chore: fill in kafka config

config/metasrv.example.toml

@@ -44,4 +44,25 @@ first_heartbeat_estimate = "1000ms"
 # tcp_nodelay = true
 
 [wal]
+# Available wal providers:
+# - "raft-engine" (default)
+# - "kafka"
 provider = "raft-engine"
+
+# There're none raft-engine wal config since meta srv only involves in remote wal currently.
+
+# 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

src/common/meta/src/wal/kafka.rs

@@ -19,13 +19,40 @@ mod topic_selector;
 use serde::{Deserialize, Serialize};
 
 use crate::wal::kafka::topic::Topic;
+use crate::wal::kafka::topic_selector::SelectorType as TopicSelectorType;
 
 /// Configurations for bootstraping a kafka wal.
-#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Default)]
-pub struct KafkaConfig;
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct KafkaConfig {
+    /// The broker endpoints of the Kafka cluster.
+    pub broker_endpoints: Vec<String>,
+    /// Number of topics to be created upon start.
+    pub num_topics: usize,
+    /// The type of the topic selector with which to select a topic for a region.
+    pub selector_type: TopicSelectorType,
+    /// Topic name prefix.
+    pub topic_name_prefix: String,
+    /// Number of partitions per topic.
+    pub num_partitions: i32,
+    /// The replication factor of each topic.
+    pub replication_factor: i16,
+}
+
+impl Default for KafkaConfig {
+    fn default() -> Self {
+        Self {
+            broker_endpoints: vec!["127.0.0.1:9090".to_string()],
+            num_topics: 64,
+            selector_type: TopicSelectorType::RoundRobin,
+            topic_name_prefix: "greptimedb_wal".to_string(),
+            num_partitions: 1,
+            replication_factor: 3,
+        }
+    }
+}
 
 /// Kafka wal options allocated to a region.
-#[derive(Serialize, Deserialize, Default, Debug, Clone, PartialEq)]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 pub struct KafkaWalOptions {
     /// Kafka wal topic.
     /// Publishers publish log entries to the topic while subscribers pull log entries from the topic.

src/common/meta/src/wal/kafka/topic_selector.rs

@@ -12,12 +12,17 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::default;
 use std::sync::Arc;
 
+use serde::{Deserialize, Serialize};
+
 use crate::wal::kafka::topic::Topic;
 
 /// The type of the topic selector, i.e. with which strategy to select a topic.
-pub(super) enum SelectorType {
+#[derive(Default, Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub enum SelectorType {
+    #[default]
     RoundRobin,
 }