fix: add serde default to MitoConfig (#2650)

* fix: add serde default to MitoConfig

* docs: update config toml

config/datanode.example.toml

@@ -101,6 +101,10 @@ auto_flush_interval = "1h"
 global_write_buffer_size = "1GB"
 # Global write buffer size threshold to reject write requests (default 2G).
 global_write_buffer_reject_size = "2GB"
+# Cache size for SST metadata (default 128MB). Setting it to 0 to disable the cache.
+sst_meta_cache_size = "128MB"
+# Cache size for vectors and arrow arrays (default 512MB). Setting it to 0 to disable the cache.
+vector_cache_size = "512MB"
 
 # Log options
 # [logging]

src/mito2/src/config.rs

@@ -28,6 +28,7 @@ const DEFAULT_MAX_BG_JOB: usize = 4;
 
 /// Configuration for [MitoEngine](crate::engine::MitoEngine).
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
+#[serde(default)]
 pub struct MitoConfig {
     // Worker configs:
     /// Number of region workers (default 1).