# 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).

## Timestamps in log files

From version 7.1 of Transformer, the resolution of log-event timestamps has been increased from millisecond to microsecond granularity. This aligns Transformer with the trend within the financial industry towards the use of higher-resolution timestamps. For more information, see [Timestamp resolution](../datasource/datasource-timestamp-resolution.md).

## Event log

The standard DataSource event log.

**Default file name**: `transformer.log`

**Configuration items**: [`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.

**Default file name**: `packet-transformer.log`

**Configuration items**: [`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

Pipeline message log.

**Default file name**: `pipeline.log`

**Configuration items**: [`logfile`](transformer-pipeline-configuration.md#logfile), [`log-level`](transformer-pipeline-configuration.md#log-level), [`pipeline-logflags`](transformer-pipeline-configuration.md#pipeline-logflags), and `add-pipeline:[log-flags](transformer-pipeline-configuration.md#log-flags)` in [Pipeline configuration](transformer-pipeline-configuration.md).

## Cluster log

The Cluster module’s log.

**Default file name**: `cluster.log`

**Configuration items**: [`logfile`](transformer-clustering-configuration.md#logfile) and [`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.

**Default file name**: -

**Configuration items**: [`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

**Default file name**: `_java-module-name_.log`

**Configuration items**: [`module-logfile`](transformer-java-transformer-module-configuration.md#module-logfile) and [`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 size of thread queues are recorded.

**Default file name**: -

**Configuration items**: [`threads-queue-report-logfile`](transformer-pipeline-threads-configuration.md#threads-queue-report-logfile) and [`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.

**Default file name**: `persistence.log`

**Configuration items**: [`logfile`](transformer-persistence-configuration.md#logfile) and [`log-level`](transformer-persistence-configuration.md#log-level) in [Persistence configuration](transformer-persistence-configuration.md)

---

**See also:**

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