vcg19.htm

Visual C++与数据库的连接经典实例

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<NOTE><B>NOTE</B>

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<BR>At the time this book was written, there were indications that Windows NT was becoming more popular in the business environment. When Microsoft introduces a version of Windows NT with the Windows 95 user interface, Windows NT might become a serious contender for the majority of the business (but not home) users of PCs.</NOTE>

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<P>Windows NT Workstation is bound to become more popular; however, it will have difficulty competing with Windows 95. Windows NT Workstation will probably be desirable only in instances in which Windows NT's enhanced robustness and security are essential.

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<P>Independent software vendors appear more optimistic than Microsoft about the future of Windows NT as a client OS. Performance of compilers and complex mega-apps can benefit greatly from 32-bit multithreaded operation. Frame Technology has announced that its FrameMaker 3.0 publishing application will be available for Windows NT. Micro Focus has introduced a COBOL compiler for Windows NT. AGE Logic supplies XoftWave/32 for Windows NT so that you can run UNIX applications in an X server environment on your PC. Welcom Software Technologies' Texim Project is a high-end project management application for Windows NT. AutoDesk, Inc., has released a version of AutoCAD for Windows NT.

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<P>The performance improvement of these types of products under Windows NT is likely to induce power users to install dual-boot Windows NT on their Windows 3.1+ workstations. Of course, the release of Windows 95 will help bring new 32-bit applications to Windows NT Workstation, because Microsoft has stated that it wants all Windows 95 applications to also run under Windows NT.

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<P>At the time this book was written, the combination of Windows NT Server 3.51 and NTSQLS had the lowest entry cost of any product combination that implements a full-featured, networked client-server computing environment. (Depending on the number of users, the cost of a Windows NT Server/NTSQLS installation is likely to be less than 25 percent of the cost of a comparable UNIX-based client-server database system.) Windows NT Server is much easier to install, administer, and maintain than any other currently available client-server NOS for enterprise-wide networks, such as Novell NetWare 4.x and Banyan VINES. NTSQLS is equally easy to install and includes server administrative tools and utilities that run under Windows on Windows NT, Windows 95, and WfWg (Windows for Workgroups) workstations. The capability to run Windows NT Server and NTSQLS on RISC-based computers using either the MIPS 4000/4400 or the Digital Alpha chipsets provides an alternative to using PCs based on Intel 80x86 MPUs (multiprocessor units). Substantial improvements in price-performance ratings of both Windows NT Server and NTSQLS are in store when the production volume of RISC-based computers speeds up in 1996 and beyond.

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<NOTE><B>NOTE</B>

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<BR>Windows NT Workstation 3.51 and Windows NT Server 3.51 also offer scalability. <I>Scalability</I> means that you can add more microprocessor (MPU) chips to a Windows NT Server (or workstation) to achieve improved performance. Windows NT Workstation and Windows NT Server can divide processing chores between up to four 80x86 MPUs. However, increasing the number of MPUs doesn't always lead to improved server performance. Many server operations, such as file replication, import, and export, are I/O bound. Adding more memory (beyond 32M) to increase the size of the disk cache often is more effective in increasing server throughput than adding more MPU chips. Other options for improving I/O include dedicated caching HD controllers and high-speed fast-wide SCSI controllers and drives. You should also consider using mirroring and/or duplexing.

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<BR>Workstations that run high-performance graphics packages (such as photo editing) also show a considerable performance improvement when the standard video card is replaced with a high-performance 32- or 64-bit video card.</NOTE>

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<FONT SIZE=4 COLOR="#FF0000"><B>Logging on to Servers and Joining Workgroups</B></FONT></CENTER></H4>

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<P>When you log on to a Windows NT Server network from a Windows NT workstation, you specify the domain you want to join in the From combo box of the Logon to Windows NT dialog box. If you're using a Windows for Workgroups 3.11 workstation or a Windows 95 workstation, you can join a workgroup and simultaneously log on to Windows NT Server when you run Windows for Workgroups by following these steps (for WfWg 3.11):

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<LI>Create an account for yourself in your Windows NT Server domain. You need to have an account with the same name and password in the Windows NT Server domain and the workgroup in order for simultaneous logon to work.

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<LI>Open the Microsoft Windows Network dialog box by double-clicking the Network icon in Control Panel's application group window.

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<LI>In the Workgroup text box, type the name of the workgroup you want to join, as shown in Figure 19.5.

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<BR><B><A HREF="19vcg05.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg05.gif">Figure 19.5. Entries in WfWg 3.11's Control Panel Network dialog box to log on to the Darkstar domain.</A></B>

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<LI>Click the Startup button to display the Startup Settings dialog box, shown in Figure 19.6. Check the Log On at Startup and Log On to Windows NT or LAN Manager Domain check boxes.

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<BR><B><A HREF="19vcg06.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg06.gif">Figure 19.6. The Startup Settings dialog box for automatic logon to a Windows NT Server domain.</A></B>

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<LI>Type your domain name in the Domain Name text box.

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<LI>If you need to change your password so that the password used by WfWg is the same as that for your Windows NT Server account, click the Set Password button and change your password.

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<LI>Click the OK button to close the Startup Settings dialog box, click the OK button in the Microsoft Windows Network dialog box to close it, and then close Control Panel. If you changed the workgroup name, the Network dialog box advises you that you need to reboot your computer in order for the change to become effective. (You don't need to reboot if you changed only the Domain Name entry in the Startup Settings dialog box.)

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<P>For Windows 95, you should follow these steps:

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<LI>Create an account for yourself in your Windows NT Server domain. You need to have an account with the same name and password in the Windows NT Server domain and the workgroup in order for simultaneous logon to work.

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<LI>Open the Microsoft Windows network dialog box by double-clicking the Network icon in Control Panel's application group window.

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<LI>Click the Identification tab in the Network dialog box, shown in Figure 19.7. Type the name of the workgroup you want to join in the Workgroup edit box.

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<BR><B><A HREF="19vcg07.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg07.gif">Figure 19.7. Entries in Windows 95's Control Panel Network dialog box to log on to the Darkstar domain.</A></B>

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<LI>Click the Access Control tab in the Network dialog box to display the Access Control settings dialog box. Choose the option you want to use.

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<LI>If you need to change your password so that the password used by Windows 95 is the same as that for your Windows NT Server account, open the Passwords dialog box from Control Panel and change your password, as shown in Figure 19.8. The Passwords dialog box lets you activate remote administration and support for user profiles.

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<BR><B><A HREF="19vcg08.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg08.gif">Figure 19.8. The Properties for Passwords dialog box in Windows 95.</A></B>

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<LI>Click the OK button to close the Network dialog box, and then close Control Panel. If you changed the workgroup name, the Network dialog box advises you that you need to reboot your computer in order for the change to become effective.

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<P>The next time you run Windows 95, the Welcome to Windows for Workgroups dialog box appears, as shown in Figure 19.9. When you enter your password and click the OK button, the Windows for Workgroup message box shown in Figure 19.10 indicates that you were successfully logged on to the domain name you chose. (\\DORA is the unified naming convention (UNC) name of the server that acts as the domain controller for the Darkstar domain.) You can skip the logon confirmation by clicking the Don't Display Message on Successful Logon check box in the Startup Settings dialog box.

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<P><B><A HREF="19vcg09.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg09.gif">Figure 19.9. The initial logon dialog box that appears when you start Windows for Workgroups 3.11 as a Windows NT Server client.</A></B>

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<P><B><A HREF="19vcg10.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg10.gif">Figure 19.10. The message box that confirms successful logon to the domain.</A></B>

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<P>If the domain controller is down or you have a network connection problem, a message box such as that shown in Figure 19.11 appears to inform you that the Windows NT Server shares you specified in File Manager to reconnect at logon weren't reconnected. Using File Manager to connect to shared files and directories is discussed later in this chapter. (Click the Yes button to preserve the reconnect at logon status of shares.) After any other failure-to-connect messages, the message box shown in Figure 19.12 appears. When you click the OK button, you are logged on to the workgroup. Any workgroup shares you specified to reconnect at startup are available to your computer, but you can't access shares on Windows NT Server(s).

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<P><B><A HREF="19vcg11.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg11.gif">Figure 19.11. The message box that indicates that a server share connection failed.</A></B>

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<P><B><A HREF="19vcg12.gif" tppabs="http://202.113.16.101/%7eeb%7e/Database%20Developer's%20Guide%20with%20Visual%20C++%204,%20Second%20Edition/19vcg12.gif">Figure 19.12. The message box that indicates a failure of the domain controller or your network connection.</A></B>

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<FONT SIZE=4 COLOR="#FF0000"><B>Server Redundancy and Backup Systems</B></FONT></CENTER></H4>

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<P>Windows NT Server provides fault tolerance for the fixed disks of network servers by employing Redundant Array of Inexpensive Disks (RAID) methodology. The following five levels (strategies) for providing fault tolerance with RAID hardware are available:

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<LI>RAID level 1, disk mirroring, uses a disk mirror set to provide an exact duplicate of data on two fixed disk drives. Disk writes to one member of the mirror set are duplicated on the other member. If one disk of the mirror set fails, Windows NT Server automatically transfers disk operations to the remaining operable disk. The advantage of disk mirroring is that only two disk drives are required; other methods of providing fault tolerance require three or more disks. Only one mirror set disk drive can have a boot sector, so you need to boot from the Windows NT recovery disk that you created when you installed Windows NT Server if the disk with the boot sector fails.

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<LI>RAID level 2 writes blocks of data across multiple disks (a process called <I>disk striping</I>) and uses an error-correcting code to regenerate good data from the data blocks on a failed drive. RAID level 2 requires at least two data disks and usually more than one disk to store the error-correction data. RAID level 2 provides a faster read data rate than level 1, but it's no longer in common use because of its inefficient method of storing data.

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<LI>RAID level 3 is a disk-striping method similar to RAID level 2, but it offers better price-performance ratings because the size of the error-correcting code is smaller. (Only one disk drive is required to store the parity information for data on the other disk drives.) RAID level 3 often is used for applications such as client-server RDBMSs that use relatively few large files.

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<LI>RAID level 4 is the same as RAID level 3, except that the blocks of striped data are larger.

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<LI>RAID level 5 uses a technique called <I>striping with parity</I>. RAID level 5 uses the large-block striping method of RAID level 4 but also stripes the parity data across all disks. Logic in the software and RAID disk controller assures that the parity information for a data block and the data block itself never reside on the same disk drive. Read performance is better than with RAID level 1, but write performance is slower because of the time required to calculate and write the parity values.