Oracle Database 11 g - Online Public Access Catalog

60 CHAPTER 2 ■ DATABASE DIAGNOSABILITY AND FAILURE REPAIRProblems and IncidentsThere are two new diagnostic-related concepts in Oracle Database 11g around which the entirefault diagnosability infrastructure revolves: problems and incidents. We’ll take a minute to definethese critical terms before we wade into the details of the fault diagnosability infrastructure:• Any critical error in the database is defined as a problem. Typically these include familiarOracle database errors denoted as ORA-600 errors and errors such as ORA-04031 (out ofshared pool memory). All metadata concerning a database problem is stored in the ADR.Each problem is assigned a problem key, which helps identify and describe that problem.The problem key contains the Oracle error number and error argument values. Here’san example (part of the output from a show incident command in the adrci tool, whichwe explain later in this chapter):INCIDENT_ID PROBLEM_KEY CREATE_TIME------------ ------------------ ---------------------------8801 ORA 600 [4899] 27-MAR-07 06.14.41.04-05:00• An incident is a one-time occurrence of a particular problem. Thus, if the same problemoccurs multiple times, you’ll have one problem and many incidents to denote the multipleoccurrence of that problem. A frequently occurring problem is denoted by a large numberof incidents. Each incident has its own incident ID, as shown in the previous example.The database does three things when a particular incident occurs:• It creates an alert for that incident and assigns the appropriate level of severity for thatalert.• It makes an entry regarding the incident in the alert log.• It gathers and stores the relevant diagnostic data for that incident in the appropriatesubdirectory in the ADR.You can’t disable the automatic incident creation for critical errors. A problem is createdautomatically when the first incident occurs. Once the last incident is removed from the ADR,the problem metadata is deleted as well.The ADR limits the dumping of diagnostic data to a certain number of incidents under anyone problem. Two retention policies dictate how long the ADR retains the diagnostic data itaccumulates for various incidents:• The “incident metadata retention policy” determines how long the ADR retains metadata.The default retention period is for one year.• The “incident files and dumps retention policy” determines how long the ADR retainsdump files for the incidents. The default retention period is one month.You can change either or both the retention polices using the Incident Package Configurationlink on the Support Workbench page in Database Control. The background process MMONautomatically purges expired ADR data.