chore(pageserver): concise error message for layer traversal (#7565)

Instead of showing the full path of layer traversal, we now only show
tenant (in tracing context)+timeline+filename.

---------

Signed-off-by: Alex Chi Z <chi@neon.tech>

pageserver/src/tenant/storage_layer/layer.rs

@@ -401,8 +401,8 @@ impl Layer {
         &self.0.path
     }
 
-    pub(crate) fn local_path_str(&self) -> &Arc<str> {
-        &self.0.path_str
+    pub(crate) fn debug_str(&self) -> &Arc<str> {
+        &self.0.debug_str
     }
 
     pub(crate) fn metadata(&self) -> LayerFileMetadata {
@@ -527,8 +527,8 @@ struct LayerInner {
     /// Full path to the file; unclear if this should exist anymore.
     path: Utf8PathBuf,
 
-    /// String representation of the full path, used for traversal id.
-    path_str: Arc<str>,
+    /// String representation of the layer, used for traversal id.
+    debug_str: Arc<str>,
 
     desc: PersistentLayerDesc,
 
@@ -735,7 +735,7 @@ impl LayerInner {
 
         LayerInner {
             conf,
-            path_str: path.to_string().into(),
+            debug_str: { format!("timelines/{}/{}", timeline.timeline_id, desc.filename()).into() },
             path,
             desc,
             timeline: Arc::downgrade(timeline),

pageserver/src/tenant/timeline.rs

@@ -2948,7 +2948,7 @@ trait TraversalLayerExt {
 
 impl TraversalLayerExt for Layer {
     fn traversal_id(&self) -> TraversalId {
-        Arc::clone(self.local_path_str())
+        Arc::clone(self.debug_str())
     }
 }