compaction: set_skip_when_empty() for validation_errors metric

Add .set_skip_when_empty() to compaction_manager::validation_errors.
This metric only increments when scrubbing encounters out-of-order or
invalid mutation fragments in SSTables, indicating data corruption.
It is almost always zero and creates unnecessary reporting overhead.

AI-Assisted: yes
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>

compaction/compaction_manager.cc

@@ -1110,7 +1110,7 @@ void compaction_manager::register_metrics() {
         sm::make_gauge("normalized_backlog", [this] { return _last_backlog / available_memory(); },
                        sm::description("Holds the sum of normalized compaction backlog for all tables in the system. Backlog is normalized by dividing backlog by shard's available memory.")),
         sm::make_counter("validation_errors", [this] { return _validation_errors; },
-                       sm::description("Holds the number of encountered validation errors.")),
+                       sm::description("Holds the number of encountered validation errors.")).set_skip_when_empty(),
     });
 }
 

db/corrupt_data_handler.cc

@@ -22,7 +22,7 @@ corrupt_data_handler::corrupt_data_handler(register_metrics rm) {
         _metrics.add_group("corrupt_data", {
                 sm::make_counter("entries_reported", _stats.corrupt_data_reported,
                                sm::description("Counts the number of corrupt data instances reported to the corrupt data handler. "
-                                                "A non-zero value indicates that the database suffered data corruption.")).set_skip_when_empty()
+                                               "A non-zero value indicates that the database suffered data corruption."))
                 });
     }
 }

db/hints/manager.cc

@@ -186,7 +186,7 @@ void manager::register_metrics(const sstring& group_name) {
             sm::description("Number of unexpected errors during sending, sending will be retried later")),
 
         sm::make_counter("corrupted_files", _stats.corrupted_files,
-                        sm::description("Number of hints files that were discarded during sending because the file was corrupted.")).set_skip_when_empty(),
+                        sm::description("Number of hints files that were discarded during sending because the file was corrupted.")),
 
         sm::make_gauge("pending_drains",
                         sm::description("Number of tasks waiting in the queue for draining hints"),

db/rate_limiter.cc

@@ -206,7 +206,7 @@ void rate_limiter_base::register_metrics() {
                 sm::description("Number of times a lookup returned an already allocated entry.")),
 
         sm::make_counter("failed_allocations", _metrics.failed_allocations,
-                sm::description("Number of times the rate limiter gave up trying to allocate.")).set_skip_when_empty(),
+                sm::description("Number of times the rate limiter gave up trying to allocate.")),
 
         sm::make_counter("probe_count", _metrics.probe_count,
                 sm::description("Number of probes made during lookups.")),

db/row_cache.cc

@@ -174,7 +174,7 @@ cache_tracker::setup_metrics() {
         sm::make_counter("sstable_reader_recreations", sm::description("number of times sstable reader was recreated due to memtable flush"), _stats.underlying_recreations),
         sm::make_counter("sstable_partition_skips", sm::description("number of times sstable reader was fast forwarded across partitions"), _stats.underlying_partition_skips),
         sm::make_counter("sstable_row_skips", sm::description("number of times sstable reader was fast forwarded within a partition"), _stats.underlying_row_skips),
-        sm::make_counter("pinned_dirty_memory_overload", sm::description("amount of pinned bytes that we tried to unpin over the limit. This should sit constantly at 0, and any number different than 0 is indicative of a bug"), _stats.pinned_dirty_memory_overload).set_skip_when_empty(),
+        sm::make_counter("pinned_dirty_memory_overload", sm::description("amount of pinned bytes that we tried to unpin over the limit. This should sit constantly at 0, and any number different than 0 is indicative of a bug"), _stats.pinned_dirty_memory_overload),
         sm::make_counter("rows_processed_from_memtable", _stats.rows_processed_from_memtable,
             sm::description("total number of rows in memtables which were processed during cache update on memtable flush")),
         sm::make_counter("rows_dropped_from_memtable", _stats.rows_dropped_from_memtable,