22,12 +18,11 @@ use crate::Value;
 ///
 /// See the [Transaction](struct@crate::Transaction) docs for more information on the methods.
 #[derive(new)]
-pub struct Snapshot<Cod: Codec = ApiV1TxnCodec, PdC: PdClient<Codec = Cod> = PdRpcClient<Cod>> {
-    transaction: Transaction<Cod, PdC>,
-    phantom: PhantomData<Cod>,
+pub struct Snapshot {
+    transaction: Transaction,
 }
 
-impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Snapshot<Cod, PdC> {
+impl Snapshot {
     /// 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 e984f153..e0f79170 100644
--- a/src/transaction/transaction.rs
+++ b/src/transaction/transaction.rs
@@ -1,7 +1,6 @@
 // Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.
 
 use std::iter;
-use std::marker::PhantomData;
 use std::sync::atomic;
 use std::sync::atomic::AtomicU8;
 use std::sync::Arc;
@@ -16,12 +15,10 @@ 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;
@@ -77,7 +74,7 @@ use crate::Value;
 /// txn.commit().await.unwrap();
 /// # });
 /// ```
-pub struct Transaction<Cod: Codec = ApiV1TxnCodec, PdC: PdClient<Codec = Cod> = PdRpcClient<Cod>> {
+pub struct Transaction<PdC: PdClient = PdRpcClient> {
     status: Arc<AtomicU8>,
     timestamp: Timestamp,
     buffer: Buffer,
@@ -85,15 +82,14 @@ pub struct Transaction<Cod: Codec = ApiV1TxnCodec, PdC: PdClient<Codec = Cod> =
     options: TransactionOptions,
     is_heartbeat_started: bool,
     start_instant: Instant,
-    phantom: PhantomData<Cod>,
 }
 
-impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
+impl<PdC: PdClient> Transaction<PdC> {
     pub(crate) fn new(
         timestamp: Timestamp,
         rpc: Arc<PdC>,
         options: TransactionOptions,
-    ) -> Transaction<Cod, PdC> {
+    ) -> Transaction<PdC> {
         let status = if options.read_only {
             TransactionStatus::ReadOnly
         } else {
@@ -107,7 +103,6 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
             options,
             is_heartbeat_started: false,
             start_instant: std::time::Instant::now(),
-            phantom: PhantomData,
         }
     }
 
@@ -140,8 +135,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
         self.buffer
             .get_or_else(key, |key| async move {
                 let request = new_get_request(key, timestamp);
-                let encoded_req = EncodedRequest::new(request, rpc.get_codec());
-                let plan = PlanBuilder::new(rpc, encoded_req)
+                let plan = PlanBuilder::new(rpc, request)
                     .resolve_lock(retry_options.lock_backoff)
                     .retry_multi_region(DEFAULT_REGION_BACKOFF)
                     .merge(CollectSingle)
@@ -271,8 +265,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, 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 encoded_req = EncodedRequest::new(request, rpc.get_codec());
-                let plan = PlanBuilder::new(rpc, encoded_req)
+                let plan = PlanBuilder::new(rpc, request)
                     .resolve_lock(retry_options.lock_backoff)
                     .retry_multi_region(retry_options.region_backoff)
                     .merge(Collect)
@@ -745,8 +738,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
             primary_key,
             self.start_instant.elapsed().as_millis() as u64 + MAX_TTL,
         );
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = PlanBuilder::new(self.rpc.clone(), request)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .merge(CollectSingle)
@@ -776,8 +768,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
                 move |new_range, new_limit| async move {
                     let request =
                         new_scan_request(new_range, timestamp, new_limit, key_only, reverse);
-                    let encoded_req = EncodedRequest::new(request, rpc.get_codec());
-                    let plan = PlanBuilder::new(rpc, encoded_req)
+                    let plan = PlanBuilder::new(rpc, request)
                         .resolve_lock(retry_options.lock_backoff)
                         .retry_multi_region(retry_options.region_backoff)
                         .merge(Collect)
@@ -832,8 +823,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
             for_update_ts.clone(),
             need_value,
         );
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = PlanBuilder::new(self.rpc.clone(), request)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .preserve_shard()
             .retry_multi_region_preserve_results(self.options.retry_options.region_backoff.clone())
@@ -887,8 +877,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
             start_version,
             for_update_ts,
         );
-        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = PlanBuilder::new(self.rpc.clone(), req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .extract_error()
@@ -957,8 +946,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
                     primary_key.clone(),
                     start_instant.elapsed().as_millis() as u64 + MAX_TTL,
                 );
-                let encoded_req = EncodedRequest::new(request, rpc.get_codec());
-                let plan = PlanBuilder::new(rpc.clone(), encoded_req)
+                let plan = PlanBuilder::new(rpc.clone(), request)
                     .retry_multi_region(region_backoff.clone())
                     .merge(CollectSingle)
                     .plan();
@@ -1005,7 +993,7 @@ impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Transaction<Cod, PdC> {
     }
 }
 
-impl<Cod: Codec, PdC: PdClient<Codec = Cod>> Drop for Transaction<Cod, PdC> {
+impl<PdC: PdClient> Drop for Transaction<PdC> {
     fn drop(&mut self) {
         debug!("dropping transaction");
         if std::thread::panicking() {
@@ -1296,8 +1284,7 @@ impl<PdC: PdClient> Committer<PdC> {
             .collect();
         // FIXME set max_commit_ts and min_commit_ts
 
-        let encoded_req = EncodedRequest::new(request, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = PlanBuilder::new(self.rpc.clone(), request)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .merge(CollectError)
@@ -1337,8 +1324,7 @@ impl<PdC: PdClient> Committer<PdC> {
             self.start_version.clone(),
             commit_version.clone(),
         );
-        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc.clone(), encoded_req)
+        let plan = PlanBuilder::new(self.rpc.clone(), req)
             .resolve_lock(self.options.retry_options.lock_backoff.clone())
             .retry_multi_region(self.options.retry_options.region_backoff.clone())
             .extract_error()
@@ -1402,8 +1388,7 @@ impl<PdC: PdClient> Committer<PdC> {
                 .filter(|key| &primary_key != key);
             new_commit_request(keys, self.start_version, commit_version)
         };
-        let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-        let plan = PlanBuilder::new(self.rpc, encoded_req)
+        let plan = PlanBuilder::new(self.rpc, req)
             .resolve_lock(self.options.retry_options.lock_backoff)
             .retry_multi_region(self.options.retry_options.region_backoff)
             .extract_error()
@@ -1424,8 +1409,7 @@ impl<PdC: PdClient> Committer<PdC> {
         match self.options.kind {
             TransactionKind::Optimistic => {
                 let req = new_batch_rollback_request(keys, self.start_version);
-                let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-                let plan = PlanBuilder::new(self.rpc, encoded_req)
+                let plan = PlanBuilder::new(self.rpc, req)
                     .resolve_lock(self.options.retry_options.lock_backoff)
                     .retry_multi_region(self.options.retry_options.region_backoff)
                     .extract_error()
@@ -1434,8 +1418,7 @@ impl<PdC: PdClient> Committer<PdC> {
             }
             TransactionKind::Pessimistic(for_update_ts) => {
                 let req = new_pessimistic_rollback_request(keys, self.start_version, for_update_ts);
-                let encoded_req = EncodedRequest::new(req, self.rpc.get_codec());
-                let plan = PlanBuilder::new(self.rpc, encoded_req)
+                let plan = PlanBuilder::new(self.rpc, req)
                     .resolve_lock(self.options.retry_options.lock_backoff)
                     .retry_multi_region(self.options.retry_options.region_backoff)
                     .extract_error()