13.5. MongoDB Connector

This connector allows the use of MongoDB collections as tables in Presto.

Note

MongoDB 2.6+ is supported although it is highly recommend to use 3.0 or later.

Configuration

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

connector.name=mongodb
mongodb.seeds=host1,host:port

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 ~/.prestoadmin/catalog with a different name (making sure it ends in .properties). For example, if you name the property file sales.properties, Presto will create a catalog named sales using the configured connector.

Configuration Properties

The following configuration properties are available:

Property Name	Description
`mongodb.seeds`	List of all mongod servers
`mongodb.schema-collection`	A collection which contains schema information
`mongodb.credentials`	List of credentials
`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.connection-timeout`	The socket connect timeout
`mongodb.socket-timeout`	The socket timeout
`mongodb.socket-keep-alive`	Whether keep-alive is enabled on each socket
`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.seeds`

Comma-separated list of hostname[:port] all mongod servers in the same replica set or a list of mongos servers in the same sharded cluster. If port is not specified, port 27017 will be used.

This property is required; there is no default and at least one seed must be defined.

`mongodb.schema-collection`

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

At startup, this connector tries guessing fields’ types, but it might not be correct for your collection. In that case, you need to modify it manually. CREATE TABLE and CREATE TABLE AS SELECT will create an entry for you.

This property is optional; the default is _schema.

`mongodb.credentials`

A comma separated list of username:password@collection credentials

This property is optional; no default value.

`mongodb.min-connections-per-host`

The minimum number of connections per host for this MongoClient instance. Those connections will be kept in a pool when idle, and the pool will ensure 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 will be kept in a pool when idle. Once the pool is exhausted, any operation requiring a connection will block 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 will not wait. A negative value means to wait indefinitely for a connection to become available.

This property is optional; the default is 120000.

`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.socket-keep-alive`

This flag controls the socket keep alive feature that keeps a connection alive through firewalls.

This property is optional; the default is false.

`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, FSYNC_SAFE, FSYNCED, JOURNAL_SAFEY, JOURNALED, MAJORITY, NORMAL, REPLICA_ACKNOWLEDGED, REPLICAS_SAFE 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 will

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 any member of the seed list 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 will be 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 will limit of number objects returned, that fit within the max batch size limit (usually 4MB), and cursor will be closed. For example if batchSize is -10, then the server will return a maximum of 10 documents and as many as can fit in 4MB, then close the cursor.

Note

Do not use a batch size of 1.

This property is optional; the default is 0.

Table Definition

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

Note

There’s no way for the plugin to detect a collection is deleted. You need to delete the entry by db.getCollection("_schema").remove( { table: deleted_table_name }) in the Mongo Shell. Or drop a collection by running DROP TABLE table_name using Presto.

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

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

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

Each field definition:

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

Field	Required	Type	Description
`name`	required	string	Name of the column in the Presto table.
`type`	required	string	Presto 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 orders3;

                 _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 orders3 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)

Note

Unfortunately, there is no way to represent _id fields more fancy like 55b151633864d6438c61a9ce.