diff --git a/config/metasrv.example.toml b/config/metasrv.example.toml
index abb2e42ec081..704dd90784a0 100644
--- a/config/metasrv.example.toml
+++ b/config/metasrv.example.toml
@@ -51,18 +51,19 @@ provider = "raft_engine"
 
 # There're none raft-engine wal config since meta srv only involves in remote wal currently.
 
+# Uncomment the following lines if switching provider to "kafka".
 # Kafka wal config.
 # The broker endpoints of the Kafka cluster. ["127.0.0.1:9090"] by default.
-broker_endpoints = ["127.0.0.1:9090"]
-# Number of topics to be created upon start.
-num_topics = 64
-# Topic selector type.
-# Available selector types: 
-# - "round_robin" (default)
-selector_type = "round_robin"
-# A Kafka topic is constructed by concatenating `topic_name_prefix` and `topic_id`.
-topic_name_prefix = "greptimedb_kafka_wal"
-# Number of partitions per topic.
-num_partitions = 1
-# Expected number of replicas of each partition.
-replication_factor = 3
+# broker_endpoints = ["127.0.0.1:9090"]
+# # Number of topics to be created upon start.
+# num_topics = 64
+# # Topic selector type.
+# # Available selector types: 
+# # - "round_robin" (default)
+# selector_type = "round_robin"
+# # A Kafka topic is constructed by concatenating `topic_name_prefix` and `topic_id`.
+# topic_name_prefix = "greptimedb_kafka_wal"
+# # Number of partitions per topic.
+# num_partitions = 1
+# # Expected number of replicas of each partition.
+# replication_factor = 3
diff --git a/src/cmd/src/cli/bench/metadata.rs b/src/cmd/src/cli/bench/metadata.rs
index fa1b88a76664..4298798e9733 100644
--- a/src/cmd/src/cli/bench/metadata.rs
+++ b/src/cmd/src/cli/bench/metadata.rs
@@ -17,9 +17,7 @@ use std::time::Instant;
 use common_meta::key::TableMetadataManagerRef;
 use common_meta::table_name::TableName;
 
-use super::{
-    bench_self_recorded, create_region_routes, create_region_wal_options, create_table_info,
-};
+use crate::cli::bench::*;
 
 pub struct TableMetadataBencher {
     table_metadata_manager: TableMetadataManagerRef,
diff --git a/src/common/meta/src/key/datanode_table.rs b/src/common/meta/src/key/datanode_table.rs
index 431b0c20c0e5..bf2428deb3c4 100644
--- a/src/common/meta/src/key/datanode_table.rs
+++ b/src/common/meta/src/key/datanode_table.rs
@@ -303,7 +303,7 @@ mod tests {
     }
 
     // This test intends to ensure both the `serde_json::to_string` + `serde_json::from_str`
-    // and `serde_json::to_vec` + `serde_json::from_slice` works for `DatanodeTableValue`.
+    // and `serde_json::to_vec` + `serde_json::from_slice` work for `DatanodeTableValue`.
     // Warning: if the key of `region_wal_options` is of type non-String, this test would fail.
     #[test]
     fn test_serde_with_region_info() {
diff --git a/src/common/meta/src/wal.rs b/src/common/meta/src/wal.rs
index a881d7c77889..8e7d550bc07c 100644
--- a/src/common/meta/src/wal.rs
+++ b/src/common/meta/src/wal.rs
@@ -25,8 +25,8 @@ use crate::wal::kafka::KafkaConfig;
 pub use crate::wal::kafka::{KafkaOptions as KafkaWalOptions, Topic as KafkaWalTopic};
 pub use crate::wal::options_allocator::WalOptionsAllocator;
 
-// An encoded wal options will be wrapped into a (WAL_OPTIONS_KEY, encoded wal options) key-value pair
-// and inserted into the options of a `RegionCreateRequest`.
+/// An encoded wal options will be wrapped into a (WAL_OPTIONS_KEY, encoded wal options) key-value pair
+/// and inserted into the options of a `RegionCreateRequest`.
 pub const WAL_OPTIONS_KEY: &str = "wal_options";
 
 /// Wal configurations for bootstrapping meta srv.
@@ -41,9 +41,9 @@ pub enum WalConfig {
 }
 
 /// Wal options allocated to a region.
-// A wal options is encoded by meta srv into a `String` with `serde_json::to_string`.
-// It's then decoded by datanode to a `HashMap<String, String>` with `serde_json::from_str`.
-// Such a encoding/decoding scheme is inspired by the encoding/decoding of `RegionOptions`.
+/// A wal options is encoded by meta srv into a `String` with `serde_json::to_string`.
+/// It's then decoded by datanode to a `HashMap<String, String>` with `serde_json::from_str`.
+/// Such a encoding/decoding scheme is inspired by the encoding/decoding of `RegionOptions`.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
 #[serde(tag = "wal.provider")]
 pub enum WalOptions {
diff --git a/src/common/meta/src/wal/kafka.rs b/src/common/meta/src/wal/kafka.rs
index 189a4190ae9b..b24d14453186 100644
--- a/src/common/meta/src/wal/kafka.rs
+++ b/src/common/meta/src/wal/kafka.rs
@@ -54,17 +54,7 @@ impl Default for KafkaConfig {
 
 /// Kafka wal options allocated to a region.
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
-#[serde(default)]
 pub struct KafkaOptions {
     /// Kafka wal topic.
     pub topic: Topic,
 }
-
-impl Default for KafkaOptions {
-    fn default() -> Self {
-        Self {
-            // To indicates a default deserialized topic is invalid.
-            topic: "invalid_topic".to_string(),
-        }
-    }
-}
diff --git a/src/common/meta/src/wal/kafka/topic.rs b/src/common/meta/src/wal/kafka/topic.rs
index 76d7c0c98b69..67223637f1ae 100644
--- a/src/common/meta/src/wal/kafka/topic.rs
+++ b/src/common/meta/src/wal/kafka/topic.rs
@@ -14,5 +14,5 @@
 
 /// Kafka wal topic.
 /// Publishers publish log entries to the topic while subscribers pull log entries from the topic.
-// A topic is simply a string right now. But it may be more complex in the future.
+/// A topic is simply a string right now. But it may be more complex in the future.
 pub type Topic = String;
diff --git a/src/common/meta/src/wal/kafka/topic_selector.rs b/src/common/meta/src/wal/kafka/topic_selector.rs
index f29ac55b6ba8..169edc6e70b5 100644
--- a/src/common/meta/src/wal/kafka/topic_selector.rs
+++ b/src/common/meta/src/wal/kafka/topic_selector.rs
@@ -20,9 +20,9 @@ use crate::wal::kafka::topic::Topic;
 
 /// The type of the topic selector, i.e. with which strategy to select a topic.
 #[derive(Default, Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "snake_case")]
 pub enum SelectorType {
     #[default]
-    #[serde(rename = "round_robin")]
     RoundRobin,
 }