Getting Started with Snowflake

This getting started gives some clues to start working with Snowflake

Connect to your Data

The database structure can be entirely reversed in metadata and then used in mappings and processes to design and adapt the business rules to meet the user’s requirements.

You can refer to Connect to your Data page which explains the procedure.

Below is an example of reversed Snowflake metadata.

getting started snowflake metadata overview

Temporary Storage

Overview

To optimize data loading into Snowflake, Semarchy xDI uses a temporary storage location to store temporary files before loading them into Snowflake.

When necessary, source data is first extracted to temporary files which are sent into this temporary storage location, before being loaded into Snowflake using the dedicated Snowflake loaders.

Currently, Semarchy xDI supports the following storage locations:

  • Internal Snowflake Stage

  • External Storage

    • Microsoft Azure Storage

    • Amazon S3

Storage definition

The storage information is defined in the Snowflake metadata.

On the Snowflake metadata server node:

  1. Select the Storage tab.

  2. Define the Storage Method property.

  3. Define the External Storage property if you are using external storage.

  4. (Optional) Change the Compression Behavior.

getting started snowflake metadata storage overview

The following properties are available:

Property Description

Storage Method

Storage method used as default in mappings loading data into Snowflake.

  • internalStage: temporary files will be stored inside a Snowflake internal stage.

  • externalStorage: temporary files will be stored in an external storage system which must be defined using 'External Storage' attribute.

This will be the default method for all schemas and tables of this metadata.

External Storage

Metadata link of the external storage container to be used when using external storage method. Choose in the list the external storage, or drag and drop it inside the property.

This property supports: * A Microsoft Azure Storage Container * A Amazon S3 Folder.

Note that this will be the default for all the schemas and tables of this metadata.

Compression Type

Defines the compression type used when loading files (source files or temporarily generated files) into this database.

Compression Strategy

Defines the compression behavior when loading files (source files or temporarily generated files) into this database.

  • compress at execution: use this option when you want Semarchy xDI to compress files which are sent to Snowflake during flows automatically during execution. Template will use correct Snowflake options to specify compression type, compress the files using a Gzip Process Action, and then send compressed file to Snowflake.

  • delegate compression to driver: use this option when you want the compression of files which are sent to Snowflake during flows to be performed automatically by the Snowflake driver, using the 'AUTO_COMPRESS' option supported on the 'PUT' statement. Note that this is supported only when using Snowflake internal stage (see 'Storage Method' parameter')

  • assume already compressed: use this option when source files have already been compressed before the execution of mappings. Templates will use the correct Snowflake options to specify compression type and simply send them without compressing them as they are already compressed.

Those attributes can be overridden per schema and per table: for this, go on the desired schema or table node, then go inside the 'Storage' tab where you’ll find the same attributes, which will override the value set on the parent nodes.

Those attributes can also be overridden directly in mappings through parameters on Load Templates, allowing to manually define a different behavior than the one specified in metadata.
'External Storage' is not linked to the 'Storage Method'. You can decide to use 'internalStage' storage method but provide an External Storage link for specific cases where you’ll override the default storage method.

Definition of an external storage

As indicated in the above properties documentation, you can define the external storage location by selecting the related location, or by dragging and dropping it directly on the property.

To define an external storage, the prerequisite is to have the corresponding metadata existing in your workspace.

Example through a drag and drop:

getting started snowflake metadata storage external

Refer to Getting Started with Microsoft Azure Blob Storage and Amazon S3 to learn how to create this metadata.

Override of storage configuration

The storage configuration that is defined on the server node can be overridden on schema, on table, and directly in mappings.

This offers the ability to have a common default behavior and override it when it is required for some specific developments or use cases.

Example of an override on a schema node:

getting started snowflake metadata storage override

Example of an override in a mapping:

getting started snowflake mapping storage override

VARIANT Data Type

The VARIANT data type allows storing structured data such as JSON, AVRO, or XML.

Semarchy xDI supports reading data inside columns with this data type.

Reverse engineering of the data structure is also supported through the following procedure:

  1. In the Snowflake metadata, select the column with the VARIANT data type.

  2. Fill the Data Structure property with the JSON schema corresponding to the structure of data contained in the column.

    Use the […​] button that is close to the Data Structure property to open a wizard that helps fill this property. The wizard has different options to generate the JSON schema from a sample of data, files, and more…​

  3. Right-click the column, select Actions, then Reverse Datastructure.

  • Only the JSON format is currently supported.

  • The structure under the VARIANT column can be used as source only in mappings, to read JSON data.

Create your first mappings

Your metadata is ready and your tables reverse engineered, you can now create your first mappings.

The Snowflake technology can be used like any other database in Semarchy xDI.

Drag and drop your sources and targets, map the columns as usual, and configure the templates accordingly to your requirements.

Loading data from a database into Snowflake

getting started snowflake mapping example 1

Loading data from a Delimited File into Snowflake

getting started snowflake mapping example 2

Loading data from Snowflake into another database

getting started snowflake mapping example 3

Performing Reject detection while loading a Snowflake Table

getting started snowflake mapping example 4

Loading structured data contained in a VARIANT field into another database

getting started snowflake mapping example 5 semi structured

The warnings on the target fields are displayed because of the hierarchical structure that is currently unknown by the expression parser. They can be ignored.

Replicating a source database into Snowflake

getting started snowflake process example 1

Sample Project

The Snowflake Component ships sample project(s) that contain various examples and use cases.

You can have a look at these projects to find samples and examples describing how to use it.

Refer to Install Components to learn how to import sample projects.