# Logging

Transformer can log many aspects of its operation, to help you check that it’s running correctly and pinpoint the source of any problems arising.

Because Transformer is a [DataSource application](../datasource/index.md), it comes with the standard [DataSource logging facilities](../datasource/datasource-logging-in-datasource-applications.md) built-in. It also produces a number of subsidiary logs that are dedicated to particular [Transformer modules](transformer-transformer-modules.md).

Here’s a summary of all the log files that Transformer can create, with links to the configuration items that define the log files and control the amount of detail logged.

| Log type | Default log filename | Related configuration items |
| --- | --- | --- |
| **Event log** The standard DataSource event log | `transformer.log` | [`event-log`](../datasource/datasource-logging-configuration.md#event-log) [`log-level`](../datasource/datasource-logging-configuration.md#log-level) [`add-log`](../datasource/datasource-logging-configuration.md#add-log) and others in [DataSource Logging configuration](../datasource/datasource-logging-configuration.md). |
| **Packet log** The standard DataSource packet log | `packet-transformer.log` | [`datasrc-pkt-log`](../datasource/datasource-datasource-peers-configuration-part-2.md#datasrc-pkt-log) in [DataSource peers configuration (part 2)](../datasource/datasource-datasource-peers-configuration-part-2.md) |
| **Pipeline activity log** The log file in which pipeline messages are recorded. | `pipeline.log` | [`logfile`](transformer-pipeline-configuration.md#logfile) [`log-level`](transformer-pipeline-configuration.md#log-level) [`pipeline-logflags`](transformer-pipeline-configuration.md#pipeline-logflags) [`add-pipeline`](transformer-pipeline-configuration.md#add-pipeline): [`log-flags`](transformer-pipeline-configuration.md#log-flags) in [Pipeline configuration](transformer-pipeline-configuration.md). |
| **Cluster log** The Cluster module’s log | `cluster.log` | [`logfile`](transformer-clustering-configuration.md#logfile) [`log-level`](transformer-clustering-configuration.md#log-level) in [Clustering configuration](transformer-clustering-configuration.md) |
| **Cluster packet log** The log file in which message packets passed between a Transformer and other nodes in the Transformer cluster are recorded. | (none) | [`cluster-packet-logfile`](transformer-clustering-configuration.md#cluster-packet-logfile) in [Clustering configuration](transformer-clustering-configuration.md) |
| **Java module log** One log file is produced for each Java module loaded into Transformer | `<Java-module-name>.log` For example, `jtm.log` | [`module-logfile`](transformer-java-transformer-module-configuration.md#module-logfile) [`log-level`](transformer-java-transformer-module-configuration.md#log-level) in [Java Transformer Module configuration](transformer-java-transformer-module-configuration.md) |
| **Thread queue sizes log** The log file in which the sizes of the thread queues are recorded. | (none) | [`threads-queue-report-logfile`](transformer-pipeline-threads-configuration.md#threads-queue-report-logfile) [`threads-queue-report-period`](transformer-pipeline-threads-configuration.md#threads-queue-report-period) in [Pipeline threads configuration](transformer-pipeline-threads-configuration.md) |
| **Persistence event log** The log file in which events about persisting data are recorded. | `persistence.log` | [`logfile`](transformer-persistence-configuration.md#logfile) [`log-level`](transformer-persistence-configuration.md#log-level) in [Persistence configuration](transformer-persistence-configuration.md) |

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**See also:**

* [Logging in DataSource applications](../datasource/datasource-logging-in-datasource-applications.md)