# Logging

{% hint style="warning" %}

#### Workshop - Logging

Use logging to diagnose transformation problems. Create a controlled type mismatch error. Use log level and output to find the cause.

**What you’ll do**

* Change field metadata to trigger an error
* Run with **Basic** and **Row level** logging
* Use **Execution results** to find the failing step
* Locate the same error in `pdi.log`

**Prerequisites:** Complete the **Hello World** workshop

**Estimated time:** 5 minutes
{% endhint %}

{% embed url="<https://www.loom.com/share/868c1e73bdeb464e9ef5c2dd3c220d61?hideEmbedTopBar=true&hide_owner=true&hide_share=true&hide_title=true>" %}
Logging
{% endembed %}

***

{% hint style="info" %}
**Create a new transformation**

Use any of these options to open a new transformation tab:

* Select **File** > **New** > **Transformation**
* Use `Ctrl+N` (Windows/Linux) or `Cmd+N` (macOS)
  {% endhint %}

<figure><img src="/files/loS5a4lF51rXARcNKI8Z" alt="" width="375"><figcaption><p>Logging</p></figcaption></figure>

{% file src="/files/mkALCJT1B7bbbTJUrbOb" %}

{% tabs %}
{% tab title="1. Modify Generate Rows" %}
{% hint style="info" %}
Start from the transformation you built in **Hello World**.
{% endhint %}

{% hint style="info" %}

#### **Generate Rows**

Generate Rows is a test-data step. It is a quick way to validate logging and error handling.
{% endhint %}

{% hint style="warning" %}
To create an error, change the field type for `message` from **String** to **Integer**.
{% endhint %}

1. Double-click the **Generate Rows** step.
2. Change the type for `message` to **Integer**.

<div align="center"><figure><img src="/files/Za4qHHAeBcKbC0di993V" alt="" width="375"><figcaption><p>Change data type</p></figcaption></figure></div>

3. Select **OK**.
   {% endtab %}

{% tab title="2. Run" %}
{% hint style="info" %}

#### Run the transformation

Run with a higher log level to see row-level detail.
{% endhint %}

1. Select **Run** in the canvas toolbar.
2. Set **Log level** to **Basic**.
3. Select **Run**.
4. Run again with **Log level** set to **Row level**.

<div align="center"><figure><img src="/files/WdjoimzUF2XWYEo4UPwu" alt="" width="563"><figcaption><p>Set row level debugging</p></figcaption></figure></div>

5. Select **Run**. The failing step is highlighted.

<figure><img src="/files/LDApRREPhxV1kUh5ZkZ7" alt="" width="375"><figcaption><p>Error in step</p></figcaption></figure>

6. In **Execution results**, open the **Log** tab.

<figure><img src="/files/Vm6XnlJlsWboa4ioPCIZ" alt=""><figcaption><p>Logging - error</p></figcaption></figure>

The error text is in the log output. Look for the first **ERROR** entry.

{% hint style="info" %}
Tip: Select the minus icon to show errors only.

The same error is written to `pdi.log`:

{% tabs %}
{% tab title="Windows" %}
`C:\\Pentaho\\design-tools\\data-integration\\logs\\pdi.log`
{% endtab %}

{% tab title="macOS / Linux" %}
`~/Pentaho/design-tools/data-integration/logs/pdi.log`
{% endtab %}
{% endtabs %}
{% endhint %}

<figure><img src="/files/EOgcXcFs3DF8LMUO1GFs" alt=""><figcaption><p>pdi.log - Linux</p></figcaption></figure>
{% endtab %}
{% endtabs %}

***

Next workshop: [Error Handling](/pentaho-data-integration/data-integration/concepts-and-terminology/error-handling.md)


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