Update metricstore documentation

Entire-Checkpoint: 99f20c1edd90

pkg/metricstore/archive.go

@@ -3,6 +3,12 @@
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
 
+// This file implements the cleanup (archiving or deletion) of old checkpoint files.
+//
+// The CleanUp worker runs on a timer equal to RetentionInMemory. In "archive" mode
+// it converts checkpoint files older than the retention window into per-cluster
+// Parquet files and then deletes the originals. In "delete" mode it simply removes
+// old checkpoint files.
 package metricstore
 
 import (
@@ -19,8 +25,12 @@ import (
 	cclog "github.com/ClusterCockpit/cc-lib/v2/ccLogger"
 )
 
-// Worker for either Archiving or Deleting files
+// CleanUp starts a background worker that periodically removes or archives
-
+// checkpoint files older than the configured retention window.
+//
+// In "archive" mode, old checkpoint files are converted to Parquet and stored
+// under Keys.Cleanup.RootDir. In "delete" mode they are simply removed.
+// The cleanup interval equals Keys.RetentionInMemory.
 func CleanUp(wg *sync.WaitGroup, ctx context.Context) {
 	if Keys.Cleanup.Mode == "archive" {
 		cclog.Info("[METRICSTORE]> enable archive cleanup to parquet")

pkg/metricstore/checkpoint.go

@@ -86,11 +86,12 @@ var (
 
 // Checkpointing starts a background worker that periodically saves metric data to disk.
 //
-// Checkpoints are written every 12 hours (hardcoded).
+// The checkpoint interval is read from Keys.CheckpointInterval (default: 12 hours).
 //
 // Format behaviour:
-//   - "json": Periodic checkpointing every checkpointInterval
+//   - "json": Writes a JSON snapshot file per host every interval
-//   - "wal":  Periodic binary snapshots + WAL rotation every checkpointInterval
+//   - "wal":  Writes a binary snapshot file per host every interval, then rotates
+//     the current.wal files for all successfully checkpointed hosts
 func Checkpointing(wg *sync.WaitGroup, ctx context.Context) {
 	lastCheckpointMu.Lock()
 	lastCheckpoint = time.Now()

pkg/metricstore/metricstore.go

@@ -8,7 +8,7 @@
 //
 // The package organizes metrics in a tree structure (cluster → host → component) and
 // provides concurrent read/write access to metric data with configurable aggregation strategies.
-// Background goroutines handle periodic checkpointing (JSON or Avro format), archiving old data,
+// Background goroutines handle periodic checkpointing (JSON or WAL/binary format), archiving old data,
 // and enforcing retention policies.
 //
 // Key features:
@@ -16,7 +16,7 @@
 //   - Hierarchical data organization (selectors)
 //   - Concurrent checkpoint/archive workers
 //   - Support for sum and average aggregation
-//   - NATS integration for metric ingestion
+//   - NATS integration for metric ingestion via InfluxDB line protocol
 package metricstore
 
 import (
@@ -113,7 +113,8 @@ type MemoryStore struct {
 //  6. Optionally subscribes to NATS for real-time metric ingestion
 //
 // Parameters:
-//   - rawConfig: JSON configuration for the metric store (see MetricStoreConfig)
+//   - rawConfig: JSON configuration for the metric store (see MetricStoreConfig); may be nil to use defaults
+//   - metrics: Map of metric names to their configurations (frequency and aggregation strategy)
 //   - wg: WaitGroup that will be incremented for each background goroutine started
 //
 // The function will call cclog.Fatal on critical errors during initialization.

pkg/metricstore/walCheckpoint.go

@@ -400,8 +400,9 @@ func walShardIndexFromDir(hostDir string) int {
 	return walShardIndex(cluster, node)
 }
 
-// RotateWALFiles sends rotation requests for the given host directories
+// RotateWALFilesAfterShutdown directly removes current.wal files for the given
-// and blocks until all rotations complete.
+// host directories. Used after shutdown, when WALStaging goroutines have already
+// exited and the channel-based RotateWALFiles is no longer safe to call.
 func RotateWALFilesAfterShutdown(hostDirs []string) {
 	for _, dir := range hostDirs {
 		walPath := path.Join(dir, "current.wal")