MongoDB connector

The mongodb connector allows the use of MongoDB collections as tables in Trino.

Requirements

To connect to MongoDB, you need:

• MongoDB 4.2 or higher.
• Network access from the Trino coordinator and workers to MongoDB. Port 27017 is the default port.
• Write access to the schema information collection in MongoDB.

Configuration

To configure the MongoDB connector, create a catalog properties file etc/catalog/example.properties with the following contents, replacing the properties as appropriate:

connector.name=mongodb
mongodb.connection-url=mongodb://user:pass@sample.host:27017/

Multiple MongoDB clusters

You can have as many catalogs as you need, so if you have additional MongoDB clusters, simply add another properties file to etc/catalog with a different name, making sure it ends in .properties). For example, if you name the property file sales.properties, Trino will create a catalog named sales using the configured connector.

Configuration properties

The following configuration properties are available:

Property name	Description
mongodb.connection-url	The connection url that the driver uses to connect to a MongoDB deployment
mongodb.schema-collection	A collection which contains schema information
mongodb.case-insensitive-name-matching	Match database and collection names case insensitively
mongodb.min-connections-per-host	The minimum size of the connection pool per host
mongodb.connections-per-host	The maximum size of the connection pool per host
mongodb.max-wait-time	The maximum wait time
mongodb.max-connection-idle-time	The maximum idle time of a pooled connection
mongodb.connection-timeout	The socket connect timeout
mongodb.socket-timeout	The socket timeout
mongodb.tls.enabled	Use TLS/SSL for connections to mongod/mongos
mongodb.tls.keystore-path	Path to the or JKS key store
mongodb.tls.truststore-path	Path to the or JKS trust store
mongodb.tls.keystore-password	Password for the key store
mongodb.tls.truststore-password	Password for the trust store
mongodb.read-preference	The read preference
mongodb.write-concern	The write concern
mongodb.required-replica-set	The required replica set name
mongodb.cursor-batch-size	The number of elements to return in a batch
mongodb.allow-local-scheduling	Assign MongoDB splits to a specific worker
mongodb.dynamic-filtering.wait-timeout	Duration to wait for completion of dynamic filters during split generation

mongodb.connection-url

A connection string containing the protocol, credential, and host info for use in connecting to your MongoDB deployment.

For example, the connection string may use the format mongodb://<user>:<pass>@<host>:<port>/?<options> or mongodb+srv://<user>:<pass>@<host>/?<options>, depending on the protocol used. The user/pass credentials must be for a user with write access to the schema information collection.

See the MongoDB Connection URI for more information.

This property is required; there is no default. A connection URL must be provided to connect to a MongoDB deployment.

mongodb.schema-collection

As MongoDB is a document database, there is no fixed schema information in the system. So a special collection in each MongoDB database should define the schema of all tables. Please refer the MongoDB connector section for the details.

At startup, the connector tries to guess the data type of fields based on the type mapping.

The initial guess can be incorrect for your specific collection. In that case, you need to modify it manually. Please refer the MongoDB connector section for the details.

Creating new tables using CREATE TABLE and CREATE TABLE AS SELECT automatically create an entry for you.

This property is optional; the default is _schema.

mongodb.case-insensitive-name-matching

Match database and collection names case insensitively.

This property is optional; the default is false.

mongodb.min-connections-per-host

The minimum number of connections per host for this MongoClient instance. Those connections are kept in a pool when idle, and the pool ensures over time that it contains at least this minimum number.

This property is optional; the default is 0.

mongodb.connections-per-host

The maximum number of connections allowed per host for this MongoClient instance. Those connections are kept in a pool when idle. Once the pool is exhausted, any operation requiring a connection blocks waiting for an available connection.

This property is optional; the default is 100.

mongodb.max-wait-time

The maximum wait time in milliseconds, that a thread may wait for a connection to become available. A value of 0 means that it does not wait. A negative value means to wait indefinitely for a connection to become available.

This property is optional; the default is 120000.

mongodb.max-connection-idle-time

The maximum idle time of a pooled connection in milliseconds. A value of 0 indicates no limit to the idle time. A pooled connection that has exceeded its idle time will be closed and replaced when necessary by a new connection.

This property is optional; the default is 0.

mongodb.connection-timeout

The connection timeout in milliseconds. A value of 0 means no timeout. It is used solely when establishing a new connection.

This property is optional; the default is 10000.

mongodb.socket-timeout

The socket timeout in milliseconds. It is used for I/O socket read and write operations.

This property is optional; the default is 0 and means no timeout.

mongodb.tls.enabled

This flag enables TLS connections to MongoDB servers.

This property is optional; the default is false.

mongodb.tls.keystore-path

The path to the PEM or JKS key store.

This property is optional.

mongodb.tls.truststore-path

The path to PEM or JKS trust store.

This property is optional.

mongodb.tls.keystore-password

The key password for the key store specified by mongodb.tls.keystore-path.

This property is optional.

mongodb.tls.truststore-password

The key password for the trust store specified by mongodb.tls.truststore-path.

This property is optional.

mongodb.read-preference

The read preference to use for queries, map-reduce, aggregation, and count. The available values are PRIMARY, PRIMARY_PREFERRED, SECONDARY, SECONDARY_PREFERRED and NEAREST.

This property is optional; the default is PRIMARY.

mongodb.write-concern

The write concern to use. The available values are ACKNOWLEDGED, JOURNALED, MAJORITY and UNACKNOWLEDGED.

This property is optional; the default is ACKNOWLEDGED.

mongodb.required-replica-set

The required replica set name. With this option set, the MongoClient instance performs the following actions:

#. Connect in replica set mode, and discover all members of the set based on the given servers
#. Make sure that the set name reported by all members matches the required set name.
#. Refuse to service any requests, if authenticated user is not part of a replica set with the required name.

This property is optional; no default value.

mongodb.cursor-batch-size

Limits the number of elements returned in one batch. A cursor typically fetches a batch of result objects and stores them locally. If batchSize is 0, Driver's default are used. If batchSize is positive, it represents the size of each batch of objects retrieved. It can be adjusted to optimize performance and limit data transfer. If batchSize is negative, it limits the number of objects returned, that fit within the max batch size limit (usually 4MB), and the cursor is closed. For example if batchSize is -10, then the server returns a maximum of 10 documents, and as many as can fit in 4MB, then closes the cursor.

note

Do not use a batch size of 1.

This property is optional; the default is 0.

mongodb.allow-local-scheduling

Set the value of this property to true if Trino and MongoDB share the same cluster, and specific MongoDB splits should be processed on the same worker and MongoDB node. Note that a shared deployment is not recommended, and enabling this property can lead to resource contention.

This property is optional, and defaults to false.

mongodb.dynamic-filtering.wait-timeout

Duration to wait for completion of dynamic filters during split generation.

This property is optional; the default is 5s.

Table definition

MongoDB maintains table definitions on the special collection where mongodb.schema-collection configuration value specifies.

note

The plugin cannot detect that a collection has been deleted. You must delete the entry by executing db.getCollection("_schema").remove( { table: deleted_table_name }) in the MongoDB Shell. You can also drop a collection in Trino by running DROP TABLE table_name.

A schema collection consists of a MongoDB document for a table.

{
    "table": ...,
    "fields": [
          { "name" : ...,
            "type" : "varchar|bigint|boolean|double|date|array(bigint)|...",
            "hidden" : false },
            ...
        ]
    }
}

The connector quotes the fields for a row type when auto-generating the schema; however, the auto-generated schema must be corrected manually in the collection to match the information in the tables.

Manually altered fields must be explicitly quoted, for example, row("UpperCase" varchar).

Field	Required	Type	Description
table	required	string	Trino table name
fields	required	array	A list of field definitions. Each field definition creates a new column in the Trino table.

Each field definition:

{
    "name": ...,
    "type": ...,
    "hidden": ...
}

Field	Required	Type	Description
name	required	string	Name of the column in the Trino table.
type	required	string	Trino type of the column.
hidden	optional	boolean	Hides the column from DESCRIBE <table name> and SELECT *. Defaults to false.

There is no limit on field descriptions for either key or message.

ObjectId

MongoDB collection has the special field _id. The connector tries to follow the same rules for this special field, so there will be hidden field _id.

CREATE TABLE IF NOT EXISTS orders (
    orderkey BIGINT,
    orderstatus VARCHAR,
    totalprice DOUBLE,
    orderdate DATE
);

INSERT INTO orders VALUES(1, 'bad', 50.0, current_date);
INSERT INTO orders VALUES(2, 'good', 100.0, current_date);
SELECT _id, * FROM orders;

                 _id                 | orderkey | orderstatus | totalprice | orderdate
-------------------------------------+----------+-------------+------------+------------
 55 b1 51 63 38 64 d6 43 8c 61 a9 ce |        1 | bad         |       50.0 | 2015-07-23
 55 b1 51 67 38 64 d6 43 8c 61 a9 cf |        2 | good        |      100.0 | 2015-07-23
(2 rows)

SELECT _id, * FROM orders WHERE _id = ObjectId('55b151633864d6438c61a9ce');

                 _id                 | orderkey | orderstatus | totalprice | orderdate
-------------------------------------+----------+-------------+------------+------------
 55 b1 51 63 38 64 d6 43 8c 61 a9 ce |        1 | bad         |       50.0 | 2015-07-23
(1 row)

You can render the _id field to readable values with a cast to VARCHAR:

SELECT CAST(_id AS VARCHAR), * FROM orders WHERE _id = ObjectId('55b151633864d6438c61a9ce');

           _id             | orderkey | orderstatus | totalprice | orderdate
---------------------------+----------+-------------+------------+------------
 55b151633864d6438c61a9ce  |        1 | bad         |       50.0 | 2015-07-23
(1 row)

ObjectId timestamp functions

The first four bytes of each ObjectId represent an embedded timestamp of its creation time. Trino provides a couple of functions to take advantage of this MongoDB feature.

objectid_timestamp(ObjectId) -> timestamp

Extracts the TIMESTAMP WITH TIME ZONE from a given ObjectId:

SELECT objectid_timestamp(ObjectId('507f191e810c19729de860ea'));
-- 2012-10-17 20:46:22.000 UTC

timestamp_objectid(timestamp) -> ObjectId

Creates an ObjectId from a TIMESTAMP WITH TIME ZONE:

SELECT timestamp_objectid(TIMESTAMP '2021-08-07 17:51:36 +00:00');
-- 61 0e c8 28 00 00 00 00 00 00 00 00

In MongoDB, you can filter all the documents created after 2021-08-07 17:51:36 with a query like this:

db.collection.find({"_id": {"$gt": ObjectId("610ec8280000000000000000")}})

In Trino, the same can be achieved with this query:

SELECT *
FROM collection
WHERE _id > timestamp_objectid(TIMESTAMP '2021-08-07 17:51:36 +00:00');

Fault-tolerant execution support

The connector supports Fault-tolerant execution of query processing. Read and write operations are both supported with any retry policy.

Type mapping

Because Trino and MongoDB each support types that the other does not, this connector modifies some types when reading or writing data. Data types may not map the same way in both directions between Trino and the data source. Refer to the following sections for type mapping in each direction.

MongoDB to Trino type mapping

The connector maps MongoDB types to the corresponding Trino types following this table:

MongoDB to Trino type mapping

MongoDB type	Trino type	Notes
Boolean	BOOLEAN
Int32	BIGINT
Int64	BIGINT
Double	DOUBLE
Decimal128	DECIMAL(p, s)
Date	TIMESTAMP(3)
String	VARCHAR
Binary	VARBINARY
ObjectId	ObjectId
Object	ROW
Array	ARRAY	Map to ROW if the element type is not unique.
DBRef	ROW

No other types are supported.

Trino to MongoDB type mapping

The connector maps Trino types to the corresponding MongoDB types following this table:

Trino to MongoDB type mapping

Trino type	MongoDB type
BOOLEAN	Boolean
BIGINT	Int64
DOUBLE	Double
DECIMAL(p, s)	Decimal128
TIMESTAMP(3)	Date
VARCHAR	String
VARBINARY	Binary
ObjectId	ObjectId
ROW	Object
ARRAY	Array

No other types are supported.

SQL support

The connector provides read and write access to data and metadata in MongoDB. In addition to the globally available and read operation statements, the connector supports the following features:

• INSERT
• DELETE
• CREATE TABLE
• CREATE TABLE AS
• DROP TABLE
• ALTER TABLE
• CREATE SCHEMA
• DROP SCHEMA
• COMMENT

ALTER TABLE

The connector supports ALTER TABLE RENAME TO, ALTER TABLE ADD COLUMN and ALTER TABLE DROP COLUMN operations. Other uses of ALTER TABLE are not supported.

Table functions

The connector provides specific table functions to access MongoDB.

query(database, collection, filter) -> table

The query function allows you to query the underlying MongoDB directly. It requires syntax native to MongoDB, because the full query is pushed down and processed by MongoDB. 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.

For example, get all rows where regionkey field is 0:

SELECT
  *
FROM
  TABLE(
    example.system.query(
      database => 'tpch',
      collection => 'region',
      filter => '{ regionkey: 0 }'
    )
  );