sstables: add method to grab filter size

This is one of the statistics we need to export

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>

sstables/filter.cc

@@ -32,7 +32,11 @@ future<> sstable::read_filter() {
                 }
             }
             _filter = utils::filter::create_filter(filter.hashes, std::move(bs));
+        }).then([this] {
+            return engine().file_size(this->filename(sstable::component_type::Filter));
         });
+    }).then([this] (auto size) {
+        _filter_file_size = size;
     });
 }
 

sstables/sstables.hh

@@ -233,6 +233,9 @@ public:
     uint64_t index_size() {
         return _index_file_size;
     }
+    uint64_t filter_size() {
+        return _filter_file_size;
+    }
 
     // Returns the total bytes of all components.
     future<uint64_t> bytes_on_disk();
@@ -266,6 +269,7 @@ private:
     file _data_file;
     uint64_t _data_file_size;
     uint64_t _index_file_size;
+    uint64_t _filter_file_size = 0;
     uint64_t _bytes_on_disk = 0;
 
     sstring _ks;