About logging

On top of NLog, ETLBox offers you support to create a simple but still powerful database logging, which is simple to set up and eays to maintain.


By default, ETLBox uses NLog. NLog already comes with different log targets that be configured either via your app.config or programmatically. See the NLog-documentation for a full reference: nlog-project.org   .

ETLBox already comes with NLog as dependency - so the necessary packages will be retrieved from nuget automatically through your package manager.

A simple Configuration File

In order to use logging, you have to create a nlog.config file (with this exact name) and put it into the root folder of your project. Make sure that it is copied into your output directory.

A simple and very basic nlog.config would look like this

      xsi:schemaLocation="NLog NLog.xsd"
    <target name="console" xsi:type="Console" />     

After adding a file with this configuration, you will already get some logging output to your console output when you trigger some ETLBox components.

Copy to output directory

Make sure the config file is copied into the output directory where you build executables are dropped. Your project configuration file .csproj should contain something like this:

  <None Update="nlog.config">

Debugging logging issues

NLog normally behaves very “fault-tolerant”. By default, if something is not setup properly or does not work when NLog tries to log, it just “stops” working without throwing an exception or stopping the execution. This behavior is very desirable in a production environment, but hard to debug.

If you need to debug Nlog, you can change the nlog root-element of the nlog.config into:

      xsi:schemaLocation="NLog NLog.xsd"

With this configuration it will raise an exception and also log it into a file.

Logging into files

Nlog can be easily configured to have your logging output stored in files. Here is an example for a simple configuration that will create a Log - folder within your application directory and have a file for every error level provided by Nlog. (NLog does differentiate each log entry by a log level, which are: Trace, Debug, Info, Warn, Error and Fatal.)

      xsi:schemaLocation="NLog NLog.xsd"
    <target name="file" xsi:type="AsyncWrapper"
      <target xsi:type="File" fileName="${basedir}/logs/${level}.txt"
              layout="${longdate}|${pad:padding=10:fixedLength=true:inner=${etllog:LogType=STAGE}}|${pad:padding=20:fixedLength=true:inner=${etllog:LogType=Type}}|${pad:padding=5:fixedLength=true:inner=${etllog:LogType=Action}}|${etllog}" />
    <logger name="*" minlevel="Debug" writeTo="file" />

As you can see, the log output into the file is formatted using a particular NLog notation in the Layout attribute. NLog does provide some default LayoutRenderer here. Additionally, ETLBox will register also some layout renderer which can be used. These are:

//The default log message of the component or task:

//The current value defined in Logging.Stage:

//The class name of the task or component that produces the log output:

 //A component can can produce more than on log message.
 //Actions can be 'START' (first log message), 'END' (component finished), 'RUN', 'LOG':

 //The hash value of the specific task or component, derived from the type and the name

//If a load process was started, the load process id is in here
layout="${etllog:LogType=LoadProcessKey}" />

The details for each layout renderer will explained in more details in the following chapters.

Setting the logging stage

One thing you perhaps want to know in your logging output is the current stage of your data processing. Think you this as a category for your log output - if things happen during the setup of your database, the Stage could be “SETUP” - if you are currently staging your data from your sources into your database the stage could be “STAGING”.

To set up or modify the current stage, just change the static property Stage in the Logging class:

Logging.STAGE = "SETUP"
//some logging

Disable logging

Perhaps you want some particular tasks or components not to produce any log output, but you don’t want to remove the logging completely. For this case you can use the DisableLogging property on every task or component in ETLBox. E.g., if you create a new DbSource, just set the property to true:

DbSource source = new DbSource("TableName") { DisableLogging = true};

If you want to disable logging in general for all tasks, you can set the static property DisableAllLogging in the ControlFlow class:

ControlFlow.DisableAllLogging = true;

Whenever set to true, no logging output will be produced. When set back to false, logging will be activated again.

Logging to database

Of course logging to console output or to a file is perhaps not sufficient. If you want to have logging tables in your database, ETLBox comes with some additions to the default logging mechanism provided by NLog.

Method 1: Extend the nlog.config

One way to have logging into the database enabled is to extend the nlog configuration and add your database as target. This way is the most flexible one, but it involves some manual steps: You have to set up the logging table yourself, and define the database target in your nlog.config file.

The modification to the nlog.config could like this:

      xsi:schemaLocation="NLog NLog.xsd"
    <target xsi:type="Database" name="database"
       useTransactions="false" keepConnection="true">
        INSERT INTO etllog (LogDate, Level, Stage, Message, TaskType, TaskAction, TaskHash, Source)
        SELECT @LogDate, @Level, @Stage, @Message, @Type, @Action, @Hash, @Logger
      <parameter name="@LogDate" layout="${date:format=yyyy-MM-ddTHH\:mm\:ss.fff}" />
      <parameter name="@Level" layout="${level}" />
      <parameter name="@Stage" layout="${etllog:LogType=Stage}" />
      <parameter name="@Message" layout="${etllog}" />
      <parameter name="@Type" layout="${etllog:LogType=Type}" />
      <parameter name="@Action" layout="${etllog:LogType=Action}" />
      <parameter name="@Hash" layout="${etllog:LogType=Hash}" />
    <logger name="*" minlevel="Info" writeTo="database" />

Method 2: Let ETLBox do the work

Alternatively, you can use some pre-defined Logging tasks to update your nlog configuration and create the logging table.

The following code snipped will do this for you:

var SqlConnectionManager connection = new SqlConnectionManager("Data Source=.;Integrated Security=SSPI;Initial Catalog=ETLBox_Logging");

In this example, CreateLogTableTask will create a logging table. The table structure will look like this:

Column nameData typeRemarks
load_process_idInt64Id of etlbox_loadproces table

This will work on all supported database - the real data type will be reflected by the corresponding database specific type. E.g. Int64 is a BIGINT on SqlServer and INTEGER on SqlLite The id column is an Identity (or auto increment) column, and the only one not nullable.

The AddLoggingDatabaseToConfig method will add the corresponding nlog database target to the nlog configuration. This happens to the configuration that Nlog keeps after reading the nlog.config file - the file itself will be untouched.

Now, if you call any task or component that creates log output, it will automatically be logged to the newly create database table

Log table name

By default, the name for the logging table is “etlbox_log”. If you want to change that name, the CreateLogTableTask and AddLoggingDatabaseToConfig method do have a parameter logTableName that can be set to your specifig table name. If you use a different name, before you call AddLoggingDatabaseToConfig you have to set the table name in the static property LogTable of ControlFlow class.

ControlFlow.LogTable = "mylogtable";
ControlFlow.AddLoggingDatabaseToConfig(connection, NLog.LogLevel.Debug, "mylogtable");

Also, when using the AddLoggingDatabaseToConfig, you can define a min log level at which Nlog start to produce log output. By default it is set to LogLevel “Info”.

Log output

After you added a log table (or all other nlog target like file or console output), all log message generated from any control flow task or data flow component will be redirected to this target.

The following example will create 4 rows in your log table. Every time a tasks or component starts, it will create a log entry with an action ‘START’. When it’s done with its execution, it will create another log entry with action type ‘END’

SqlTask.ExecuteNonQuery("some sql", "Select 1 as test");
Sequence.Execute("some custom code", () => { });

If you want to produce your own log output, you can use the LogTask. This will create only one row in your log output, with the TaskAction “LOG”. The message here would be “Some warning!”.

LogTask.Warn("Some warning!");

Also you can define the nlog level with the log task. E.g.:_

LogTask.Trace("Some text!");
LogTask.Debug("Some text!");
LogTask.Info("Some text!");
LogTask.Warn("Some text!");
LogTask.Error("Some text!");
LogTask.Fatal("Some text!");

Logging of Load Processes

Additionally to the traditional nlog setup where log information is send to any target by changing the configuration, ETLBox comes with a set of Tasks to control your ETL processes - so called “Load processes”.

The use case for a load process table is simple - if you have one log table, this table will store a log messages for an ETL job. If the job run again, more or less the same log information is written in the log table - with different timestamps of course. If you need to identify which log entry relates to which job run, there are some information missing. This is where the load process table comes in.

You can use the task CreateLoadProcessTableTask to have ETLBox created a load process table.


By default this will create a table “etlbox_loadprocess”. This table will look like this:

Column nameData typeRemarks
is_runningInt160 or 1
was_successfulInt160 or 1
was_abortedInt160 or 1

The table will contain information about the ETL processes that you started in your code with the StartLoadProcessTask. To end or abort a process, there is the EndLoadProcessTask or AbortLoadProcessTask.

Let’s look at the following example for logging into the load process table.

StartLoadProcessTask.Start("Process 1", "Starting process");

try {
/* ... some tasks or data flow */
   EndLoadProcessTask.End("The process ended successfully");
} catch (Exception e) {

After calling the StartLoadProcessTask a new entry was created in the etlbox_loadprocess table. This entry had a start date and contained the process name “Process 1” and the start message “Starting process”. The column is_running is 0. Calling the EndLoadProcessTask will set an end date and change the columns is_running to 0 and was_successful to 1. Vice versa will AbortLoadProcessTask set is_running to 0 and was_aborted to 1. The abort message would contain the exception as string.

When the load process entry is added to the table, a new id is created. All information about the load process (including the id) can be accessed via the static property CurrentLoadProcess in the ControlFlow class. Whenever a new log message for the log table is created, this entry will also contain the id of the current load process in the column load_process_id.

LogTask.Warn("This will create a log message")
Console.WriteLine("The log message will contain the current load process id: ControlFlow.CurrentLoadProcess.Id");

Whenever you end a process and start a new one, the CurrentLoadProcess property will switch to the current load process.

Load process table name

When you create the load process table, and you don’t pass a custom table name, by default the name of the table is “etlbox_loadprocess”. You can change this by passing the table name to the CreateLoadProcessTableTask. If the table is already created, you must specify the Table name in the static property LoadProcessTable of the ControlFlow class

//Will set the ControlFlow.CurrentLoadProcess property automatically:
CreateLoadProcessTableTask.Create(SqlConnection, "myloadprocesstable");
//If CreateLoadProcessTableTask was not executed:
ControlFlow.CurrentLoadProcess = "myloadprocesstable";

Further log tasks

There are some more logging tasks that can be used to manage your log tables.

Get log and loadprocess table in JSON

If you want to get the content of the etl.LoadProcess table or etl.Log in JSON-Format, there are two tasks for that:

var jsonLoadProcesses = GetLoadProcessAsJSONTask.GetJSON();
var jsonLog = GetLogAsJSONTask.GetJSON();

Reading log and load process table programmatically

If you want to read the load process programmatically, you can use the ReadLoadProcessTableTask. For accessing the log table, there is the ReadLogTableTask

//Get last aborted load process and read log entries
LoadProcess lastaborted = ReadLoadProcessTableTask.ReadWithOption(ReadOptions.ReadLastAborted);
List<LogEntry> allLogEntrieForLoadProcess = ReadLogTableTask.Read(connection, lastaborted.Id);

//Get all load processes and all log entries
List<LoadProcess> allLoadProcesses = ReadLoadProcessTableTask.ReadAll();
List<LogEntry> allLogEntries = ReadLogTableTask.Read(connection);