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Don Burleson Blog 








Oracle 10g adaptive threshold & automated corrective actions

Oracle Database Tips by Donald Burleson

Ever since Oracle 9i first allowed you to create a self tuning database, I've been interested in automating Oracle tuning, essentially programming the adaptive threshold alert rules and corrective actions.  in my book "Creating a Self-Tuning Oracle Database" ($9.95) I discuss scripting automated tuning actions, and I have more elaborate scripts in my 10g tuning book.
I discuss exception (threshold) based tuning in my book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

Oracle OEM provides alert thresholds for all of the common metrics, but until 10g r2 you could not program automatic corrective actions.

One of my favorite features of Oracle 10g OEM is the ability to create thresholds for server metrics such as CPU and RAM consumption.  Prior to this functionality you had to write your own tools for performing Oracle threshold alerts and automated corrective actions.  Let's take a look at the new adaptive threshold monitoring in 10g release 2, and see how you can do it in earlier releases of Oracle.

Automatic adaptive threshold monitoring

To understand the adaptive threshold collection mechanism I recommend this outstanding article.  Also, the Oracle documentation on adaptive thresholds notes that the OEM interface has been enhanced to with more sophisticated threshold metrics, now allowing two ways to monitor exception thresholds for alerts:

  • Significance Level - This uses metric percentages to trigger the alert, e.g. alert when physical reads exceeds 95% of the threshold value.

  • Percentage of Maximum - Oracle alerts based on your pre-defined threshold number.

"Once metric baselines are defined, they can be used to establish alert thresholds that are statistically significant and adapt to expected variations across time. For example, you can define alert thresholds to be generated based on significance level, such as the HIGH significance level thresholds are values that occur 5 in 100 times.

Alternatively, you can generate thresholds based on a percentage of the maximum value observed within the baseline period. These can be used to generate alerts when performance metric values are observed to exceed normal peaks within that period."

This Oracle document explains adaptive thresholds in plain English and notes that the threshold will adjust according to database load:

"Adaptive baselines help to significantly improve the accuracy of performance alerting. The adaptive baselines allow for improved manageability since the thresholds adapt to changes in usage and load, and the thresholds do not need to be reconfigured with these changes in load patterns."

Here is a query to see the adaptive threshold values from the data dictionary:

   v$metricname                        metric,
   dbsnmparm.mgmt_bsln_statistics      stat,
   dbsnmparm.mgmt_bsln_threshold_parms parm,
   dbsnmparm.mgmt_bsln_datasources     ds,
   dbsnmparm.mgmt_bsln_baselines       b
   stat.bsln_guid = parm.bsln_guid
   parm.bsln_guid = b.bsln_guid
   parm.datasource_guid = ds.datasource_guid
   stat.datasource_guid = ds.datasource_guid
   ds.metric_id = n.metric_id;

It's important to remember that this adaptive threshold alert functionality has been around since the earliest days of Oracle and it's good to see that it has finally been placed into OEM.  Here are my notes on exception threshold based Oracle tuning:

Here we see some of the metrics allowed for adaptive threshold monitoring in 10g r2, small, but it's a start:

When setting the adaptive thresholds you can choose the time period and the time grouping.  The larger the time grouping, the less granularity:

I first publishing about the display of metric signatures by hour-of-the-day and day-of-the-week in my book "High Performance Oracle tuning with STATSPACK", and I'm glad to see that signature analysis has been incorporated into the Oracle engine.

Many DBA's prefer to use the Ion tool for this type of predictive modeling because it is more mature and robust than OEM:

Just like Ion, Oracle 10g release 2 OEM now allows you to display your adaptive threshold metrics over time, in a more primitive method:

This ability to view repeating signatures is an extremely valuable proactive Oracle tuning technique.  Here are my notes on proactive signature analysis:

Corrective Actions in Oracle 10g release 2

The Oracle documentation states that Oracle is moving toward a full self-tuning database, with automatic corrective actions being triggers when the threshold is exceeded.  However the corrective actions are brand new, and I have scripts for creating a self-tuning database in my book "Creating a Self-Tuning Oracle Database" (only $9.95) with enhanced details on adaptive threshold monitoring and automatic corrective actions in my 10g Tuning book.  My notes on automated corrective actions describe the various methods for automating Oracle tuning.

If you want to learn more and get my working Oracle threshold monitoring scripts, see my book "Oracle Tuning: The Definitive Reference", over 900 pages of my favorite tuning tips & scripts. 





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