feat(remote_wal): add skeleton for remote wal related to datanode (#2941)

* refactor: refactor wal config

* test: update tests related to wal

* feat: introduce kafka wal config

* chore: augment proto with wal options

* feat: augment region open request with wal options

* feat: augment mito region with wal options

* feat: augment region create request with wal options

* refactor: refactor log store trait

* feat: add skeleton for kafka log store

* feat: generalize building log store when starting datanode

* feat: integrate wal options to region write

* chore: minor update

* refactor: remove wal options from region create/open requests

* fix: compliation issues

* chore: insert wal options into region options upon initializing region server

* chore: integrate wal options into region options

* chore: fill in kafka wal config

* chore: reuse namespaces while writing to wal

* chore: minor update

* chore: fetch wal options from region while handling truncate/flush

* fix: region options test

* fix: resolve some review conversations

* refactor: serde with wal options

* fix: resolve some review conversations

config/datanode.example.toml

@@ -29,9 +29,15 @@ connect_timeout = "1s"
 # `TCP_NODELAY` option for accepted connections, true by default.
 tcp_nodelay = true
 
-# WAL options, see `standalone.example.toml`.
+# WAL options.
+# Currently, users are expected to choose the wal through the provider field. 
+# When a wal provider is chose, the user should comment out all other wal config 
+# except those corresponding to the chosen one.
 [wal]
 # WAL data directory
+provider = "raft_engine"
+
+# Raft-engine wal options, see `standalone.example.toml`
 # dir = "/tmp/greptimedb/wal"
 file_size = "256MB"
 purge_threshold = "4GB"
@@ -39,6 +45,22 @@ purge_interval = "10m"
 read_batch_size = 128
 sync_write = false
 
+# Kafka wal options.
+# The broker endpoints of the Kafka cluster. ["127.0.0.1:9090"] by default.
+# broker_endpoints = ["127.0.0.1:9090"]
+# Number of topics shall be created beforehand.
+# num_topics = 64
+# Topic name prefix.
+# topic_name_prefix = "greptimedb_wal_kafka_topic"
+# Number of partitions per topic.
+# num_partitions = 1
+# The maximum log size an rskafka batch producer could buffer.
+# max_batch_size = "4MB"
+# The linger duration of an rskafka batch producer.
+# linger = "200ms"
+# The maximum amount of time (in milliseconds) to wait for Kafka records to be returned.
+# max_wait_time = "100ms"
+
 # Storage options, see `standalone.example.toml`.
 [storage]
 # The working home directory.

config/standalone.example.toml

@@ -82,6 +82,13 @@ enable = true
 
 # WAL options.
 [wal]
+# Available wal providers:
+# - "RaftEngine" (default)
+# - "Kafka"
+provider = "raft_engine"
+
+# There's no kafka wal config for standalone mode.
+
 # WAL data directory
 # dir = "/tmp/greptimedb/wal"
 # WAL file size in bytes.