eG Monitoring
 

Measures reported by OraExePlnStTest

The EXPLAIN PLAN statement displays execution plans chosen by the Oracle optimizer for SELECT, UPDATE, INSERT, and DELETE statements. A statement's execution plan is the sequence of operations Oracle performs to run the statement.

The Oracle optimizer plays a key role in query processing and decides the most optimal explain plan for the queries that wanted to execute. The optimizer estimates the resource consumption cost of the explain plan candidates and chooses the effective and cheap plan in terms of I/O, memory, CPU, and time. In the process, the Oracle optimizer also changes the plans during query processing when any of the following things happen on a running instance:

  • Re-run of dbms_stats for CBO statistics,

  • Alter table commands

  • Adding/dropping an index

  • Using dynamic sampling

  • Parallelism is enabled

Sometimes, query processing may be delayed when the explain plan decided by the Oracle Optimizer is used for execution. This may lead to query processing bottlenecks. To avoid such bottlenecks, it is necessary for the administrators to keep track on the explain plans that were changed during query execution. The OraExePlnStTest helps administrators in this regard!

This test periodically monitors the target Oracle database server and reports the number of times that the explain plans were changed during query execution. The detailed diagnosis reported by this test reveals the details on plan changes for each query, name of all the plans used for each query, etc.

Outputs of the test : One set of results for the Oracle server that is being monitored

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
ExplainPlanChangeCount Indicates the number of times the explain plans were changed during the last measurement period. Number The detailed diagnosis of this measure reveals the session ID, user name, database name, host name, count of unique plans, name of old and new explain plans and brief description about the query.
RateofExePlanChange Indicates the rate at which explain plans were changed during the last measurement period. Plans/second