Druid connector#

The Druid connector allows querying an Apache Druid database from Trino.

Requirements#

To connect to Druid, you need:

Druid version 0.18.0 or higher.
Network access from the Trino coordinator and workers to your Druid broker. Port 8082 is the default port.

Configuration#

Create a catalog properties file that specifies the Druid connector by setting the connector.name to druid and configuring the connection-url with the JDBC string to connect to Druid.

For example, to access a database as druid, create the file etc/catalog/druid.properties. Replace BROKER:8082 with the correct host and port of your Druid broker.

connector.name=druid
connection-url=jdbc:avatica:remote:url=http://BROKER:8082/druid/v2/sql/avatica/

You can add authentication details to connect to a Druid deployment that is secured by basic authentication by updating the URL and adding credentials:

connection-url=jdbc:avatica:remote:url=http://BROKER:port/druid/v2/sql/avatica/;authentication=BASIC
connection-user=root
connection-password=secret

Now you can access your Druid database in Trino with the druiddb catalog name from the properties file.

General configuration properties#

The following table describes general catalog configuration properties for the connector:

Property name	Description	Default value
`case-insensitive-name-matching`	Support case insensitive schema and table names.	`false`
`case-insensitive-name-matching.cache-ttl`		`1m`
`case-insensitive-name-matching.config-file`	Path to a name mapping configuration file in JSON format that allows Trino to disambiguate between schemas and tables with similar names in different cases.	`null`
`case-insensitive-name-matching.refresh-period`	Frequency with which Trino checks the name matching configuration file for changes.	`0` (refresh disabled)
`metadata.cache-ttl`	Duration for which metadata, including table and column statistics, is cached.	`0` (caching disabled)
`metadata.cache-missing`	Cache the fact that metadata, including table and column statistics, is not available	`false`
`metadata.cache-maximum-size`	Maximum number of objects stored in the metadata cache	`10000`
`write.batch-size`	Maximum number of statements in a batched execution. Do not change this setting from the default. Non-default values may negatively impact performance.	`1000`
`dynamic-filtering.enabled`	Push down dynamic filters into JDBC queries	`true`
`dynamic-filtering.wait-timeout`	Maximum duration for which Trino will wait for dynamic filters to be collected from the build side of joins before starting a JDBC query. Using a large timeout can potentially result in more detailed dynamic filters. However, it can also increase latency for some queries.	`20s`
`domain-compaction-threshold`	Minimum size of query predicates above which Trino compacts the predicates. Pushing down a large list of predicates to the data source can compromise performance. For optimization in that situation, Trino can compact the large predicates into a simpler range predicate. If necessary, adjust the threshold to ensure a balance between performance and predicate pushdown.	`32`

Procedures#

system.flush_metadata_cache()

Flush JDBC metadata caches. For example, the following system call flushes the metadata caches for all schemas in the example catalog
```
USE example.myschema;
CALL system.flush_metadata_cache();
```

Case insensitive matching#

When case-insensitive-name-matching is set to true, Trino is able to query non-lowercase schemas and tables by maintaining a mapping of the lowercase name to the actual name in the remote system. However, if two schemas and/or tables have names that differ only in case (such as “customers” and “Customers”) then Trino fails to query them due to ambiguity.

In these cases, use the case-insensitive-name-matching.config-file catalog configuration property to specify a configuration file that maps these remote schemas/tables to their respective Trino schemas/tables:

{
  "schemas": [
    {
      "remoteSchema": "CaseSensitiveName",
      "mapping": "case_insensitive_1"
    },
    {
      "remoteSchema": "cASEsENSITIVEnAME",
      "mapping": "case_insensitive_2"
    }],
  "tables": [
    {
      "remoteSchema": "CaseSensitiveName",
      "remoteTable": "tablex",
      "mapping": "table_1"
    },
    {
      "remoteSchema": "CaseSensitiveName",
      "remoteTable": "TABLEX",
      "mapping": "table_2"
    }]
}

Queries against one of the tables or schemes defined in the mapping attributes are run against the corresponding remote entity. For example, a query against tables in the case_insensitive_1 schema is forwarded to the CaseSensitiveName schema and a query against case_insensitive_2 is forwarded to the cASEsENSITIVEnAME schema.

At the table mapping level, a query on case_insensitive_1.table_1 as configured above is forwarded to CaseSensitiveName.tablex, and a query on case_insensitive_1.table_2 is forwarded to CaseSensitiveName.TABLEX.

By default, when a change is made to the mapping configuration file, Trino must be restarted to load the changes. Optionally, you can set the case-insensitive-name-mapping.refresh-period to have Trino refresh the properties without requiring a restart:

case-insensitive-name-mapping.refresh-period=30s

Type mapping#

Type mapping configuration properties#

The following properties can be used to configure how data types from the connected data source are mapped to Trino data types and how the metadata is cached in Trino.

Property name

Description

Default value

unsupported-type-handling

Configure how unsupported column data types are handled:

IGNORE, column is not accessible.
CONVERT_TO_VARCHAR, column is converted to unbounded VARCHAR.

The respective catalog session property is unsupported_type_handling.

IGNORE

jdbc-types-mapped-to-varchar

Allow forced mapping of comma separated lists of data types to convert to unbounded VARCHAR

SQL support#

The connector provides globally available and read operation statements to access data and metadata in the Druid database.

Table functions#

The connector provides specific table functions to access Druid.

`query(varchar) -> table`#

The query function allows you to query the underlying database directly. It requires syntax native to Druid, because the full query is pushed down and processed in Druid. This can be useful for accessing native features which are not available in Trino or for improving query performance in situations where running a query natively may be faster.

As an example, use STRING_TO_MV and MV_LENGTH from Druid SQL’s multi-value string functions to split and then count the number of comma-separated values in a column:

SELECT
  num_reports
FROM
  TABLE(
    druid.system.query(
      query => 'SELECT
        MV_LENGTH(
          STRING_TO_MV(direct_reports, ",")
        ) AS num_reports
      FROM company.managers'
    )
  );