Oracle Database 11 g - Online Public Access Catalog

214 CHAPTER 4 ■ PERFORMANCE MANAGEMENTThe query shows whether the plan was captured automatically or manually, as well aswhether it is accepted and enabled.You can alter any of the attributes of a SQL plan baseline by using the DBMS_SPM.ALTER_SQL_PLAN_BASELINE function. You can also import and export SQL plan baselines using Oracle DataPump and procedures from the DBMS_SPM package.ADDM EnhancementsIn Oracle Database 10g, Oracle introduced the Automatic Database Diagnostic Monitor, whichuses the automatic workload repository snapshots to provide diagnosis regarding SQL statements,IO, and CPU usage in the database. The ADDM is based on the single-minded goal toreduce “DB time.” ADDM provides you with quick results that help pinpoint the root cause ofa performance problem, besides telling you what the nonproblem areas are, so you don’t wasteyour time chasing down unproductive avenues.Instance ADDM and Database ADDMYou can run the ADDM in two distinct modes in Oracle Database 11g. In the first mode, calledthe instance ADDM, the monitor provides traditional instance-level performance evaluation.The instance ADDM is what you have in Oracle Database 10g. Oracle calls the new ADDMmode introduced in the new release database ADDM, and its goal is to analyze and report onOracle RAC installations. In this mode, the ADDM report will contain an analysis of the clusteras a unit besides an analysis of each of the instances that are part of the the cluster. Oracle’starget for the database ADDM is database administrators rather than application developers,for whom the instance ADDM is more relevant.The instance ADDM runs automatically after the database takes each AWR snapshot, andit produces the same reports that it did in the Oracle Database 10g database. Depending onwhether you run the ADDM in global or instance mode, you’ll have global findings or localfindings.The global ADDM is appropriate only for an ORAC setup, where the tool can analyze theperformance of the entire cluster together as one unit. For example, the DB time is computedas the sum of the database times for all instances in the ORAC cluster. Global ADDM also reportsfacts such as CPU consumption and server performance at the aggregate cluster level, thusgiving you an overall view of how the ORAC installation is performing. You can also perform apartial analysis of just a subset of the instances in a cluster. This is known as the partial analysisADDM. If you are concerned about the performance of only some but not all instances in acluster, partial analysis ADDM will provide results faster than an exhaustive database ADDManalysis.Running ADDM Over a Specific Time PeriodYou can now run an ADDM task for any specific range of time you want, instead of being ableto run it only over a pair of snapshots. This is a great help, especially when there is a hung databaseor a sharp spike in activity in the database that hasn’t been captured yet by an AWR snapshot.