Troubleshooting Aggregators Module | MuleSoft Documentation
# Troubleshooting Aggregators Module
To troubleshoot the Aggregators module, become familiar with the information about app logs, enabling verbose logging, and interpreting commonly thrown messages.
## Use the Latest Aggregators Module Version
To ensure that you use the latest patches, update the Aggregator module to the latest version. In the Apache Maven `pom.xml` file generated by Anypoint Studio, replace `x.x.x` with the version that corresponds to the latest version:
```
<dependency>
 <groupId>org.mule.modules</groupId>
 <artifactId>mule-aggregators-module</artifactId>
 <version>x.x.x</version>
 <classifier>mule-plugin</classifier>
</dependency>
```

To obtain the most up-to-date `pom.xml` file information:
  1. Go to Anypoint Exchange.
  2. In Exchange, click **Login** and supply your Anypoint Platform username and password.
  3. In Exchange, search for `aggregators`.
  4. Select the connector.
  5. Click **Dependency Snippets** near the upper right of the screen.


## Enable Verbose Logging
To begin troubleshooting Aggregator module, enable verbose logging to see the exact error messages:
  1. Access Anypoint Studio and navigate to the **Package Explorer** view.
  2. Open your application’s project.
  3. Open the `src/main/resources` path folder.
  4. Open the `log4j2.xml` file inside the folder.
  5. If the following line is already in the `log4j2.xml` file, uncomment it to enable it; otherwise, add it:
```
<AsyncLogger name="org.mule.extension.aggregator" level="DEBUG"/>
```

  6. Save your changes.
  7. Click the project name in **Package Explorer** and then click **Run** > **Run As** > **Mule Application**.
  8. Navigate to the **Console** view to read the messages in the logger.


## Understand the Timeout Behavior in the Size-Based Aggregator
For the **Size based aggregator** scope, the **Timeout** field indicates the maximum time to wait for the aggregation to complete. If the timeout is reached before the total number of elements is equal to the value set in the **Max size** field, the aggregation is not considered complete and the aggregation is reset. Note that you can use an **Aggregator listener** source to capture the elements that were aggregated before the timeout occurred. For further details on timeout behavior, see how to configure the Size-Based Aggregator Timeout and Max Size Fields documentation.
## Make Sure You Are Not in a Multiple Worker Setting
Aggregators don’t work with multiple workers and a persistent object store because clustering is not available in CloudHub. For details on how workers can be shared or doubled to scale your application and provide high availability, see the CloudHub Fabric documentation.
## Understand Common Throws
Here is a list of common throw messages and how to interpret them:
For **Size based aggregator** :
  * AGGREGATORS:AGGREGATOR_CONFIG
```
The Max size or Timeout fields have invalid values, for example, Max size < 0.
```

  * AGGREGATORS:OBJECT_STORE_ACCESS
```
An error occurred during an attempt to access the object store used to store the aggregated values.
```



For **Time based aggregator** :
  * AGGREGATORS:AGGREGATOR_CONFIG
```
The Period or Max size fields have invalid values, for example, Period = 0.
```

  * AGGREGATORS:OBJECT_STORE_ACCESS
```
An error occurred during an attempt to access the object store used to store the aggregated values.
```



For **Group based aggregator** :
  * AGGREGATORS:GROUP_COMPLETED
```
An error occurred during an attempt to add a new element to an already completed group that was not yet evicted.
```

  * AGGREGATORS:GROUP_TIMED_OUT
```
An error occurred during an attempt to add a new element to a group that timed out but had not yet been evicted.
```

  * AGGREGATORS:NO_GROUP_ID
```
The expression that resolves to the group ID returns null.
```

  * AGGREGATORS:NO_GROUP_SIZE
```
The expression that resolves to the group size returns null.
```

  * AGGREGATORS:AGGREGATOR_CONFIG
```
The Group size or Timeout fields have invalid values, for example, groupSize < 0.
```

  * AGGREGATORS:OBJECT_STORE_ACCESS
```
An error occurred during an attempt to access the object store used to store the aggregated values.
```



## See Also
  * Aggregators Module Reference
  * MuleSoft Help Center
  *