Caching Datasets

The caching layer feature in VulcanSQL allows you to leverage caching to improve the performance and efficiency of your API queries. With the {% cache %} tag, you can query results directly from the cache layer storage, reducing the need for repeated queries to the data source. Let's explore how to use this feature effectively.

Caching with DuckDB

To provide efficient caching functionality, VulcanSQL utilizes DuckDB as the underlying storage engine. This ensures high-performance caching and improves the overall query execution speed.

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Please note that in order to use the caching layer feature, you need to have the DuckDB extension installed. If you are using VulcanSQL CLI binary, the DuckDB extension is already pre-bundled, so no additional installation is required. However, if you are using VulcanSQL in a NodeJS project, make sure to install the DuckDB extension separately to enable the caching functionality.

First, you need to add the following configuration to vulcan.yaml.

vulcan.yaml

cache:
  type: parquet
  folderPath: tmp
  loader: duckdb

In the configuration, tmp means there will be a new folder called tmp in the root directory of the project you created.

Caching Query Results

To utilize the caching layer, you can enclose your SQL query inside the {% cache %} and {% endcache %} tags. For example:

dept.sql

{% cache %}
SELECT * FROM cache_departments
WHERE "name" = {{ context.params.name }};
{% endcache %}

This tag enables the query to fetch the result from the cache layer storage. You can define which queries are preloaded into the cache layer by specifying cache settings in the configuration file. Here's an example configuration:

dept.yaml

urlPath: /departments
profile: pg
cache:
  - cacheTableName: 'cache_departments' # The name of the table in the cache layer storage
    sql: 'SELECT * FROM departments' # The SQL query to preload into the cache layer
    profile: pg # The data source profile to use for the SQL query

In this configuration, the cache_departments table will be utilized within the {% cache %} tag.

Reusing Cached Results

VulcanSQL provides the ability to keep the query result from the cache layer in a variable, which can be reused in subsequent queries. For example:

dept.sql

-- The cached result is stored in the variable named "employee"
{% cache employee %}
SELECT * FROM cache_employees WHERE "id" = {{ context.params.id }};
{% endcache %}

-- The cached result can be reused in subsequent queries by referencing the variable name "employee"
SELECT * FROM departments WHERE "employee_id" = {{ employee.value()[0].id }};

By assigning the result of the {% cache %} tag to the employee variable, you can access its value in subsequent queries. This allows you to build complex queries by utilizing the cached results. Note that when the {% cache %} tag does not have a variable assigned, it retrieves the result directly from the cache builder.