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There are several data dictionary views that provide information about database metrics and alerts. I ve already mentioned the V$SYSMETRIC, V$SERVICEMETRIC, and V$SYSMETRIC_HISTORY views earlier in this chapter. Following are some of the other key views: V$METRICNAME shows the mapping of metric names to metric IDs. V$ALERT_TYPES displays information about server alert types. DBA_HIST_SYSMETRIC_HISTORY contains snapshots of V$SYSMETRIC_HISTORY. DBA_ALERT_HISTORY provides a history of alerts that are no longer outstanding; that is, all alerts that you have already resolved. DBA_OUTSTANDING_ALERTS contains all the threshold alerts that have yet to be resolved. DBA_THRESHOLDS shows the names as well as the critical and warning values for all thresholds in the database. I ll describe a couple of the important views in more detail in the following sections.

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The V$ALERT_TYPES view provides information about all system alert types. Three columns in this view are noteworthy: STATE: Holds two possible values: stateful or stateless. Stateful alerts are those alerts that clear automatically when the alert threshold that prompted the alert is cleared. The database considers all the nonthreshold alerts as stateless alerts. A stateful alert first appears in the DBA_OUTSTANDING_ALERTS view and goes to the DBA_ALERT_HISTORY view when it is cleared. A stateless alert goes straight to DBA_ALERT_HISTORY. SCOPE: Classifies alerts into database-wide and instance-wide. The only database-level alert is the one based on the tablespace space usage metric. All the other alerts are at the instance level. GROUP_NAME: Oracle aggregates the various database alerts into some common groups: space, performance, and configuration.

Several utilities in UNIX make copies or restore files from copies. Of these, the dd command pertains mainly to the so-called raw files. Most of the time, you ll be dealing with UNIX file systems, and you ll need to be familiar with two important archiving facilities tar and cpio to perform backups and restores. Tar is an abbreviation for tape file archiver, and was originally designed to write to tapes. Cpio stands for copy input and output. Other methods such as fbackup/frecover, dump/restore, and xdump/vxrestore exist, but they are mainly of interest to UNIX administrators. You most likely will use the tar and cpio commands to perform backups. The tar command can copy and restore archives of files using a tape system or a disk drive. By default, tar output is placed on /dev/rmt/Om, which refers to a tape drive. The following tar command will copy the data01.dbf file to a tape, which is specified in the format /dev/rmt/0m. The -cvf option creates a new archive (the hyphen is optional). The c option asks tar to create a new archive file, and the v option stands for verbose, which specifies that the files be listed as they are being archived: $ tar -cvf /dev/rmt/0m /u10/oradata/data/data01.dbf

The following tar command will extract the backed-up files from the tape to the specified directory: $ tar -xvf/dev/rmt/0m /u20/oradata/data/data01.dbf

The x option asks tar to extract the contents of the specified file. The v and f options have the same meanings as in the previous example. The cpio command with the -o (copy out) option copies files to standard output, such as disk or tape. The following command will copy the contents of the entire current directory (all the files) to the /dev/rmt/0m tape: $ ls | cpio -0 > /dev/rmt/0m The cpio command with the -i (copy in) option extracts files from standard input. The following command restores all the contents of the specified tape to the current directory: $ cpio -i < /dev/rmt/0m

Next the user variable is set to the username and the corresponding home directory is found by searching the /etc/passwd file. Once again, if you are in an NIS environment, you will need to modify this command appropriately.

Most DBAs will have to schedule their shell programs and other data-loading programs for regular execution by the UNIX system. UNIX provides the cron table, or crontab, to schedule database tasks. In this section, you ll learn how to schedule jobs with this wonderful, easy-to-use utility. You can invoke the crontab by typing in crontab -l. This will give you a listing of the contents of crontab. To add programs to the schedule or change existing schedules, you need to invoke crontab in the edit mode, as shown here: $ crontab -e Each line in the crontab is an entry for a regularly scheduled job or program, and you edit the crontab the same way you edit any normal vi-based file. Each line in the /etc/crontab file represents a job that you want to execute, and it has the following format: Minute hour day month day of week command