db: handle multi-row INSERTs

Several database implementations, including, e.g., MySQL and PostgreSQL,
allow multiple rows to be INSERTed at once.  At least for MySQL this
improves INSERT speed significantly.

Change-Id: Ic223f7915053f30b0cb00c567310f3e780c9fa59

src/core/util/Database.cc

@@ -21,6 +21,14 @@ Database::Database(const std::string &username, const std::string &host, const s
 	LOG << "opened MYSQL connection" << std::endl;
 }
 
+Database::~Database()
+{
+	// flush cached INSERTs if available
+	insert_multiple();
+
+	mysql_close(handle);
+}
+
 MYSQL_RES* Database::query(char const *query, bool get_result) {
 #ifndef __puma
 	boost::lock_guard<boost::mutex> guard(m_handle_lock);
@@ -67,6 +75,43 @@ MYSQL_RES* Database::query_stream(char const *query)
 	return res;
 }
 
+bool Database::insert_multiple(char const *insertquery, char const *values)
+{
+	// different insertquery, but still cached values?
+	if (insertquery && m_insertquery != insertquery && m_insertquery_values.size() > 0) {
+		// flush cache
+		insert_multiple();
+	} else if (!insertquery && m_insertquery.size() == 0) {
+		// don't know how to INSERT, no insertquery available!
+		return false;
+	}
+
+	if (insertquery) {
+		m_insertquery = insertquery;
+	}
+
+	if (values) {
+		m_insertquery_values.push_back(values);
+	}
+
+	if ((!values && m_insertquery_values.size() > 0) || m_insertquery_values.size() >= 32) {
+		std::stringstream sql;
+		sql << m_insertquery;
+		bool first = true;
+		for (std::vector<std::string>::const_iterator it = m_insertquery_values.begin();
+		     it != m_insertquery_values.end(); ++it) {
+			if (!first) {
+				sql << ",";
+			}
+			first = false;
+			sql << *it;
+		}
+		m_insertquery_values.clear();
+		return query(sql.str().c_str());
+	}
+
+	return true;
+}
 
 my_ulonglong Database::affected_rows()
 {

src/core/util/Database.hpp

@@ -24,13 +24,15 @@ namespace fail {
 #ifndef __puma
 		boost::mutex m_handle_lock;
 #endif
+		std::string m_insertquery;
+		std::vector<std::string> m_insertquery_values;
 
 	public:
 		/**
 		 * Constructor that connects instantly to the database
 		 */
 		Database(const std::string &username, const std::string &host, const std::string &database);
-		~Database() { mysql_close(handle); }
+		~Database();
 
 		struct Variant {
 			int id;
@@ -80,6 +82,12 @@ namespace fail {
 		 */
 		MYSQL_RES *query_stream(char const *query);
 
+		/**
+		 * Caches multiple value tuples to combine into multi-value INSERTs.
+		 * Call without parameters to flush the cache.
+		 */
+		bool insert_multiple(char const *insertquery = 0, char const *values = 0);
+
 		/**
 		 * How many rows were affected by the last query
 		 */