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Spotlight on Oracle 10.4 - Release Notes

Parallel Query Sessions Page

Parallel Query Sessions shows details of the parallel queries executed for all users connected to the Oracle RAC Cluster.

In a serial query on an Oracle database, a single process executes a SQL statement on a table in the database. Parallel query execution performs the same task by using a single master process (the parallel query server) to coordinate slave processes that execute multiple copies of a query on separate sections of that table at the same time. The master process then sends the results of the queries back to the user.

To open the Parallel Query Sessions page

  1. Select the Spotlight on Oracle RAC connection in the Spotlight Browser.

  2. Click Top Sessions | Parallel Query Sessions.

Charts on the Parallel Query Sessions page

Chart Description
Parallel Query Degree

Use the Parallel Query Degree chart to see if demand for parallel processes (the Requested degree) is higher than the actual number used (the Degree).

Tip: You can see the sessions that are running in the Parallel Query Sessions grid.

Note: The number of processes used (the Degree) may be greater than the sum of the processes on each instance because of PZnn processes that are spawned by Oracle to do queries on GV$ views.

Parallel Queue Wait Times

Note: Applies only to Oracle 11g Release 2.

  • Maximum queued time - Answers the question: of all items in the queue (for all the instances in the cluster), which has been waiting the longest?

    Note: Data on the chart is refreshed at the foreground rate - not continuous - which can lead to the effect of a spike on the chart where an item enters the queue in one refresh and leaves in the next.

  • Average queue wait - Answers the question: Since the Oracle session started, how long on average have items waited in the queue? This measures the average wait across the cluster.

Tip: You can see the sessions that are running in the Parallel Execution Queue grid.

Parallel Query Operations

Note: Applies only to Oracle 11gR1 and earlier.

When a user executes a set of parallel queries on a database, the lack of available resources may cause those queries to be downgraded or serialized.

Query Types:

  • Downgraded - When the original parallel query server initiates a number of parallel queries on a database table, the lack of resources may limit the number of queries actually executed. For example, when a server requests four parallel queries, but only two can be run, the queries have been downgraded from four to two.
  • Serialized - When the number of requested parallel queries is downgraded to one, the query is no longer a parallel query but a serial query. The query has been serialized.
  • Not downgraded - When the specified number of parallel queries is performed as requested, the queries have not been downgraded.

Grids - Parallel Query Information

Page | Grid Description
Sessions | Parallel Query Sessions The columns in the table are identical to those in the Top Sessions Page, but cover only parallel query sessions, not all sessions.
Queue | Parallel Execution Queue

Note: Applies only to Oracle 11g Release 2.

Shows details of the sessions in the parallel execution queue, including the status of each session.


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