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Saturday, December 13, 2008

Graphing AWR Data in Excel

I often use data collected by the Oracle Automatic Workload Repository (AWR) to help to diagnose performance problems. However, I often work on performance problems with application teams, rather than the DBAs.  It is surprising how often that I don't have access to Oracle Enterprise Manager.

Somebody might say that the system was slow at a particular time. I want to get an overview of the database at that time, and I might also want to compare it to another time when the system wasn't slow. Later I may generate AWR reports using particular pairs of snapshots, but I need something to direct me to when an issue occurred, and hence which snapshots to compare.

When dealing with performance problems the question is nearly always the same. "How long did I spend doing what?". Amongst lots of metrics, AWR collects snapshots of how much time system-wide has been spent waiting on each wait event.

Thumbnail of AWR wait chartTo give me an overview of that data, I have created an excel spreadsheet that will query the AWR repository and retrieve that data for up to a week into am Excel pivot table, and will then graph the top wait events. Click on the thumbnail on the left to see an example.

For me, this approach has a number of advantages:

  • First; don't drown in numbers. The eye is very good at picking out patterns and irregularities. You can then drill into the numbers behind the chart.
  • The chart provides a quick overview of the behaviour of the database. You can quickly see if there is anything to examine in more detail, or whether the database is exhibiting its normal characteristics.
  • The AWR data is extracted into the spreadsheet, so I can keep a copy of the spreadsheet for reference. I generally like to collect AWR snapshots every 15 minutes. One week of data, at that frequency, turns into about 6Mb of spreadsheet.
  • Excel charts can easily be put into documents, presentations or e-mails. Excel is very flexible, it is easy to format the chart to show only what is important.
  • It's free (that is to say that you won't need to go and buy anything else). All you need is Excel and an Oracle client.
Over time I have produced a variety of spreadsheets that collect all sorts of metrics from the Oracle database and others that collect specific metrics from PeopleSoft applications.

To be fair, AWR's forerunner, Statspack collects a lot of similar data to AWR, the essential difference being that AWR is a licensed option. This technique could also be used to extract data from the statspack repository, but most of my customers are licensed for AWR.

You can download a sample Excel workbook and query from my website. Go to one of the sheets with data and 'Refresh Data'. The first time you will probably be prompted to select and ODBC source. You will be prompted for the login credentials.

In a subsequent blog posting I will discuss a real example of where this technique helped me to resolve a problem.

It is fairly straightforward to create spreadsheets that query databases, but here are some links that should help to get you going if you are not familiar with the process.
  • From the Microsoft website: 'Use Microsoft Query to retrieve external data'. This is based on Excel 2007, but it explains how Excel calls MSQuery which then calls the ODBC driver. However, I recommend that you do not use the Query Wizard. I prefer to get the query working in SQL*Plus and then I copy it into MSQuery
  • Querying External Data in Excel. This is a straightforward recipe for using MSQuery.
Update 16.6.2010: I have released a new version with an adjustment to the query used in the spreadsheet.  AWR snapshots happen at slightly different times on different RAC nodes, although they have the same SNAP_ID.  This was causing multiple rows for the same snapshot in the pivot tables, and so the charts did not show correctly aggregated wait events across RAC nodes.

4 comments:

David Kurtz said...

For an example of that takes this idea much further see Tanel Poder's blog: Core IT for geeks and pros: Advanced Oracle Troubleshooting @OOW 2008 presentation slidesand scripts

abbottdba said...

Fantastic idea. Sifting through piles of data is much easier graphically. Thanks for this example and idea.

JP said...

This is exactly what I'm trying to do. I am unable to locate the sample spreadsheet you are talking about in your blog. Can you provide it?

David Kurtz said...

The link in the posting is correct - the spreadsheet is in the awr_wait.zip file on the scripts page of the Go-Faster website.