Introduction To Sybase, Part 3

Writing a Sybase web application.
Backups

Just as any other part of a computer system, databases need to be backed up. One approach would be to shut down the database server, then back up the database device files. This could work, but Sybase says a back up made this way is not guaranteed to restore properly. Each database has to keep track of its logs and the sequence of transactions. If any of these are out of sync with the others, Sybase cannot use the database. Fortunately, Sybase has created a backup server to help you back up your databases. It will even let you run your backups while the database is still up. Your bookstore can stay up 24 hours a day, 7 days a week.

You can back up your databases and logs to either disk or tape using the Sybase backup server. To back up to tape, you'll need to configure your tape device. Read Chapter 18 of the System Administration Guide to learn how to configure your tape drive.

Depending on the size of your databases, I would recommend backing up the logs at least once during the day and the databases every night. If your databases are huge, you might not be able to do this. Back up the logs as often as you can, but think of log backups as changes made to the database. If the database gets corrupted, you'll need to restore the database, then all the logs you backed up since the database backup was made.

If you choose to save logs to a disk drive, I would highly recommend they be saved on a separate disk from the one holding your database. On one of our production database servers, we back up the logs to disk at noon each day, then FTP them to another system. This system has 20 1GB drives on it, so databases and logs are located on different drives, and the log backups are on yet another disk. For best performance, it would be best to keep everything on separate small drives. The system can read and write to multiple drives faster than to a large single drive.

Database Consistency

Each time you boot your Linux system, the fsck program is run against all your file systems. The fsck program makes sure all the directories and data are consistent. It is possible for a file system to become out of sync, causing a loss of data.

The Sybase database server has a similar command. It is called dbcc (database consistency check). This command makes sure all data allocations are proper and accounted for. These checks should be run regularly on your databases. They can be scheduled just as you schedule your backups.

The Bookstore Application

You can download the entire application from the Linux Journal FTP server at ftp://ftp.linuxjournal.com/pub/lj/listings/issue64/. To save space, the entire application isn't presented here. There are two tar files: 3250src.tgz and 3250cgi.tgz. The first one has the source code for all database objects. Log in as the sybase user and unpack the tar files. Read the README file before installing. You'll need to install the pubs2 example database shipped with the server. The second tar file has all CGI scripts and other files needed for the application. These files should be placed in the /cgi-bin directory of your web server. Again, read the README file before installing. Sybase and Sybperl must be installed to use this application. Information on this installation is in the first two parts of this article.

This isn't an article about web development, so I won't go into great detail about the web aspects of the application. It also isn't a web application beauty contest. You will see I didn't spend much time making it look nice. I'm sure you can find the time to make the application look the way you like it.

If you installed the application in the default location, you can start a web browser on your system and go to http://localhost/cgi-bin/store/store/ to run the application. If you receive a “File Not Found” error message, your CGI application cannot be found. On a default Red Hat 5.x system, the CGI perl script should be located at /home/httpd/cgi-bin/store/store.

If you received an Internal Server Error message, your Perl program probably isn't located at /usr/bin/perl. Edit the file /home/httpd/cgi-bin/store/store/ and modify the path for Perl to point to your Perl executable. One way to figure out the problem is to run the Perl script at the command line. You should receive HTML. If you receive an error message, you'll need to resolve this problem.

If you receive the store menu, click on Search for Books. If you receive an error message, your client cannot connect to the database. Look at the file /home/httpd/cgi-bin/store/store.inc/. You may need to change the name of the database server. Make sure your database server is up and running. You should be able to connect to it using the user name and password in the store.inc file. Use the isql program at the command line to test this.

Each screen of the application has a subroutine written in Perl. The subroutine is named after the last part of the URL. To search for books, the URL would be http://localhost/cgi-bin/store/store/search/. The subroutine responsible for this is called search.

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