# Presto

## Prerequisites

- The hostname for the [Presto][presto] database server
- The username/password for the [Presto][presto] database server
- The name of the database to use within the [Presto][presto] database server

## Setup

### Manual

Add the following to a `.env` file in your Cube project:

```dotenv
CUBEJS_DB_TYPE=prestodb
CUBEJS_DB_HOST=my.presto.host
CUBEJS_DB_USER=presto_user
CUBEJS_DB_PASS=**********
CUBEJS_DB_PRESTO_CATALOG=my_presto_catalog
CUBEJS_DB_SCHEMA=my_presto_schema
```

## Environment Variables

| Environment Variable       | Description                                                                         | Possible Values                               | Required |
| -------------------------- | ----------------------------------------------------------------------------------- | --------------------------------------------- | :------: |
| <EnvVar>CUBEJS_DB_HOST</EnvVar>           | The host URL for a database                                                         | A valid database host URL                     |    ✅    |
| <EnvVar>CUBEJS_DB_PORT</EnvVar>           | The port for the database connection                                                | A valid port number                           |    ❌    |
| <EnvVar>CUBEJS_DB_USER</EnvVar>           | The username used to connect to the database                                        | A valid database username                     |    ✅    |
| <EnvVar>CUBEJS_DB_PASS</EnvVar>           | The password used to connect to the database                                        | A valid database password                     |    ✅    |
| <EnvVar>CUBEJS_DB_PRESTO_CATALOG</EnvVar> | The catalog within Presto to connect to                                             | A valid catalog name within a Presto database |    ✅    |
| <EnvVar>CUBEJS_DB_PRESTO_AUTH_TOKEN</EnvVar> | The authentication token to use when connecting to Presto/Trino. It will be sent in the `Authorization` header. | A valid authentication token |    ❌    |
| <EnvVar>CUBEJS_DB_SCHEMA</EnvVar>         | The schema within the database to connect to                                        | A valid schema name within a Presto database  |    ✅    |
| <EnvVar>CUBEJS_DB_SSL</EnvVar>            | If `true`, enables SSL encryption for database connections from Cube                | `true`, `false`                               |    ❌    |
| <EnvVar>CUBEJS_DB_MAX_POOL</EnvVar>       | The maximum number of concurrent database connections to pool. Default is `8`       | A valid number                                |    ❌    |
| <EnvVar>CUBEJS_CONCURRENCY</EnvVar> | The number of [concurrent queries][ref-data-source-concurrency] to the data source | A valid number |    ❌    |
| <EnvVar>CUBEJS_DB_EXPORT_BUCKET_TYPE</EnvVar> | The export bucket type for pre-aggregations | `s3`, `gcs` | ❌ |
| <EnvVar>CUBEJS_DB_EXPORT_BUCKET</EnvVar> | The export bucket to connect to | A valid bucket URL | ❌ |
| <EnvVar>CUBEJS_DB_EXPORT_BUCKET_AWS_KEY</EnvVar> | The AWS Access Key ID to use for export bucket writes | A valid AWS Access Key ID | ❌ |
| <EnvVar>CUBEJS_DB_EXPORT_BUCKET_AWS_SECRET</EnvVar> | The AWS Secret Access Key to use for export bucket writes | A valid AWS Secret Access Key | ❌ |
| <EnvVar>CUBEJS_DB_EXPORT_BUCKET_AWS_REGION</EnvVar> | The AWS region to use for export bucket writes | A valid AWS region | ❌ |
| <EnvVar>CUBEJS_DB_EXPORT_GCS_CREDENTIALS</EnvVar> | A Base64 encoded JSON key file for connecting to Google Cloud Storage | A valid Google Cloud JSON key file, encoded as a Base64 string | ❌ |

[ref-data-source-concurrency]: /product/configuration/concurrency#data-source-concurrency

## Pre-Aggregation Feature Support

### count_distinct_approx

Measures of type
[`count_distinct_approx`][ref-schema-ref-types-formats-countdistinctapprox] can
be used in pre-aggregations when using Presto as a source database. To learn
more about Presto support for approximate aggregate functions, [click
here][presto-docs-approx-agg-fns].

## Pre-Aggregation Build Strategies

<InfoBox>

To learn more about pre-aggregation build strategies, [head
here][ref-caching-using-preaggs-build-strats].

</InfoBox>

| Feature       | Works with read-only mode? | Is default? |
| ------------- | :------------------------: | :---------: |
| Simple        |             ✅             |     ✅      |
| Export Bucket |             ❌             |     ❌      |

By default, Presto uses a [simple][self-preaggs-simple] strategy to
build pre-aggregations.

### Simple

No extra configuration is required to configure simple pre-aggregation builds
for Presto.

### Export Bucket

Presto supports using both [AWS S3][aws-s3] and [Google Cloud Storage][google-cloud-storage] for export bucket functionality.

#### AWS S3

<InfoBox>

Ensure the AWS credentials are correctly configured in IAM to allow reads and
writes to the export bucket in S3.

</InfoBox>

```dotenv
CUBEJS_DB_EXPORT_BUCKET_TYPE=s3
CUBEJS_DB_EXPORT_BUCKET=my.bucket.on.s3
CUBEJS_DB_EXPORT_BUCKET_AWS_KEY=<AWS_KEY>
CUBEJS_DB_EXPORT_BUCKET_AWS_SECRET=<AWS_SECRET>
CUBEJS_DB_EXPORT_BUCKET_AWS_REGION=<AWS_REGION>
```

#### Google Cloud Storage

<InfoBox>

When using an export bucket, remember to assign the **Storage Object Admin**
role to your Google Cloud credentials (<EnvVar>CUBEJS_DB_EXPORT_GCS_CREDENTIALS</EnvVar>).

</InfoBox>

```dotenv
CUBEJS_DB_EXPORT_BUCKET=gs://presto-export-bucket
CUBEJS_DB_EXPORT_BUCKET_TYPE=gcs
CUBEJS_DB_EXPORT_GCS_CREDENTIALS=<BASE64_ENCODED_SERVICE_CREDENTIALS_JSON>
```

## SSL

To enable SSL-encrypted connections between Cube and Presto, set the
<EnvVar>CUBEJS_DB_SSL</EnvVar> environment variable to `true`. For more information on how to
configure custom certificates, please check out [Enable SSL Connections to the
Database][ref-recipe-enable-ssl].

[aws-s3]: https://aws.amazon.com/s3/
[google-cloud-storage]: https://cloud.google.com/storage
[presto]: https://prestodb.io/
[presto-docs-approx-agg-fns]:
  https://prestodb.io/docs/current/functions/aggregate.html
[ref-caching-using-preaggs-build-strats]:
  /product/caching/using-pre-aggregations#pre-aggregation-build-strategies
[ref-recipe-enable-ssl]:
  /product/configuration/recipes/using-ssl-connections-to-data-source
[ref-schema-ref-types-formats-countdistinctapprox]: /product/data-modeling/reference/types-and-formats#count_distinct_approx
[self-preaggs-simple]: #simple
