pageserver: deletion queue nits

pageserver/src/deletion_queue/list_writer.rs

@@ -243,11 +243,7 @@ impl ListWriter {
             let file_name = dentry.file_name();
             let dentry_str = file_name.to_string_lossy();
 
-            if Some(file_name.as_os_str()) == header_path.file_name() {
-                // Don't try and parse the header's name like a list
-                continue;
-            }
-
+            // Temporary files might be left behind from `crashsafe_overwrite`
             if dentry_str.ends_with(TEMP_SUFFIX) {
                 info!("Cleaning up temporary file {dentry_str}");
                 let absolute_path = deletion_directory.join(dentry.file_name());
@@ -263,6 +259,11 @@ impl ListWriter {
                 continue;
             }
 
+            if Some(file_name.as_os_str()) == header_path.file_name() {
+                // Don't try and parse the header's name like a list
+                continue;
+            }
+
             let file_name = dentry.file_name().to_owned();
             let basename = file_name.to_string_lossy();
             let seq_part = if let Some(m) = list_name_pattern.captures(&basename) {

pageserver/src/deletion_queue/validator.rs

@@ -116,6 +116,11 @@ where
     /// Valid LSN updates propagate back to Timelines immediately, valid DeletionLists
     /// go into the queue of ready-to-execute lists.
     async fn validate(&mut self) -> Result<(), DeletionQueueError> {
+        // Figure out for each tenant which generation number to validate.
+        //
+        // It is sufficient to validate the max generation number of each tenant because only the
+        // highest generation number can possibly be valid. Hence this map will collect the
+        // highest generation pending validation for each tenant.
         let mut tenant_generations = HashMap::new();
         for list in &self.pending_lists {
             for (tenant_id, tenant_list) in &list.tenants {
@@ -246,6 +251,11 @@ where
                 }
             }
 
+            // Assert monotonicity of the list sequence numbers we are processing
+            if let Some(validated) = validated_sequence {
+                assert!(list.sequence >= validated)
+            }
+
             validated_sequence = Some(list.sequence);
         }