Verified feat: improve Snapshot func for atomic update using rename

1 files changed, 41 insertions, 0 deletions

diff --git a/state/pebble_backend.go b/state/pebble_backend.go
index b510f8f..f1aae0c 100644
--- a/state/pebble_backend.go
+++ b/state/pebble_backend.go
@@ -4,6 +4,8 @@ import (
         "context"
         "encoding/binary"
         "fmt"
+        "os"
+        "path/filepath"
         "sync"
 
         "flux/core"
@@ -133,4 +135,43 @@ func (p *PebbleStateBackend) Close() error {
         return p.db.Close()
 }
 
+// Snapshot atomic
+func (p *PebbleStateBackend) Snapshot(checkpointID uint64, targetDir string) error {
+        // get parent dir
+        parentDir := filepath.Dir(targetDir)
 
+        if err := os.MkdirAll(parentDir, 0o755); err != nil {
+                return err
+        }
+
+        // create temp dir
+        tmpDir := targetDir + ".tmp"
+        _ = os.RemoveAll(tmpDir)
+
+        // rollback
+        success := false
+        defer func() {
+                if !success {
+                        _ = os.RemoveAll(tmpDir)
+                }
+        }()
+
+        if err := p.db.Checkpoint(tmpDir); err != nil {
+                return fmt.Errorf("pebble checkpoint failed for ID %d: %w", checkpointID, err)
+        }
+
+        _ = os.RemoveAll(targetDir)
+
+        if err := os.Rename(tmpDir, targetDir); err != nil {
+                return fmt.Errorf("failed to commit checkpoint atomically from %s to %s: %w", tmpDir, targetDir, err)
+        }
+
+        // fsync the parent dir
+        if parentFile, err := os.Open(parentDir); err == nil {
+                _ = parentFile.Sync()
+                _ = parentFile.Close()
+        }
+
+        success = true 
+        return nil
+}