Incremental loading allows an organization to only load the most recent transactional data into their data warehouse and staging databases, in order to facilitate faster load times. This can be beneficial when the volume of transactional data in the data source causes scheduled execution times to take longer than desired. Incremental loading can also help facilitate more reasonable execution times when multiple updates throughout the day are desirable.
Full Load Process
The default load plan during scheduled execution is a Full Load. During a full load all of the tables and fields that are used in a project are completely refreshed and the full data set is moved from the data source to the staging database and data warehouse. During the full load process, the existing tables in the staging database and data warehouse are truncated - which removes all of the existing data first and then the new data is subsequently loaded from the data source.
Incremental Load Process
During the incremental load process, the Jet Data Manager looks at fields that are defined by the user in order to automatically determine the amount of data that will be moved over. During the first deployment after incremental loading has been enabled, the Jet Data Manager will create additional tables in the staging database and data warehouse that have a _INCR suffix. The Jet Data Manager will then do a full load to bring over all of the required data from the data source. During subsequent execution of the project, truncation is disabled on these tables so that the original data is not removed. The Jet Data Manager then determines which records have been added to the data source since the last load and only transfers these new records to the appropriate tables in the staging database and data warehouse. This can drastically cut down on the amount of time necessary for execution of the objects in the project.
Does My Organization Need Incremental Loading Enabled?
A common misconception is that candidacy for incremental loading is directly dependent on the size of the data source (NAV, GP, AX, etc.). The best indicator as to whether or not incremental loading should be enabled is not the amount of data that needs to be transferred, but is actually the amount of time that it takes to transfer the data. Every organization has unique environments in which the Jet Data Manager is installed. One organization may experience an execution time of 30 minutes to transfer 50gb of data while another organization may experience only 10 minutes to transfer the same amount, or be able to transfer a much larger volume of transactional data in the same 30 minutes. Once the amount of time required to perform a full load begins to run longer than the organization feels is acceptable regarding their execution strategy (nightly updates, multiple updates throughout the day, etc.) then incremental loading becomes a viable option. If you are unsure as to whether incremental loading is a proper fit for your organization, you can contact our Jet Enterprise team by emailing firstname.lastname@example.org.
How to Enable Incremental Loading
The first step in setting up an incremental loading plan is to identify those tables which should have incremental loading enabled. Most smaller or summary level tables such as Customer, Item, and G/L Account tables will not generally impact performance, as they will not have a substantial number of records. The tables that are candidates to have incremental loading enabled will be larger transaction tables such as those that contain large volumes of general ledger and inventory transactions. The examples used in this document will use the G/L Entry table from Dynamics NAV, however the concepts are universal and apply to all data sources.
Enabling Incremental Loading for Staging Database Tables
To enable incremental loading for tables in the staging database, you will first need to go to the table in the staging database, right-click the table name, and select Table Settings.
On the Data Extraction tab, check the box for Enable source based incremental load. Click OK to continue.
If a red “X” denoting an error appears near the Physical Valid Table checkbox on the Performance tab, it means that this box must be checked in order to use incremental loading on this table. Check the box for Physical Valid Table prior to clicking OK.
The table icon in the staging database will now have an “I” icon identifying it as an incrementally loaded table.
Locate the table in the Data Source section at the bottom of the Data tab. Right-click the table name and select Add Incremental Selection Rule .
Check the box or boxes that mark the fields that will identify which records have been added or changed since the last incremental load. These will ideally be fields that are generated by the system and incremented sequentially when new records are added.
Repeat the steps above for all tables to which incremental loading will be enabled.
Right click the Business Unit and select Deploy and Execute -> Deploy and Execute Modified Object.
Click the Start button to initiate the first full load of the tables with source based incremental loading now enabled.
The necessary incremental tables will be automatically added to the staging database and populated with the latest incremental values. The next time that the table is executed, the Jet Data Manager will query these tables to determine the last record that was previously loaded and will only extract data from the data source that occurred since the last execution.
Using the Incremental Load Wizard
When you have more than a trivial amount of data in a table, incremental load becomes incredibly useful. While setting up incremental load for a single table is fast and easy, it can be a time-consuming task to implement in multiple tables. In Jet Data Manager 2017 and higher, you can set up incremental load for any number of tables in a wizard-style interface.
To access the wizard right click on the applicable data source, go to Automate, and select Set Up Incremental Load:
Select the tables you want to load incrementally, select primary key fields, and set your data selection rules. Jet Data Manager will then apply your selections. Combined with the easier application of primary key suggestions in JDM 2017 and higher, setting up incremental load in a large number of tables is a very simple process.
Enabling Incremental Loading for Data Warehouse Tables
In the staging database, right-click the table that you previously configured to use incremental loading. Navigate to Advanced → Show System Control Fields .
Notice that a series of system generated fields have been added to the bottom of the table.
Grab the DW_TimeStamp field and bring it to the table in the data warehouse where you wish to implement incremental loading. In this example, we moved the DW_TimeStamp field from the G/L Entry table to our Finance Transactions table.
In the data warehouse, right-click the table for which you wish to implement incremental and select Table Settings .
Check the box for Source based incremental load. Click OK .
Select the system generated timestamp field that we previously added to the table.
After you select the field to use in the incremental loading selection rule, you then need to make sure your data warehouse table has a primary key set. This will be indicated by a gold key. If your table does not have a primary key setup you will need to make one.
There are two options. Number one is to find out what the primary key for that table is in the data source and bring that field up into the data warehouse and then set it as the primary key.
The number two option would be to use the fields that already exist in the table. If there isn't a unique field on it's own in the table, you can set more than one field as a primary key and the combination of those fields will result in a unique ID.
To set a field as a primary key in the data warehouse, just right click on the field and choose "Include in Primary Key". The field will then have a little gold key on it. See below. Then you can Deploy and Execute without an error.
Right-click the data warehouse node and select Deploy and Execute -> Deploy and Execute Modified Objects .
If the table for which you are attempting to setup incremental loading has multiple data movements, you will need to add the system generated DW_TimeStamp field for each data movement associated with the table.
How to Implement Target Based Incremental Loading
Target based incremental loading is primarily used when there are no identifying fields that determine which records have been added since the last incremental update. With target based incremental loading, all of the data is moved over from the data source, the records are compared against the existing records in the table, and only new, updated, or deleted records are added to the staging database or data warehouse. Because of the method that needs to be used to handle these types of tables, target based incremental loading will not be as fast as source based incremental loading but will be faster than a full load strategy.
To enable target based incremental loading for a table, right-click the table name and select Table Settings .
Check the box for Target Based. Click OK.
The table icon will now have a “T” in it, identifying this table as one that has target based incremental loading enabled.
At the bottom of the list of fields for the table there is now an option for Incremental Settings.
Clicking on this will populate the target based incremental load selection window on the right-hand side of the screen.
The first pane represents the Target Based Incremental Keys. The field or fields that represent the primary key for the table should be checked.
The second pane represents the Target Based Value Keys. The Jet Data Manager will create a hash key field based on the field values for all of the fields selected in this window. This is what will be used to determine if a record has been updated. Check all of the fields that would represent a change in this table. In this example all fields have been selected.
The third pane represents the Incremental Events that the Jet Data Manager will take into consideration.
Inserts represent any new records that have been inserted, based on the primary key on the table.
Updates represent any records that have modified or been changed since the last incremental update. This is determined based on the Target Based Value Keys selected.
Deletes represent any records that previously existed in the data source but no longer exist, based on the primary key. These will be removed from the staging database or data warehouse table.
Right click on the table name and select Deploy and Execute to perform the initial load of the table.
Click the Start button to begin the deployment and execution process.
During this process, all of the data will be loaded and the hash keys for the target based incremental load will automatically be generated by the Jet Data Manager. Subsequent executions of the table will only load and process data cleansing operations on records that have been added, modified, or deleted from the data source since the last execution.
Handling of Deleted Records
If you use incremental load on a data source, and records are deleted, the tables in your data warehouse can quickly become out of sync with the data source. In versions of Jet Data Manager prior to v17.1, you handle this by scheduling a periodic full load of the table combined with (if necessary) a script to remove any records deleted in the data source on each incremental load. In Jet Data Manager 17.1 and higher, automated delete handling is available as an option on incrementally loaded tables.
To turn on Automated Delete Handling, right-click on the incrementally loaded table and select Table Settings, then go to the Date Extraction tab:
In addition to the traditional behavior (Don’t Handle Deletes), in v17.1 and higher, you can choose between two types: Hard deletes, where the records deleted in the data source are also deleted in the valid instance, and soft deletes, where the records are just marked as deleted in the valid instance. The feature is implemented as shown in the figure below:
On each incremental load, data is extracted from the source and into two instances of the table. The raw instance contains all the new records, while the primary key (“PK”) instance contains the content of the primary key columns for all records. Once the data has been transferred from raw to valid through the transformation view, Jet Data Manager will delete any record in the valid instance that has a primary key that cannot be found in either the raw or the PK instance. If soft delete is enabled, Jet Data Manager will add a column (“Is tombstone”) to the valid instance and updated deleted records with the value “true”.
The implementation is designed to be fast and simple. At the same time, it provides a good infrastructure to handle more advanced use cases. e.g.:
- If a record is undeleted/restored in the source, Jet Data Manager will not undelete it in the valid instance, unless it is loaded into the raw table again. So, depending on your situation, you could build a simple post script onto the data cleansing to raise the dead records with a simple update of the valid instance based on the PK instance.
- If a primary key is transformed from raw to valid, Jet Data Manager will not be able to match it to the primary keys stored in the raw and PK instance. If this transformation is to be taken into account when looking for deleted records, consider placing the transformation in a prescript. Sometimes, you might not know if you can expect records to be deleted in a data source; the new options make it easy to test. Simply enable soft deletes for the table and see if tomb stoned records begin to appear.