row_cache: count read row tombstones

Refs #7749.

Signed-off-by: Michael Livshin <michael.livshin@scylladb.com>

cache_flat_mutation_reader.hh

@@ -701,6 +701,9 @@ void cache_flat_mutation_reader::add_clustering_row_to_buffer(mutation_fragment&
     push_mutation_fragment(std::move(mf));
     _lower_bound = std::move(new_lower_bound);
     _lower_bound_changed = true;
+    if (row.tomb()) {
+        _read_context.cache()._tracker.on_row_tombstone_read();
+    }
 }
 
 inline

db/cache_tracker.hh

@@ -78,6 +78,7 @@ public:
         uint64_t reads_done;
         uint64_t pinned_dirty_memory_overload;
         uint64_t range_tombstone_reads;
+        uint64_t row_tombstone_reads;
 
         uint64_t active_reads() const {
             return reads - reads_done;
@@ -120,6 +121,7 @@ public:
     void on_row_dropped_from_memtable() noexcept { ++_stats.rows_dropped_from_memtable; }
     void on_row_merged_from_memtable() noexcept { ++_stats.rows_merged_from_memtable; }
     void on_range_tombstone_read() noexcept { ++_stats.range_tombstone_reads; }
+    void on_row_tombstone_read() noexcept { ++_stats.row_tombstone_reads; }
     void pinned_dirty_memory_overload(uint64_t bytes) noexcept;
     allocation_strategy& allocator() noexcept;
     logalloc::region& region() noexcept;

row_cache.cc

@@ -138,6 +138,8 @@ cache_tracker::setup_metrics() {
             sm::description("total number of rows in memtables which were merged with existing rows during cache update on memtable flush")),
         sm::make_derive("range_tombstone_reads", _stats.range_tombstone_reads,
             sm::description("total amount of range tombstones processed during read")),
+        sm::make_derive("row_tombstone_reads", _stats.row_tombstone_reads,
+            sm::description("total amount of row tombstones processed during read")),
     });
 }