Implement connection caching and checking (requires ODBCv3 driver)

Implement preferLocal DB access

2 files changed, 82 insertions, 15 deletions

diff --git a/project2/rdbmsDataSource.cpp b/project2/rdbmsDataSource.cpp
index 1a55fb8..ab515a1 100644
--- a/project2/rdbmsDataSource.cpp
+++ b/project2/rdbmsDataSource.cpp
@@ -1,48 +1,105 @@
 #include "rdbmsDataSource.h"
 #include "xmlObjectLoader.h"
 #include <libxml++/nodes/textnode.h>
+#include <sys/utsname.h>
+#include <syslog.h>
+#include <errno.h>
+#include <sqlext.h>
+
+_RdbmsDataSource::DBHosts _RdbmsDataSource::dbhosts;
 
 _RdbmsDataSource::_RdbmsDataSource(const xmlpp::Element * p) :
 	_SourceObject(p),
 	_DataSource(p),
-	masterDsn(xmlChildText(p, "masterdsn"))
+	masterDsn(xmlChildText(p, "masterdsn")),
+	preferLocal(p->get_attribute_value("preferlocal") != "false")
 {
+	BOOST_FOREACH(const xmlpp::Node * node, p->find("readonly/dsn")) {
+		const xmlpp::Element * elem = dynamic_cast<const xmlpp::Element *>(node);
+		if (elem) {
+			roDSNs[elem->get_attribute_value("host")] = elem->get_child_text()->get_content();
+		}
+	}
 }
 
 ODBC::Connection &
 _RdbmsDataSource::getWritable() const
 {
-	if (!database) {
-		database = boost::shared_ptr<ODBC::Connection>(new ODBC::Connection(masterDsn));
+	ConnectionPtr master = connectTo(masterDsn);
+	if (!master->inTx()) {
+		master->beginTx();
 	}
-	if (!database->inTx()) {
-		database->beginTx();
-	}
-	return *database;
+	return *master;
 }
 
 ODBC::Connection &
 _RdbmsDataSource::getReadonly() const
 {
-	if (!database) {
-		database = boost::shared_ptr<ODBC::Connection>(new ODBC::Connection(masterDsn));
+	if (localhost.length() == 0 && preferLocal) {
+		struct utsname name;
+		if (uname(&name)) {
+			syslog(LOG_WARNING, "%s: Unable to determine local host name (%d:%s)", __FUNCTION__, errno, strerror(errno));
+			localhost = "unknown";
+		}
+		else {
+			localhost = name.nodename;
+		}
+	}
+	if (preferLocal) {
+		ReadonlyDSNs::const_iterator ro = roDSNs.find(localhost);
+		if (ro == roDSNs.end()) {
+			syslog(LOG_WARNING, "%s: No database host makes local host name (%s) Will use master DSN", __FUNCTION__, localhost.c_str());
+			return *connectTo(masterDsn);
+		}
+		return *connectTo(ro->second);
+	}
+	else {
+		BOOST_FOREACH(ReadonlyDSNs::value_type db, roDSNs) {
+			try {
+				return *connectTo(db.second);
+			}
+			catch (...) {
+			}
+		}
+		return *connectTo(masterDsn);
 	}
-	return *database;
 }
 
 void
 _RdbmsDataSource::commit()
 {
-	if (database && database->inTx()) {
-		database->commitTx();
+	DBHosts::const_iterator m = dbhosts.find(masterDsn);
+	if (m != dbhosts.end() && m->second->inTx()) {
+		m->second->commitTx();
 	}
 }
 
 void
 _RdbmsDataSource::rollback()
 {
-	if (database && database->inTx()) {
-		database->rollbackTx();
+	DBHosts::const_iterator m = dbhosts.find(masterDsn);
+	if (m != dbhosts.end() && m->second->inTx()) {
+		m->second->rollbackTx();
+	}
+}
+_RdbmsDataSource::ConnectionPtr
+_RdbmsDataSource::connectTo(const std::string & dsn)
+{
+	DBHosts::const_iterator dbi = dbhosts.find(dsn);
+	if (dbi != dbhosts.end()) {
+		try {
+			SQLINTEGER dead = dbi->second->getAttrInt(SQL_ATTR_CONNECTION_DEAD);
+			if (dead == SQL_CD_FALSE) {
+				return dbi->second;
+			}
+		}
+		catch (...) {
+			// Connection in failed state
+			syslog(LOG_WARNING, "%s: Cached connection failed", __FUNCTION__);
+		}
 	}
+	ConnectionPtr db = ConnectionPtr(new ODBC::Connection(dsn));
+	dbhosts[dsn] = db;
+	return db;
 }
 
diff --git a/project2/rdbmsDataSource.h b/project2/rdbmsDataSource.h
index ee75550..e5709b7 100644
--- a/project2/rdbmsDataSource.h
+++ b/project2/rdbmsDataSource.h
@@ -9,14 +9,24 @@
 
 class _RdbmsDataSource : public _DataSource {
 	public:
+		typedef boost::shared_ptr<ODBC::Connection> ConnectionPtr;
+		typedef std::map<std::string, std::string> ReadonlyDSNs; // Map hostname to DSN string
+		typedef std::map<std::string, ConnectionPtr> DBHosts; // Map DSN strings to connections
 		_RdbmsDataSource(const xmlpp::Element * p);
 		ODBC::Connection & getReadonly() const;
 		ODBC::Connection & getWritable() const;
 		virtual void commit();
 		virtual void rollback();
 		const std::string masterDsn;
+		const bool preferLocal;
+
+	protected:
+		static ConnectionPtr connectTo(const std::string & dsn);
+		ReadonlyDSNs roDSNs;
+
 	private:
-		mutable boost::shared_ptr<ODBC::Connection> database;
+		mutable std::string localhost;
+		static DBHosts dbhosts;
 };
 typedef boost::shared_ptr<_RdbmsDataSource> RdbmsDataSource;
 typedef std::map<std::string, RdbmsDataSource> RdbmsDataSources;