ircd::db: Add cache clear interface w/ console cmd.

include/ircd/db/cache.h

@@ -41,6 +41,10 @@ namespace ircd::db
 	void remove(rocksdb::Cache &, const string_view &key);
 	void remove(rocksdb::Cache *const &, const string_view &key);
 
+	// Clear the cache (won't clear entries which are actively referenced)
+	void clear(rocksdb::Cache &);
+	void clear(rocksdb::Cache *const &);
+
 	// Iterate the cache entries.
 	using cache_closure = std::function<void (const string_view &, const size_t &)>;
 	void for_each(rocksdb::Cache &, const cache_closure &);

ircd/db.cc

@@ -5178,6 +5178,19 @@ ircd::db::for_each(rocksdb::Cache &cache,
 	false);
 }
 
+void
+ircd::db::clear(rocksdb::Cache *const &cache)
+{
+	if(cache)
+		clear(*cache);
+}
+
+void
+ircd::db::clear(rocksdb::Cache &cache)
+{
+	cache.EraseUnRefEntries();
+}
+
 void
 ircd::db::remove(rocksdb::Cache *const &cache,
                  const string_view &key)

modules/console.cc

@@ -1422,6 +1422,61 @@ catch(const std::out_of_range &e)
 	return true;
 }
 
+bool
+console_cmd__db__cache__clear(opt &out, const string_view &line)
+try
+{
+	const params param{line, " ",
+	{
+		"dbname", "column"
+	}};
+
+	const auto dbname
+	{
+		param.at(0)
+	};
+
+	const auto colname
+	{
+		param[1]
+	};
+
+	auto &database
+	{
+		*db::database::dbs.at(dbname)
+	};
+
+	const auto clear{[&out, &database]
+	(const string_view &colname)
+	{
+		db::column column
+		{
+			database, colname
+		};
+
+		db::clear(cache(column));
+		db::clear(cache_compressed(column));
+		out << "Cleared caches for '" << name(database) << "' '" << colname << "'"
+		    << std::endl;
+	}};
+
+	if(!colname || colname == "**")
+	{
+		for(const auto &colname : database.column_names)
+			clear(colname);
+
+		return true;
+	}
+
+	clear(colname);
+	return true;
+}
+catch(const std::out_of_range &e)
+{
+	out << "No open database by that name" << std::endl;
+	return true;
+}
+
 bool
 console_cmd__db__stats(opt &out, const string_view &line)
 {