负载均衡

// Demonstrate enabling native load connection balancing.
// Standard i/o library
#include <stdlib.h>
#include <iostream>
#include <assert.h>
// Only needed for Windows clients
// #include <windows.h>
// SQL include files that define data types and ODBC API
// functions
#include <sql.h>
#include <sqlext.h>
#include <sqltypes.h>

using namespace std;
int main()
{
    SQLRETURN ret;   // Stores return value from ODBC API calls
    SQLHENV hdlEnv;  // Handle for the SQL environment object
    // Allocate an a SQL environment object
    ret = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &hdlEnv);
    assert(SQL_SUCCEEDED(ret));

    // Set the ODBC version we are going to use to
    // 3.
    ret = SQLSetEnvAttr(hdlEnv, SQL_ATTR_ODBC_VERSION,
            (SQLPOINTER) SQL_OV_ODBC3, SQL_IS_UINTEGER);
    assert(SQL_SUCCEEDED(ret));

    // Allocate a database handle.
    SQLHDBC hdlDbc;
    ret = SQLAllocHandle(SQL_HANDLE_DBC, hdlEnv, &hdlDbc);
    assert(SQL_SUCCEEDED(ret));

    // Connect four times. If load balancing is on, client should
    // connect to different nodes.
    for (int x=1; x <= 4; x++) {

        // Connect to the database using SQLDriverConnect. Set
        // ConnectionLoadBalance to 1 (true) to enable load
        // balancing.
        cout << endl << "Connection attempt #" << x << "... ";
        const char *connStr = "DSN=VMart;ConnectionLoadBalance=1;"
            "UID=ExampleUser;PWD=password123";


        ret = SQLDriverConnect(hdlDbc, NULL, (SQLCHAR*)connStr, SQL_NTS,
               NULL, 0, NULL, SQL_DRIVER_NOPROMPT );
        if(!SQL_SUCCEEDED(ret)) {
            cout << "failed. Exiting." << endl;
            exit(EXIT_FAILURE);
        } else {
            cout << "succeeded" << endl;
        }
        // We're connected. Query the v_monitor.current_session table to
        // find the name of the node we've connected to.

        // Set up a statement handle
        SQLHSTMT hdlStmt;
        SQLAllocHandle(SQL_HANDLE_STMT, hdlDbc, &hdlStmt);
        assert(SQL_SUCCEEDED(ret));

        ret = SQLExecDirect( hdlStmt, (SQLCHAR*)"SELECT node_name FROM "
            "V_MONITOR.CURRENT_SESSION;", SQL_NTS );

        if(SQL_SUCCEEDED(ret)) {
            // Bind varible to column in result set.
            SQLTCHAR node_name[256];
            ret = SQLBindCol(hdlStmt, 1, SQL_C_TCHAR, (SQLPOINTER)node_name,
                sizeof(node_name), NULL);
            while(SQL_SUCCEEDED(ret = SQLFetchScroll(hdlStmt, SQL_FETCH_NEXT,1))) {
                // Print the bound variables, which now contain the values from the
                // fetched row.
                cout << "Connected to node " << node_name << endl;
            }
        }
        // Free statement handle
        SQLFreeHandle(SQL_HANDLE_STMT,hdlStmt);
        cout << "Disconnecting." << endl;
        ret = SQLDisconnect( hdlDbc );
        assert(SQL_SUCCEEDED(ret));
    }
    // When done, free all of the handles to close them
    // in an orderly fashion.
    cout << endl << "Freeing handles..." << endl;
    SQLFreeHandle(SQL_HANDLE_DBC, hdlDbc);
    SQLFreeHandle(SQL_HANDLE_ENV, hdlEnv);
    cout << "Done!" << endl;
    exit(EXIT_SUCCESS);
}