S3 Load Generator (Snowflake)
S3 Load Generator is a tool that helps users load delimited data from public objects in an S3 Bucket (Amazon Simple Storage Service).
Unlike common components, the Load Generator does not appear as a standalone component when dragged onto the job canvas. Instead, the Load Generator takes the form of a tool that allows users to load and view files on the fly, altering load component properties and observing their effects without the need for a separate Transformation job. The generator can also guess the schema of a table, relieving much of the end user's work.
Note: This component requires working AWS Credentials with "read" access to the bucket that contains the source data's file(s). This is easily achieved by attaching an IAM role to the instance when launching Matillion ETL for Snowflake; however, it can also be managed by editing an Environment. See the example at the bottom of this article.
Furthermore, Matillion requires use of a policy that contains the s3:ListBucket action, such as the policy provided in the Managing Credentials documentation.
Note: Clicking on any of the images in this article will enlarge the image for readability.
When a user drags the S3 Load Generator onto the canvas, a three-page setup wizard appears (see the below images).
A file must first be selected from an S3 bucket. This file must be delimited (including .csv) and the user must have permission to access the file. If the file is compressed, the correct compression method must be selected; supported compression methods are gzip and bzip2.
If the selected file is viable, users can select the number of rows they wish to sample and click the Get Sample button. Here, the tool will load the file's data and attempt to guess its schema. Raw data for the file is displayed in the large panel below.
On page 2, column data is displayed in the lower-right panel and is available for editing. Schema configuration properties for the table are displayed in the lower-left panel; the available properties are detailed in the below table (article section "Properties").
Selecting the Guess Schema button will order the Load Generator to attempt to guess as many of these properties as possible. However, all of the properties are available for manual editing by the user, as is the column data in the lower-right panel.
When the user is satisfied with the settings, the resulting table output can be viewed by selecting the 'Test' button at the bottom of page 3 of the setup wizard. Running a test will create the requested table on the Snowflake cluster and show a sample for the user to inspect. If the user is unhappy with the output, they can return to the 'Configuration' panel on page 2 to make alterations until they are satisfied with the result.
|For more information on all the settings in this component, see the Snowflake COPY syntax for more information.|
|Table Name||Text||The descriptive name for the table.|
|Field Delimiter||Text||The Field Delimiter is a character that separates fields in an input file. The default is a Comma (,). A [TAB] character can be specified as "\ ".|
|Field Optionally Enclosed By||Text||Character used to enclose strings. Value can be:
NONEsingle quote character ('); or a double quote character (").
When a field contains this character, escape it using the same character.
|Ignore Header Rows||Text||The number of rows at the top of the file to ignore - defaults to 0.|
|Date Format||Text||Defaults to 'auto' - this can be used to manually specify a date format.|
|Time Format||Text||Defaults to 'auto' - this can be used to manually specify a time format.|
|Time Stamp Format||Text||Defaults to 'auto' - defines the format of timestamp values in the data files to be loaded.|
|Escape Unenclosed||Text||Single character string used as the escape character for unenclosed field values only. Default is backslash (\\).|
|Escape||Text||Single character used as the escape character for any field values.|
|Null As||Text||This option replaces the specified string with null in the output table. Use this if your data has a particular representation of missing data.|
|Trim Blanks||Checkbox||If this is enabled, Matillion ETL removes trailing and leading whitespace from the input data.|
|Error on Column Count||Checkbox||If enabled, a parsing error is generated when the number of delimited columns (fields) in the input data file does not match the number of columns in the corresponding table.|
|Empty As Null||Checkbox||If this is set, empty columns in the input file will become NULL.|
In the following example, the S3 Load Generator is used to load the contents of a small file into a table. First, the Load Generator is given the path to the file, and since the file is not compressed, we keep the Compression setting set to "None". After taking a sample of the data, the large panel displays raw data from the file (up to the number of lines specified by the 'Row Limit', and we can see that this dataset is a list of US states and their airport codes, delimited by white space.
On page 2, clicking 'Guess Schema' will enable the S3 Load Generator to autocomplete the properties for this file. In the properties panel (lower left panel), the Load Generator has identified the whitespaces as tabs.
However, in the lower-right panel, we can see that only one column of our two-column dataset has been guessed by the wizard.
On the final page of the setup wizard, clicking the 'Test' button returns an error to our example. Although the data appears to be delimited correctly, we have already identified that our problem is with the column names. Load Generator has guessed (incorrectly in this particular case) only one column name, and also not provided the correct name. Now is our chance to go back through the wizard and make the necessary corrections.
To correct the problems, we simply return to the Guess Schema section of the wizard, and add a second column by clicking the + button. We should take a moment here to double check that the 'Ignore Header Rows' parameter is set to 0, meaning we assume that the file has no header rows at all, so that we can create them manually. Next, in the lower-right panel, we select each field under 'Name' and name the two columns something more appropriate. In this case, we have a column called "state" and a column called "airport code".
Returning to the Test, the S3 Load Generator will update the sample table with our new properties. Our test result provides us with a sample two-column table, just like we wanted. The columns are labelled appropriately and we can now go on to use this table with other Matillion ETL for Snowflake AWS jobs and components.
Clicking 'OK' will return users to the job interface and create two linked components: Create/Replace Table and Load. Each component is parameterised by the S3 Load Generator and can be run as a job by linking to a Start component.