# Considerations with Presto on Amazon EMR
<a name="emr-presto-considerations"></a>

Consider the following limitations when you run [Presto](https://aws.amazon.com/big-data/what-is-presto/) on Amazon EMR.

## Presto command line executable
<a name="emr-presto-command-line-cli"></a>

In Amazon EMR, PrestoDB and Trino both use the same command line executable, `presto-cli`, as in the following example.

```
presto-cli --catalog hive
```

## Non-configurable Presto deployment properties
<a name="emr-presto-deployment-config"></a>

The version of Amazon EMR that you use determines the Presto deployment configurations that are available. For more information about these configuration properties, see [Deploying Presto](https://prestodb.io/docs/current/installation/deployment.html) in the Presto documentation. The following table shows the different configuration options for Presto `properties` files.


| File | Configurable | 
| --- | --- | 
|  `log.properties`  |  PrestoDB: Configurable in Amazon EMR versions 4.0.0 and later. Use the `presto-log` configuration classification.  | 
|  `config.properties`  |  PrestoDB: Configurable in Amazon EMR versions 4.0.0 and later. Use the `presto-config` configuration classification.  | 
|  `hive.properties`  |  PrestoDB: Configurable in Amazon EMR versions 4.1.0 and later. Use the `presto-connector-hive` configuration classification.  | 
|  `node.properties`  |  PrestoDB: Configurable in Amazon EMR version 5.6.0 and later. Use the `presto-node` configuration classification.  | 
|  `jvm.config`  |  Not configurable.  | 

## PrestoDB installation
<a name="emr-prestodb-prestosql"></a>

The application name *Presto* continues to be used to install PrestoDB on clusters. 

You can install either PrestoDB or Trino, but you can't install both on a single cluster. If you specify both PrestoDB and Trino when you attempt to create a cluster, a validation error occurs and the cluster creation request fails.

## EMRFS and PrestoS3FileSystem configuration
<a name="emr-presto-prestos3"></a>

With Amazon EMR versions 5.12.0 and later, PrestoDB can use EMRFS. For more information, see [EMR File System (EMRFS)](https://docs.aws.amazon.com/emr/latest/ReleaseGuide/emr-fs) in the *Amazon EMR Management Guide*. With earlier versions of Amazon EMR, PrestoS3FileSystem is the only configuration option.

You can use a security configuration to set up encryption for EMRFS data in Amazon S3. You can also use IAM roles for EMRFS requests to Amazon S3. For more information, see [Understanding encryption options](https://docs.aws.amazon.com/emr/latest/ManagementGuide/emr-data-encryption-options.html) and [Configure IAM roles for EMRFS requests to Amazon S3](https://docs.aws.amazon.com/emr/latest/ManagementGuide/emr-emrfs-iam-roles.html) in the *Amazon EMR Management Guide*.

**Note**  
If you query underlying data in Amazon S3 with Amazon EMR version 5.12.0, Presto errors can occur. This is because Presto fails to pick up configuration classification values from `emrfs-site.xml`. As a workaround, create an `emrfs` subdirectory under `usr/lib/presto/plugin/hive-hadoop2/` and create a symlink in `usr/lib/presto/plugin/hive-hadoop2/emrfs` to the existing `/usr/share/aws/emr/emrfs/conf/emrfs-site.xml` file. Then restart the presto-server process (`sudo presto-server stop` followed by `sudo presto-server start`). 

You can override the EMRFS default and use the PrestoS3FileSystem instead. To do this, use the `presto-connector-hive` configuration classification to set `hive.s3-file-system-type` to `PRESTO` as shown in the following example. For more information, see [Configure applications](emr-configure-apps.md).

```
[
   {
      "Classification": "presto-connector-hive",
      "Properties": {
         "hive.s3-file-system-type": "PRESTO"
      }
   }
]
```

If you use PrestoS3FileSystem, use the `presto-connector-hive` configuration classification to configure PrestoS3FileSystem properties. For more information about available properties, see [Amazon S3 configuration](https://prestodb.io/docs/current/connector/hive.html#amazon-s3-configuration) in the Hive Connector section of the Presto documentation. These settings do not apply to EMRFS.

## Default setting for end user impersonation
<a name="emr-presto-end-user-impersonation"></a>

By default, Amazon EMR versions 5.12.0 and later enable end user impersonation for access to HDFS. For more information, see [End user impersonation](https://prestodb.io/docs/current/connector/hive-security.html#end-user-impersonation) in the Presto documentation. To change this setting with the `presto-config` configuration classification, set the `hive.hdfs.impersonation.enabled` property to `false`.

## Default port for Presto web interface
<a name="emr-presto-default-web-port"></a>

By default, Amazon EMR configures the Presto web interface on the Presto coordinator to use port 8889 (for PrestoDB and Trino). To change the port, use the `presto-config` configuration classification to set the `http-server.http.port` property. For more information, see [Config properties](https://prestodb.io/docs/current/installation/deployment.html#config-properties) in the *Deploying Presto* section of Presto Documentation.

## Issue with Hive Bucket execution in some releases
<a name="emr-presto-bucket-execution"></a>

Presto version 152.3 has an issue with Hive bucket execution that causes significantly slower Presto query performance in some circumstances. Amazon EMR versions 5.0.3, 5.1.0, and 5.2.0 include this version of Presto. To mitigate this issue, use the `presto-connector-hive` configuration classification to set the `hive.bucket-execution` property to `false`, as shown in the following example.

```
[
   {
      "Classification": "presto-connector-hive",
      "Properties": {
         "hive.bucket-execution": "false"
      }
   }
]
```