ircd::db: Add custom cache stats ticker.

include/ircd/db/cache.h

@@ -21,6 +21,12 @@
 
 namespace ircd::db
 {
+	struct cache_stats;
+
+	// Get our stats
+	const cache_stats &stats(const rocksdb::Cache &);
+	cache_stats stats(const rocksdb::Cache *const &);
+
 	// Get capacity
 	size_t capacity(const rocksdb::Cache &);
 	size_t capacity(const rocksdb::Cache *const &);
@@ -58,3 +64,13 @@ namespace ircd::db
 	void clear(rocksdb::Cache &);
 	void clear(rocksdb::Cache *const &);
 }
+
+/// Our custom cache statistics. Though the rocksdb::Statistics ticker could
+/// be instantiated for each cache we have our own counters, and we let the
+/// rocksdb cache impl update our database ticker instead for aggregate stats.
+struct ircd::db::cache_stats
+{
+	size_t inserts {0};
+	size_t misses {0};
+	size_t hits {0};
+};

include/ircd/db/database/cache.h

@@ -34,6 +34,7 @@ final
 	static const bool DEFAULT_STRICT;
 
 	database *d;
+	cache_stats stats;
 	std::shared_ptr<rocksdb::Cache> c;
 
 	const char *Name() const noexcept override;

ircd/db.cc

@@ -2066,7 +2066,13 @@ ircd::db::database::cache::Insert(const Slice &key,
 noexcept
 {
 	assert(bool(c));
-	return c->Insert(key, value, charge, del, handle, priority);
+	const rocksdb::Status &ret
+	{
+		c->Insert(key, value, charge, del, handle, priority)
+	};
+
+	stats.inserts += ret.ok();
+	return ret;
 }
 
 rocksdb::Cache::Handle *
@@ -2075,7 +2081,14 @@ ircd::db::database::cache::Lookup(const Slice &key,
 noexcept
 {
 	assert(bool(c));
-	return c->Lookup(key, statistics);
+	auto *const &ret
+	{
+		c->Lookup(key, statistics)
+	};
+
+	stats.hits += bool(ret);
+	stats.misses += !bool(ret);
+	return ret;
 }
 
 bool
@@ -8217,6 +8230,23 @@ ircd::db::capacity(const rocksdb::Cache &cache)
 	return cache.GetCapacity();
 }
 
+ircd::db::cache_stats
+ircd::db::stats(const rocksdb::Cache *const &cache)
+{
+	return cache? stats(*cache) : cache_stats{};
+}
+
+const ircd::db::cache_stats &
+ircd::db::stats(const rocksdb::Cache &cache)
+{
+	const auto &dc
+	{
+		dynamic_cast<const database::cache &>(cache)
+	};
+
+	return dc.stats;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // Misc