Hydrolix Spark Connector: Microsoft Fabric Deployment

Overview

Microsoft Fabric is an end-to-end data platform that unifies data engineering, data science, real-time analytics, and business intelligence under one SaaS offering. With the help of the Hydrolix Spark Connector, you can improve query speed and storage costs of your Fabric-deployed Spark cluster by using Hydrolix as the backing store.

Requirements

Prerequisites

• Hydrolix Cluster: A running Hydrolix cluster version 4.22.1 or higher. Deployment instructions for your preferred cloud vendor (AWS, Google, Linode, or Microsoft) can be found here.
• Fabric Spark Cluster: A Microsoft Fabric account with a deployed Spark cluster.

Microsoft Requirements

Required User Permissions

Querying your Hydrolix bucket via Spark requires the same permissions as querying via your cluster. Specifically, a user needs the following permissions at the levels indicated:

If you will be querying multiple tables within the same Hydrolix project, it's easier to scope those permissions to the project level instead of granting the permissions for each table.

Setup Steps

1. Create a Summary Table of the Data You Will Be Querying
2. Create and configure a Workspace

At which point you can start querying your data using Spark.

Create a Summary Table of the Data You Will Be Querying

Create a summary table, including a transform, of the data you will be querying. This aggregates the queriable data, reducing query time. Instructions for creating a summary table via the Hydrolix UI and API are on the Summary Tables page. While this step can be skipped, it is highly recommended.

The general structure of summary transforms and their limitations are explained in this section on creating summary transforms.

Create and configure a workspace

A workspace in MS Fabric is a collaborative environment where users can create, manage, and share data, reports, dashboards, and other analytics assets. The following steps walk you through the process of creating and configuring a workspace to query Hydrolix data with the Hydrolix Spark Connector using python notebooks.

To create a new workspace, follow these steps.

1. Open the Capacity created in a previous step. Verify that it's running.
2. Navigate to Microsoft Fabric.
3. In the left-hand panel, select Workspaces > + New workspace.
4. Fill in a name for the new workspace.
5. Under License mode, select Fabric Capacity and choose the created capacity from the available options.
6. Save the workspace.
7. Open your created workspace.
8. Select Workspace settings > Data Engineering/Science > Spark settings > Environment.
9. Enable Set default environment then select Workspace default > New environment.

10. Provide a custom name for the new environment. The new environment settings will open immediately after creation.
11. Navigate to Custom Library and upload the Spark Connector JAR file.

12. Navigate to Spark properties and configure the connection to your Hydrolix cluster using the following properties.

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Spark configuration is dynamically reloaded for every query.

The Spark Connector reloads its configuration for every query. To change the configuration inside spark-shell or a Jupyter notebook, set spark.conf.set("some_setting", "value").

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Verify user permissions.

Make sure the user supplied within the spark properties has the required permissions for the underlying Hydrolix cluster.

13. Save and Publish your Spark configurations. Wait until the publishing process is complete.
14. Return to your workspace, select the newly created environment as your default environment, and select Save.
15. Add a new item by selecting + New item > Notebook in your workspace.
16. Run a simple query from the Notebook to test the connection.

query = """SELECT app, avg(num_partitions) FROM hydrolix.hydro.logs WHERE app in ('query-peer', 'query-head', 'intake-head', 'intake-peer')
and timestamp >= '2025-01-17 12:00:00' AND timestamp < '2025-01-18 12:00:00' GROUP BY app""""
df = spark.sql(query)
df.show(10, truncate=False)

Querying

After you have configured your cluster, you can use the Hydrolix Spark Connector in a Spark notebook.

To begin using the connector with a Spark notebook, you’ll use one of the two commands depending on your use case:

• Python or Scala fragment: sql("use hydrolix")
• SQL fragment: use hydrolix;

Alternatively, you can prepend each table you want to query from your Hydrolix Back-End with hydrolix..

Summary table query instructions

Summary table queries have unique requirements.

1. Wrap summary aliases in SELECT statements with hdxagg(). For example, you might run the following to query both an aliased column (summary_column_alias) and a non-summary column (non_summary_column).

SELECT hdxAgg('summary_column_alias'), non_summary_column 
FROM hydrolix.project.summary_table 
GROUP BY {time_field_alias}

You can read more creating and querying summary tables in the Summary Tables documentation.

The hdxAgg() function resolves name conflicts between summary table alias columns and spark function names. For example, count may be a column name in a summary table, but count() is also a pre-existing spark function. Using the hdxAgg() function disambiguates the two.

The hdxAgg() function also resolves name conflicts between multiple summary tables. For example, one summary table might have count(timestamp) AS total in its definition while another might have count(distinct username) AS total in its definition. The hdxAgg() function disambiguates total() and ensures it works when querying either table.

2. Load the Hydrolix datasource. Doing so loads the required hdxAgg() function. The options for loading the Hydrolix datasource are:

• Run use hydrolix
• Run any query against a non-summary table
• Run io.hydrolix.connectors.spark.HdxUdfRegistry.enableSummaryTables(spark)

(v1.0.0 only) Summary table query instructions

The v1.0.0 release of the Hydrolix Spark Connector has unique instructions for querying summary tables.

1. To enable querying the summary table you created during the Create a Summary Table step, run the following line in a Spark shell or in a PySpark session:

io.hydrolix.connectors.spark.HdxUdfRegistry.registerSummaryTable(spark, "{project.summary_table_name}")

2. Reference any summary table column aliases using the following syntax: summary_column_alias(). For example, suppose there is a summary table called my_project.my_summary_table which includes the following in its definition:

SELECT ...
sum(salary) AS totalSalary,
department,
...

This table can then queried with:

SELECT totalSalary(), department FROM hydrolix.my_project.my_summary_table GROUP BY department

Troubleshooting

Authentication Error

If you see "access denied" errors from the Hydrolix database when you are making queries, ensure the cluster username and password are correct, and make sure that user has query permissions.

User Permissions

Partitions in a table might be distributed across different storage buckets.

If the user set in your Spark Connector configuration doesn't have the required permissions for querying all the storage buckets via the ClickHouse JDBC Driver, the cluster will be unable to sign partitions from a storage bucket for the table. This will result in the query failing and returning an error response.

Error querying summary tables

If a user sees this error:

org.apache.spark.sql.AnalysisException: [UNRESOLVED_ROUTINE] Cannot resolve function `hdxAgg` on search path [`system`.`builtin`, `system`.`session`, `spark_catalog`.`default`]

The fix is to load the Hydrolix datasource. You can do so by doing any one of the following:

• Run io.hydrolix.connectors.spark.HdxUdfRegistry.enableSummaryTables(spark). This performs a global setup step which creates the hdxAgg function.
• Run the use hydrolix fragment. This directly loads the Hydrolix datasource.
• Run any query against a non-summary table. This directly loads the Hydrolix datasource.

Limitations

Read-only

The Hydrolix Spark Connector is read-only. ALTER and INSERT statements aren't supported.