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Don Burleson Blog 







Oracle Monitoring Best Practices

Oracle Database Tips by Donald BurlesonJuly 20,  2015

All DBA's are required to set-up an Oracle monitoring infrastructure and the architecture of the monitoring system is directly dependent on the demands of management.  Oracle system cost the end-user community millions of dollars, and the end-user often demand service-level agreements (SLA's) that impose strict monitoring tasks for the Oracle professional.

In many shops, the end-user community is demanding Oracle performance statistics at a detailed level:

  • A financial services company demands that 95% of their Oracle transactions complete within one wallclock second.  The DBA most develop a monitoring strategy to ensure compliance. (Note:  there are special techniques that can be employed to get end-to-end response time within Oracle).
  • A stock brokerage demands that the DBA write a sophisticated real-time proactive monitor.  This monitor will quickly diagnose and pinpoint Oracle bottlenecks, but getting the data is a problem.  It requires real-time access to all internal Oracle control structures.  Running the monitor imposes a measurable burden on overall system load.
  • A manufacturing plant requires measuring response time by hour-of-the-day to ensure fast throughput for all shifts.

These are just a few examples of the business demands that drive the Oracle professional to create sophisticated monitoring infrastructures.  Let's example some of the most important issues when making these decisions.

The art of gathering Oracle performance data

There are several choices that need to be made when architecting an Oracle monitoring strategy:

  • Proactive or reactive monitoring? - Do we collect real-time data for crisis management, or collect time-series snapshots for predictive analytics?
  • Collect external statistics?  - Oracle does not run in a vacuum, and the speed of disk, network and CPU have a profound influence on overall response time.
  • What statistics? - Oracle provides hundreds of statistics that are cryptic and undocumented (i.e. calls to kcmgas), and you must decide what metrics are best suited to your business need.   For example, a requirement to measure end-to-end response time would benefit from monitoring network latency (SQL*Net Roundtrips), but only tangentially from monitoring data buffer cache efficiency.
  • What level of granularity? - What are the tradeoffs between super-details statistics and system performance?  How much data is required for a statistically significant sample size?
  • Build or Buy? - While the structures of Oracle performance collections are well documented, the Oracle professional needs to determine whether to purchase off-the-shelf Oracle monitoring tools or build their own custom interface.

A monitoring report for server-side metrics

So, where do we start?  Let's start with Oracle own metadata and cover these topics:

  • Inside Oracle's time-series monitoring infrastructure (AWR, STATSPACK and ASH)
  • Inside the Oracle v$ performance monitoring views
  • A review of extra cost monitoring tools and options
  • Building your own monitoring architecture

Inside Oracle's monitoring infrastructure

Oracle has already developed a great data collection infrastructure within the Automated Workload Repository (AWR) which is built-in to the Oracle kernel.  AWR snapshots will rarely impose any measurable system load and by default, Oracle collects AWR data in hourly snapshots for long periods of time (determined by the DBA).  To complement AWR, Oracle has created the Automated Session History data collection mechanism, which keeps highly-detailed session information for a short period of time (Usually an hour, or 30 minutes, as specified by the DBA).

Within the Oracle core software we see Oracle Corporation balance the issue of statistics detail and overall system performance with AWR (long term proactive) vs.  ASH (short-term reactive).   Oracle's own monitoring and statistics collection mechanisms (STATSPACK and AWR) are built to be very unobtrusive because they quickly extract snapshots of accumulators from the x$ fixed tables.

The real-time ASH table for Oracle monitoring

Using predictive analytics, the AWR and ASH data can be used to predict future outages and changes in performance, an important benefit for a DBA who must meet strict SLA requirements. 

Using linear regression with AWR data

Most Oracle professionals will monitor for several dozen metrics.  To get more information on AWR and ASH:

Inside Oracle's v$ performance views

The V$ views provide continually metrics at internal statistics. You may hear the V$ views called dynamic performance views or tables for this reason and there are over 150 of them.  The v$ views are created on top of Oracle x$ fixed tables (which are in-reality C structures) and you can see the mapping of the x$ tables to the v$ views by examining the v$ creation scripts in $ORACLE_HOME/rdbms/admin/catalog.sql.

The v$ data is similar to the AWR and ASH data in that they raw data are accumulators, measuring a metric since startup time. To make v$ information useful, it's helpful to take repeated samples over a fixed time period and compute the delta values.

A review of extra cost Oracle monitoring options & tools

Within the world of molecular physics, the scientists say that the act of observing a sub-atomic behavior will alter the behavior, and we see the same problem with Oracle system monitoring. In the nanosecond world of the CPU, the act of collecting statistics about a processing operation can easily exceed the cost of the instruction itself.

The same is true of some real-time monitors that sample SGA information directly from the SGA and other third party tools that use server-side agent processes to monitor Oracle.  Before you invest in real-time monitors, beware of several potential problems:

  • On stressed systems, greedy real-time monitors can create more performance problems than they reveal. 
  • There are few options to remedy an acute performance problem - It can be difficult if not impossible to correct some acute performance problems.

I personally recommend the following real-time Oracle monitors

  • Confio - Confio Ignite software is a low footprint tool that allow you to identify perforance issues in real time.
  • Oracle performance pack and diagnostic pack - While not best-of-breed, these tools are fully integrated with Oracle and fully supported by Oracle Corporation.

For proactive monitoring tools, there are several choices.  Because they use pre-collected data from STATSPACK and AWR, they impose no burden on the production system.  I personally endorse and sell these proactive Oracle monitors:

Building your own Oracle monitoring infrastructure

In the classic build vs. buy decision you must weigh the relative costs of developing a customized Oracle monitoring solution in-house vs. the time costs for the Oracle professional to cobble together a solution.  The relative benefits of each approach involve:

  • Build - You get the benefit of a customized solution that can be easily changed and enhanced, with customized alert mechanisms.  The downside is that they require significant knowledge for Oracle internals.  Sophisticated Oracle monitors can take hundreds of hours to develop.
  • Buy - Buying a tool has several advantages, foremost that you get quick access to performance data.  The downsides are the high costs and the difficulty in customizing the tool to meet the business monitoring requirements of your shop.

 In sum, Oracle monitoring addresses a critical business need to quality and response time assurance, and it is the challenge of the Oracle professional to leverage upon the performance data from the v$ views, and AWR/ASH tables to monitor and analyze important performance trends within Oracle.

Oracle Monitoring References:

See these related references on Oracle monitoring:




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