Add doc-comments for new metadata sub-modules

scylla/src/cluster/metadata/fetching.rs

@@ -1,3 +1,19 @@
+//! Metadata fetching and processing module.
+//!
+//! This module is responsible for querying cluster metadata from the control connection,
+//! including information about peers (nodes in the cluster), keyspaces, tables, views,
+//! and user-defined types (UDTs).
+//!
+//! The main entry point is [`ControlConnection::query_metadata`], which fetches all
+//! metadata needed to maintain an up-to-date view of the cluster topology and schema.
+//!
+//! Key functionality includes:
+//! - Querying peer information from `system.peers` and `system.local` tables
+//! - Fetching keyspace metadata including replication strategies
+//! - Loading table and materialized view schemas from `system_schema` tables
+//! - Processing user-defined types with proper dependency resolution via topological sort
+//! - Parsing CQL type strings into structured type representations
+
 use std::borrow::BorrowMut;
 use std::cell::Cell;
 use std::collections::HashMap;

scylla/src/cluster/metadata/reader.rs

@@ -1,3 +1,18 @@
+//! This module contains the [`MetadataReader`] struct, which is responsible for
+//! fetching and maintaining cluster metadata through a control connection.
+//!
+//! The control connection is a dedicated connection to one of the cluster nodes
+//! that is used to:
+//! - Fetch cluster metadata (topology, schema, token ring information)
+//! - Receive server-side events (topology changes, schema changes, status changes)
+//!
+//! [`MetadataReader`] handles control connection lifecycle, including:
+//! - Initial connection establishment to contact points
+//! - Automatic reconnection to other known peers on connection failure
+//! - Fallback to initial contact points when all known peers are unreachable
+//! - Host filtering to ensure the control connection is established to an accepted node
+//!
+
 use std::sync::Arc;
 use std::time::Duration;