diff --git a/Cargo.lock b/Cargo.lock
index 6e3d775..d28b699 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -713,6 +713,15 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "284f18f85651fe11e8a991b2adb42cb078325c996ed026d994719efcfca1d54b"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "0.4.6"
@@ -898,6 +907,7 @@ dependencies = [
  "derive-new",
  "futures 0.3.5",
  "grpcio",
+ "itertools 0.9.0",
  "kvproto",
  "log",
  "tikv-client-common",
@@ -1222,7 +1232,7 @@ checksum = "02b10678c913ecbd69350e8535c3aef91a8676c0773fc1d7b95cdd196d7f2f26"
 dependencies = [
  "bytes",
  "heck",
- "itertools",
+ "itertools 0.8.2",
  "log",
  "multimap",
  "petgraph",
@@ -1239,7 +1249,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "537aa19b95acde10a12fec4301466386f757403de4cd4e5b4fa78fb5ecb18f72"
 dependencies = [
  "anyhow",
- "itertools",
+ "itertools 0.8.2",
  "proc-macro2 1.0.19",
  "quote 1.0.7",
  "syn 1.0.35",
diff --git a/mock-tikv/Cargo.toml b/mock-tikv/Cargo.toml
index fa81f51..92b024c 100644
--- a/mock-tikv/Cargo.toml
+++ b/mock-tikv/Cargo.toml
@@ -10,3 +10,4 @@ kvproto = { git = "https://github.com/pingcap/kvproto.git", rev = "1e28226154c37
 derive-new = "0.5.8"
 tikv-client-common = { path = "../tikv-client-common"}
 log = "0.4"
+itertools = "0.9.0"
diff --git a/mock-tikv/src/lib.rs b/mock-tikv/src/lib.rs
index cf43679..8eee772 100644
--- a/mock-tikv/src/lib.rs
+++ b/mock-tikv/src/lib.rs
@@ -7,6 +7,8 @@ pub use pd::{start_mock_pd_server, MockPd, MOCK_PD_PORT};
 pub use server::{start_mock_tikv_server, MockTikv, MOCK_TIKV_PORT};
 pub use store::KvStore;
 
+/// A common pattern for implementing an unary RPC call.
+/// Successfully returns the result.
 #[macro_export]
 macro_rules! spawn_unary_success {
     ($ctx:ident, $req:ident, $resp:ident, $sink:ident) => {
diff --git a/mock-tikv/src/pd.rs b/mock-tikv/src/pd.rs
index d8b88d0..82dbcce 100644
--- a/mock-tikv/src/pd.rs
+++ b/mock-tikv/src/pd.rs
@@ -19,12 +19,12 @@ impl MockPd {
     }
 
     fn region() -> kvproto::metapb::Region {
-        let mut meta_region = kvproto::metapb::Region::default();
-        meta_region.set_end_key(vec![0xff; 20]);
-        meta_region.set_start_key(vec![0x00]);
-        meta_region.set_id(0);
-        meta_region.set_peers(vec![Self::leader()]);
-        meta_region
+        kvproto::metapb::Region {
+            start_key: vec![],
+            end_key: vec![],
+            peers: vec![Self::leader()],
+            ..Default::default()
+        }
     }
 
     fn leader() -> kvproto::metapb::Peer {
@@ -32,10 +32,11 @@ impl MockPd {
     }
 
     fn store() -> kvproto::metapb::Store {
-        let mut store = kvproto::metapb::Store::default();
-        store.set_address(format!("localhost:{}", MOCK_TIKV_PORT));
         // TODO: start_timestamp?
-        store
+        kvproto::metapb::Store {
+            address: format!("localhost:{}", MOCK_TIKV_PORT),
+            ..Default::default()
+        }
     }
 }
 
@@ -57,15 +58,16 @@ impl Pd for MockPd {
         req: GetMembersRequest,
         sink: ::grpcio::UnarySink<GetMembersResponse>,
     ) {
-        let mut resp = GetMembersResponse::default();
-        resp.set_header(ResponseHeader::default());
-        let mut member = Member::default();
-        member.set_name("mock tikv".to_owned());
-        member.set_member_id(0);
-        member.set_client_urls(vec![format!("localhost:{}", MOCK_PD_PORT)]);
-        // member.set_peer_urls(vec![format!("localhost:{}", MOCK_PD_PORT)]);
-        resp.set_members(vec![member.clone()]);
-        resp.set_leader(member);
+        let member = Member {
+            name: "mock tikv".to_owned(),
+            client_urls: vec![format!("localhost:{}", MOCK_PD_PORT)],
+            ..Default::default()
+        };
+        let resp = GetMembersResponse {
+            members: vec![member.clone()],
+            leader: Some(member),
+            ..Default::default()
+        };
         spawn_unary_success!(ctx, req, resp, sink);
     }
 
@@ -77,9 +79,8 @@ impl Pd for MockPd {
     ) {
         let f = stream
             .map(|_| {
-                let mut resp = TsoResponse::default();
+                let resp = TsoResponse::default();
                 // TODO: make ts monotonic
-                resp.set_timestamp(Timestamp::default());
                 Ok((resp, WriteFlags::default()))
             })
             .forward(sink)
@@ -120,8 +121,10 @@ impl Pd for MockPd {
         req: GetStoreRequest,
         sink: ::grpcio::UnarySink<GetStoreResponse>,
     ) {
-        let mut resp = GetStoreResponse::default();
-        resp.set_store(Self::store());
+        let resp = GetStoreResponse {
+            store: Some(Self::store()),
+            ..Default::default()
+        };
         spawn_unary_success!(ctx, req, resp, sink);
     }
 
@@ -167,9 +170,11 @@ impl Pd for MockPd {
         req: GetRegionRequest,
         sink: ::grpcio::UnarySink<GetRegionResponse>,
     ) {
-        let mut resp = GetRegionResponse::default();
-        resp.set_region(Self::region());
-        resp.set_leader(Self::leader());
+        let resp = GetRegionResponse {
+            region: Some(Self::region()),
+            leader: Some(Self::leader()),
+            ..Default::default()
+        };
         spawn_unary_success!(ctx, req, resp, sink);
     }
 
@@ -188,9 +193,11 @@ impl Pd for MockPd {
         req: GetRegionByIdRequest,
         sink: ::grpcio::UnarySink<GetRegionResponse>,
     ) {
-        let mut resp = GetRegionResponse::default();
-        resp.set_region(Self::region());
-        resp.set_leader(Self::leader());
+        let resp = GetRegionResponse {
+            region: Some(Self::region()),
+            leader: Some(Self::leader()),
+            ..Default::default()
+        };
         spawn_unary_success!(ctx, req, resp, sink);
     }
 
diff --git a/mock-tikv/src/server.rs b/mock-tikv/src/server.rs
index 268646d..abacbf5 100644
--- a/mock-tikv/src/server.rs
+++ b/mock-tikv/src/server.rs
@@ -4,6 +4,7 @@ use crate::{spawn_unary_success, KvStore};
 use derive_new::new;
 use futures::{FutureExt, TryFutureExt};
 use grpcio::{Environment, Server, ServerBuilder};
+use itertools::Itertools;
 use kvproto::{kvrpcpb::*, tikvpb::*};
 use std::sync::Arc;
 
@@ -198,7 +199,8 @@ impl Tikv for MockTikv {
         req: kvproto::kvrpcpb::RawPutRequest,
         sink: grpcio::UnarySink<kvproto::kvrpcpb::RawPutResponse>,
     ) {
-        self.inner.raw_put(req.get_key(), req.get_value());
+        self.inner
+            .raw_put(req.get_key().to_vec(), req.get_value().to_vec());
         let resp = RawPutResponse::default();
         spawn_unary_success!(ctx, req, resp, sink);
     }
@@ -224,7 +226,7 @@ impl Tikv for MockTikv {
         let key = req.get_key();
         let res = self.inner.raw_delete(key);
         let mut resp = RawDeleteResponse::default();
-        if res.is_err() {
+        if res.is_none() {
             resp.set_error("Key not exist".to_owned());
         }
         spawn_unary_success!(ctx, req, resp, sink);
@@ -242,7 +244,11 @@ impl Tikv for MockTikv {
         if res.is_err() {
             resp.set_error(format!(
                 "Non-existent keys:[{}]",
-                res.err().unwrap().join(", ")
+                res.err()
+                    .unwrap()
+                    .iter()
+                    .map(|k| std::str::from_utf8(k).unwrap())
+                    .join(", ")
             ));
         }
         spawn_unary_success!(ctx, req, resp, sink);
diff --git a/mock-tikv/src/store.rs b/mock-tikv/src/store.rs
index a7ffbed..5226d2c 100644
--- a/mock-tikv/src/store.rs
+++ b/mock-tikv/src/store.rs
@@ -26,7 +26,7 @@ impl KvStore {
 
     pub fn raw_get(&self, key: &[u8]) -> Vec<u8> {
         let data = self.data.read().unwrap();
-        data.get(key).unwrap_or(&vec![]).to_vec()
+        data.get(key).map(|v| v.to_vec()).unwrap_or_else(Vec::new)
     }
 
     pub fn raw_batch_get(&self, keys: &[Vec<u8>]) -> Vec<KvPair> {
@@ -34,38 +34,37 @@ impl KvStore {
         keys.iter()
             .map(|key| {
                 let mut pair = KvPair::default();
-                pair.set_value(data.get(key).unwrap_or(&vec![]).to_vec());
+                pair.set_value(data.get(key).map(|v| v.to_vec()).unwrap_or_else(Vec::new));
                 pair.set_key(key.to_vec());
                 pair
             })
-            .collect::<Vec<_>>()
+            .collect()
     }
 
-    pub fn raw_put(&self, key: &[u8], value: &[u8]) {
+    pub fn raw_put(&self, key: Vec<u8>, value: Vec<u8>) {
         let mut data = self.data.write().unwrap();
-        *data.entry(key.to_vec()).or_default() = value.to_vec();
+        data.insert(key, value);
     }
 
     pub fn raw_batch_put(&self, pairs: &[KvPair]) {
         let mut data = self.data.write().unwrap();
         for pair in pairs {
-            *data.entry(pair.get_key().to_vec()).or_default() = pair.get_value().to_vec();
+            data.insert(pair.get_key().to_vec(), pair.get_value().to_vec());
         }
     }
 
     // if success, return the key deleted
-    pub fn raw_delete(&self, key: &[u8]) -> Result<Vec<u8>, ()> {
+    pub fn raw_delete(&self, key: &[u8]) -> Option<Vec<u8>> {
         let mut data = self.data.write().unwrap();
-        data.remove(key).ok_or(())
+        data.remove(key)
     }
 
     // if any of the key does not exist, return non-existent keys
-    pub fn raw_batch_delete<'a>(&self, keys: &'a [Vec<u8>]) -> Result<(), Vec<&'a str>> {
+    pub fn raw_batch_delete<'a>(&self, keys: &'a [Vec<u8>]) -> Result<(), Vec<&'a Vec<u8>>> {
         let mut data = self.data.write().unwrap();
         let non_exist_keys = keys
             .iter()
             .filter(|&key| !data.contains_key(key))
-            .map(|key| std::str::from_utf8(key).unwrap())
             .collect::<Vec<_>>();
         if !non_exist_keys.is_empty() {
             Err(non_exist_keys)
diff --git a/src/raw/mod.rs b/src/raw/mod.rs
index b1fb530..7aea986 100644
--- a/src/raw/mod.rs
+++ b/src/raw/mod.rs
@@ -16,7 +16,7 @@ use std::{convert::TryFrom, fmt};
 use tikv_client_common::errors::ErrorKind::ColumnFamilyError;
 
 mod client;
-pub(crate) mod requests;
+mod requests;
 
 /// A [`ColumnFamily`](ColumnFamily) is an optional parameter for [`raw::Client`](Client) requests.
 ///