This topic explains what a diagnostic session is and how to capture diagnostic session on a transaction.
A diagnostic session captures detailed data about the processing of a transaction as transaction snapshots over a defined period of time. This data includes full call graphs.
Diagnostic sessions can be triggered manually through the user interface or configured to start automatically when thresholds for slow, stalled, or error transactions are reached. If the diagnostic session is triggered manually, the diagnostic session collects snapshots on all the nodes that the selected business transaction passes through. If the diagnostic session is triggered to start automatically, the diagnostics session collects snapshots on the triggering node.
Triggering a Diagnostic Session
You can manually trigger a diagnostic session when you need one or configure them to start up automatically.
On-demand Diagnostic Sessions
On-demand diagnostic sessions must be started manually.
To Start a Diagnostic Session for a Business Transaction Manually
1. Display the dashboard for the business transaction that you want to analyze. See Business Transactions List.
2. Click Actions -> Start Diagnostic Session or right-click on the selected business transaction and then click Start Diagnostic Session.
3. Specify the snapshot collection duration at the bottom of the Start Diagnostic Session window.
AppDynamics will start collecting transaction snapshots for that business transaction.
Automatic Diagnostic Sessions For Slow and Error Transactions
AppDynamics provides default thresholds to detect slow, very slow, stalled and error transactions. You can configure settings for triggering diagnostic sessions for these transactions.
To Configure Diagnostic Session Thresholds
1. In the left navigation pane, click Configure -> Slow Transaction Thresholds.
2. For configuring thresholds for business transactions click the User Transaction Thresholds tab. For thresholds for background tasks, click the Background Tasks Thresholds tab.
3. In the thresholds tree list, select the scope of the threshold, either:
- Default Thresholds
- Individual Transaction Thresholds
4. In the right panel configure thresholds for when diagnostic sessions will be started.
Here you can set a trigger based on the percentage of requests that exceed the Slow Request threshold. For performance reasons you may not want to trigger a diagnostic session each time a threshold is exceeded.
5. Configure diagnostic session duration and collection frequency. This includes:
- Number of snapshots to collect over a specified time period
- Number of unsuccessful attempts per minute
- Wait period between sessions
For performance reasons you want to limit the duration and frequency of diagnostic sessions to the minimum required time to obtain the maximum amount of information for troubleshooting purposes.
When there are ongoing performance problems you do not want a diagnostic session to run continuously. You can set a wait period between sessions and increase the time as needed.
Accessing a Diagnostic Session
You can access a diagnostic session from the transaction snapshot list.
To View a Diagnostic Session
1. Navigate to the transaction snapshot list.
See To View Transaction Snapshots.
2. Select a transaction snapshot from the list and either double-click it or click View Dashboard.
3. Click the Diagnostic Sessions tab.
4. From the list select a diagnostic sessions and click View Diagnostic Session.
From there you can double-click a transaction snapshot to dive deeper.