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Oracle Real Application Testing (RAT) – Part 2: What is Capture & how to do it ?

Posted by FatDBA on February 10, 2020

Hi Folks,

Continuing the same subject/topic what I have started in my last post – Real Application Testing (RAT). This post is all about the ‘Capture‘ part what happens on the source database where we captures the workload which will later on replayed on the target database.

I have break it in to few easy steps to understand.

Step 1:
First we need to verify if the RAT option is installed and working fine. This you only need to verify upto 10Gr2 as all later versions comes with all features enabled by himself during the installation process, until you didn’t de-selected any specific feature during customized installation.
In case of 10g you need to check using v$option dynamic view for RAT parameter and there is a need to enable the parameter ‘pre_11g_enable_capture’.

Please see below the steps of verification!

Step 2:
Creating exclusion FILTERS (If Required) for capture.
This is the step where we create filters to exclude few of the system usernames and few of other schemas like SYSMAN, SYS and all of such schemas where you don’t want to capture load.
Please see the screenshot use to do the same.

Step 3:
Creation of RAT specific OS based directory.
This is the place where all CAPTURE files will be saved and should be created like below.

Step 4:
Next, we can now start the CAPTURE process, this should be done using the main RAT specific procedure DBMS_WORKLOAD_CAPTURE and its function START_CAPTURE. Here the main parameter to pass is name (Name of the capture you want to name), dir (directory which will hold all workload files, the same what I have created above).
There are few parameters which I have intentionally not used i.e. DURATION as there is a BUG in 10Gr2 database which causes the capture not to stop even after specific time and had to manually stop the process. So in below example I will be capturing XXXXX minutes of load from this database and will stop it explicitly.

This being a staging setup I am taking around 30 minutes of workload but in real time this could be anything between 10 or 15 minutes of peak hours.

You can monitor the progress using DBA_WORKLOAD_CAPTURES view. See below.

Next, you can get more details about this ongoing capture activity. See below.

Step 5:
Next when we are done with the capturing of load for the specified time, we can go and stop it now. In my case on RS staging I left that running and capturing workload for ~ 32 Minutes.

Next, you can verify the contents by going to the RAT directory. There you will see .rec (recording) files, .wmd and a special report (TEXT/HTML format) will generate and is specific to CAPTURE process only.

Now we have BEGIN SNAP Id and END SNAP (time duration for the capture runtime) we can generate the AWR report as well.
The same report can be fetched via text method as well.

Step 6:
Next we will export the AWR data. This will be later on used to generate the comparison report from REPLAY side. This will create two more files under the capture directory wcr_ca.log and wcr_ca.dmp

Next steps starts at the target end or the host and deserves a separate post.
I will soon be writing about Replay process in my next post. Till that time keep learning!

Hope It Helps
Prashant Dixit

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