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Oracle Developer and User Responsibilities

Oracle Database Tips by Donald Burleson

We?ve already looked at the responsibilities of the DBA or administrative user; now we need to answer what are the normal responsibilities of the other user types? According to the Oracle8 Server Administrator's Guide, they are:

Developmental Responsibilities

1.      Design and develop database applications.

2.      Design the database structure for an application.

3.      Estimate storage requirements for an application.

4.      Specify modifications of the database structures for an application.

5.      Keep the database administrator informed of required changes.

6.      Tune the application (not the database!) during development.

7.      Establish an application's security requirements during development.

Application User's Responsibilities

1.      Enter, modify, and delete data, where permitted.

2.      Generate reports of data.

All Oracle databases have three types of users: administrative, developmental, and application. As their names imply, administrative users administer and maintain the database itself; developmental users develop applications and systems; and application users use the developed applications and systems.

These three types of users have different needs. The space and disk needs of a developer are usually greater than those of an application user. A developer system may get by with a smaller SGA because, generally speaking, developers will work with a subset of all the data expected, while a production database user will need a larger SGA because the data set is much larger. Administrative users usually have the same quotas as a developmental user, but their privileges are greater.

The number of each of these types of users will tell you about required SGA sizing, disk resource requirements, and required system memory.

What Is the Number and Placement of Control Files? 

Control files are probably the smallest and most important files in the Oracle system. They contain the following data:

* Names of the database and redo log files

* Timestamp of database creation

* Begin/end of rollback segments

* Checkpoint information

* Current redo log file sequence number

 This data is critical for database operation, and at least one control file is required for database startup. There are methods for rebuilding a control file, but it is much easier to maintain--or rather have Oracle maintain--multiple copies of the control file.

Oracle recommends two copies on separate disk resources. For OFA compliance, three are required. Obviously, if they are on the same platter or are placed in the same stripe set, the same disaster can waste all of them; therefore, they should be placed on different physical disk arrays if possible. More than three copies is a bit paranoid, but if it makes you feel safer, have as many as you wish; only one usable, current file is required for startup.

What Is the Number and Placement of Redo Logs? 

Oracle requires at least two groups of one redo log. If you are archiving, three are suggested. In a number of installations, up to six or more have been defined. If you do a lot of update activity and have numerous users, more than six may be required. When a log fills, the next one in the queue is opened, and the previously active log is marked for archive (if you have archiving enabled). The logs are archived on a first-in, first-out basis, so, depending on the speed that the log groups can be written to disk or tape, more than one log group may be waiting to be archived. One redo log group is used at a time, with multiple users writing into it at the same time. The size of the redo logs in a group depends on one critical piece of data: How much data can you afford to lose on a system crash?

You see, the smaller the log group size, the more often it is written to disk and the less data (time-wise) is lost. The larger the log group size, the less often it is written to disk and the more data (time-wise) is lost. For instance, if your log groups are filling every 10 minutes, then you may lose 10 minutes? worth of data should the disk(s) crash that holds that redo log group's files. It has been demonstrated on an active system that a 100-MB redo log group may only last a few seconds. In an inactive or read-only-type situation, a 100-MB redo log may last for hours. It is all dependent on how the database is being used and the size of the redo log group. Remember, a group of three 100-MB redo logs is actually treated as only a single 100-MB redo log (the other two files are mirrors). If you mirror redo logs by placing the group members on separate disks (not just on separate file systems; be sure it is separate physical disks), then your ability to recover from a disk array or controller crash increases manyfold.

You have to balance the needs for restoration and minimal data loss against time to recover data. Obviously, if you have archiving happening every minute and your normal workday is eight hours, you will have 480 logs written to disk daily. Over a five-day workweek, this turns into 2,400 files. If you have to restore from a crash or other disaster, you may have to apply all of these to your last backup to bring the database current to the time of the crash. In one case, a DBA had to apply 9,000-plus files to recover his system because he hadn't looked at how often his redo logs were archiving. Needless to say, he pays more attention now. The minimum size for redo log groups is 50 KB. By default the Oracle9i DBCA creates 100 megabyte redo log

In Chapter 12 on database tuning, we will discuss how to determine if you have a sufficient number of redo log groups and how to optimize your archive process.

This is an excerpt from Mike Ault, bestselling author of "Oracle 10g Grid and Real Application Clusters".



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