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Overview

This Snap provides the functionality of SCD (Slowly Changing Dimension) Type 2 on a target Snowflake table. You can use this Snap to execute one SQL lookup request per set of input documents to avoid making a request for every input record. Its output is typically a stream of documents for the Snowflake - Bulk Upsert Snap, which updates or inserts rows into the target table. Therefore, this Snap must be connected to the Snowflake - Bulk Upsert Snap to accomplish the complete SCD2 functionality.

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Snap Type

The Snowflake SCD2 is a Read-type Snap that enables you to execute multiple queries as a single atomic unit.

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Works in Ultra Pipelines. However, we recommend that you not use this Snap in an Ultra Pipeline.

Known Issues

Because of performance issues, all Snowflake Snaps now ignore the Cancel queued queries when pipeline is stopped or if it fails option for Manage Queued Queries, even when selected. Snaps behave as though the default Continue to execute queued queries when the Pipeline is stopped or if it fails option were selected.



We plan to address this issue in a patch for the next monthly release in December.

Snap Views

Type

Format

Number of Views

Examples of Upstream and Downstream Snaps

Description

Input 

Document

  • Min: 1

  • Max: 1

  • Mapper

  • JSON Parser Snap

A document in the input view should contain a data map of key-value entries. The input data must contain data in the Natural Key (primary key) and Cause-historization fields. 

Output

Document

  • Min: 1

  • Max: 1

  • Snowflake Bulk Upsert

A document in the output view contains a data map of key-value entries for all fields of a row in the target Snowflake table.

Error

Error handling is a generic way to handle errors without losing data or failing the Snap execution. You can handle the errors that the Snap might encounter while running the Pipeline by choosing one of the following options from the When errors occur list under the Views tab. The available options are:

  • Stop Pipeline Execution: Stops the current pipeline execution when the Snap encounters an error.

  • Discard Error Data and Continue: Ignores the error, discards that record, and continues with the rest of the records.

  • Route Error Data to Error View: Routes the error data to an error view without stopping the Snap execution.

Learn more about Error handling in Pipelines.

Snap Settings

Info

  • Asterisk (*): Indicates a mandatory field.

  • Suggestion icon ((blue star)): Indicates a list that is dynamically populated based on the configuration.

  • Expression icon ((blue star)): Indicates whether the value is an expression (if enabled) or a static value (if disabled). Learn more about Using Expressions in SnapLogic.

  • Add icon ((blue star)): Indicates that you can add fields in the field set.

  • Remove icon ((blue star)): Indicates that you can remove fields from the field set.

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Field Name

Field Type

Description

Label*

Default Value: Snowflake - SCD2
Example: Snowflake - SCD2

String

Specify the name for the Snap. You can modify this to be more specific, especially if you have more than one of the same Snap in your pipeline.

Schema name

Default Value: N/A 
Example: TestSchema

String/Expression

Specify the database schema name. In case it is not defined, then the suggestion for the Table Name will retrieve all tables names of all schemas. The property is suggestible and will retrieve available database schemas during suggest values.

Table Name

Default Value: N/A 
Example: TestTable

String/Expression

Specify the name of the table in the instance. The table name is suggestible and requires an account setting.  

The target table should have the following three columns for field historization to work:

  • Column to demarcate whether a row is a current row or not. For example, "CURRENT_ROW". For the current row, the value would be true or 1. For the historical row, the value would be false or 0.

  • Column to denote the starting date of the current row. For example, "START_DATE".

  • Column to denote when the row was historized. For example, "END_DATE". For the active row, it's null. For a historical row, it has the value that indicates it was effective till that date.

Use the ALTER table command to add these columns to your target table if they are not present. 

Natural key*

Default Value: N/A
Example: id (Each record has to have a unique value)

String/Expression

Specify the names of fields that identify a unique row in the target table. The identity key cannot be used as the Natural key, since a current row and its historical rows cannot have the same natural key value

Cause-historization fields 

Default Value: N/A
Example: gold bullion rate

String/Expression

Specify the names of fields where any change in value causes the historization of an existing row and the insertion of a new current row.

SCD fields

The historical and updated information for the Cause-historization field. Click + to add SCD fields. By default, there are four rows in this field-set:

  • Current row

  • Historical row

  • Start date of the current row

  • End date of historical row.

Meaning*

Default Value: 

  • Current row

  • Historical row

  • Start date of current row

  • End date of historical row

Dropdown list

Specifies the table columns that are to be updated for implementing the SCD2 type transformation.

Field*

Default Value: N/A
Example: CURRENT_ROW

String/Expression

Specify the fields in the table will contain the historical information. 

Below are the values that must be configured for each row:

  • Current row: The name of the column in the target table that holds the flag for the historized field. For example, "CURRENT_ROW".

  • Historical row: The name of the column in the target table that holds the flag for the historized field. It has to be the same as the value configured for the Current row field. For example, "CURRENT_ROW".

  • Start date of current row: The name of the column in the target table for denoting the start date for the current row. For example, "START_DATE".

  • End date of historical row: The name of the column in the target table for denoting the end date for the historical row. For example, "END_DATE".

By default, the start and end date for both Current row and Historical row are null. After the Snap is executed, the start date for the updated row data automatically becomes the end date for the earlier version of the data (Historical row).

Value*

Default Value: 

  • Current row and Historical row: N/A

  • Start date of current row, and End date of historical row: Date.now()

String/Expression

Specify the value to be assigned to the current or historical row. For date-related rows, the default is Date.now(). 

The Value field should be configured as follows:

  • Current row: 1

  • Historical row: 0

Ignore unchanged rows

Default value: Deselected

Checkbox

Specifies whether the Snap must ignore writing unchanged rows from the source table to the target table. If you enable this option, the Snap generates a corresponding document in the target only if the Cause-historization column in the source row is changed. Else, the Snap does not generate any corresponding document in the target. 

Number of Retries

Default Value: 0
Example: 3

Integer/Expression

The number of times that the Snap must try to write the fields in case of an error during processing. An error is displayed if the maximum number of tries has been reached.

Retry Interval (Seconds)

Default Value: 1
Example: 3

Integer/Expression

The time interval, in seconds, between subsequent retry attempts. 

Auto Historization Query

This field-set is used to specify the fields that are to be used to historize table data. Historization is in the sort order specified. Care must be taken that the field is sortable. You can also add multiple fields here; historizaton occurs when even of the fields is changed. 

Field*

Default Value: N/A
Example: Invoice_Number

String/Expression

Specify the name of the field. This is a suggestible field and suggests all the fields in the target table.

If this field has null values in the incoming records, then the value in the Snowflake table is treated as the current value and the incoming record is historized. 

Sort Order*

Default Value: Ascending Order
Example: Descending Order

Dropdown list

The order in which the selected field is to be historized. Available options are:

  • Ascending Order: The higher value is classified as a current event. For example date of transaction, age, height, etc.

  • Descending Order: The lower value is classified as the current event. For example, rank.

Input Date Format

Default Value: Continue to execute the snap with given input Date format
Example: Auto Convert the format to Snowflake default format

Dropdown list

The property has the following two options:

  • Select Continue to execute the snap with the given input Date format if you want the Snap to continue with the current date format. This option is selected by default. 

  • Select Auto Convert the format to Snowflake default format if you want the Snap to convert the provided date format to the default Snowflake date format. To know about the date formats supported by Snowflake, see Snowflake date formats

Manage Queued Queries

Default Value: Continue to execute queued queries when the Pipeline is stopped or if it fails
Example: Cancel queued queries when the Pipeline is stopped or if it fails

Dropdown list

Select this property to decide whether the Snap should continue or cancel the execution of the queued Snowflake Execute SQL queries when you stop the pipeline.

If you select Cancel queued queries when pipeline is stopped or if it fails, then the read queries under execution are canceled, whereas the write queries under execution are not canceled. Snowflake internally determines which queries are safe to be canceled and cancels those queries.

Snap Execution

Default Value: Validate & Execute
Example: Execute only

Dropdown list

Multiexcerpt include macro

Select one of the following three modes in which the Snap executes:

  • Validate & Execute: Performs limited execution of the Snap, and generates a data preview during Pipeline validation. Subsequently, performs full execution of the Snap (unlimited records) during Pipeline runtime.

  • Execute only: Performs full execution of the Snap during Pipeline execution without generating preview data.

  • Disabled: Disables the Snap and all Snaps that are downstream from it.

Examples

Historizing Incoming Records

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This Pipeline performs the following operations:

Info

The Target Table

Before we start, let us look at the target table and understand some of its columns that are necessary for the Pipeline:Image Removed

Image Added

We focus on the highlighted columns above to demonstrate auto-historization and describe their function in the table.

  • POINT ID is the natural key in this table.

  • Changes in SCHEDULEDVOLUME for a natural key are historized.

  • HISTORYSTARTDATE and HISTORYENDDATE are used to identify the current record. 

  • FLAG denotes if a record is a current record with the value TRUE.

  • STARTDATE and ENDDATE are automatically calculated by the Snap. They represent the date range during which a record was the current record. The ENDDATE is blank for the current record.

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