MongoDB Connector¶

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

Configuration¶

To configure the MongoDB connector, create a catalog properties file etc/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 etc/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:

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.ssl.enabled¶

This flag enables SSL connections to MongoDB servers.

This property is optional and defaults to false. If you set it to true and host Presto yourself, it’s likely that you also use a TLS CA file.

For setup instructions, see Configuring the MongoDB Connector to Use a TLS CA File.

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_SAFE, 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

1. Connect in replica set mode, and discover all members of the set based on the given servers

2. Make sure that the set name reported by all members matches the required set name.

3. 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.

This property is optional; the default is 0.

Configuring the MongoDB Connector to Use a TLS CA File¶

A TLS CA file may be required to connect securely to a MongoDB cluster hosted on DigitalOcean. MongoDB clusters are hosted on multiple nodes, each with its own hostname. Cluster hostnames do not resolve using standard dig requests to the hostname in the connection string.

Retrieve the Node Hostnames¶

To retrieve the node hostnames of a cluster using dig, specify the srv record type in the request and prepend _mongodb._tcp. to the hostname in the connection string, as shown below:

dig srv _mongodb._tcp.<cluster-hostname>

For example, a properly formatted dig request would look like this:

dig srv _mongodb._tcp.mongodb-prod-cluster-ba6e9b05.mongo.ondigitalocean.com

The dig command returns the actual hosts (in the Answer Section) that you can use to connect to MongoDB through Presto. The regular hostname won’t work and will result in a host not found error.

Set Up a TLS CA File¶

The following steps were developed using CentOS. Adapt them as needed for your environment.

1. Create the certificate file:

   touch /etc/pki/ca-trust/source/anchors/mongo.prod-cluster.crt
   

2. Paste the contents of the TLS CA file into the newly created file.

3. Update the trust store by running the following command:

   update-ca-trust
   

4. Verify the setup by running the following command:

   openssl s_client -connect <host-found-with-dig-above>:27017 < /dev/null
   

   The output should include CONNECTED and Verification: OK, indicating the SSL connection is properly configured.

Configure the Catalog¶

To configure a MongoDB catalog for this cluster, follow these steps:

1. Create the catalog configuration file:

   touch etc/catalog/mongodb.properties
   

2. Edit the file and include the host found using dig in Retrieve the Node Hostnames. For example:

   connector.name=mongodb
   mongodb.seeds=<host-found-with-dig-above>:27017
   mongodb.credentials=<user>:<password>@<mongodb-auth-source>
   mongodb.ssl.enabled=true
   mongodb.required-replica-set=<mongodb-replica-set>
   

Run Queries¶

After starting the Presto server, you should be able to connect to the catalog and execute queries. For instance:

SELECT name
FROM users
WHERE _id = ObjectId('66fe8898c4ce1100c811cbe0');

Table Definition¶

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

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

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

Each field definition:

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

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)

SQL support¶

ALTER TABLE¶

ALTER TABLE mongodb.admin.sample_table ADD COLUMN new_col INT;
ALTER TABLE mongodb.admin.sample_table DROP COLUMN new_col;
ALTER TABLE mongodb.admin.sample_table RENAME COLUMN is_active TO is_enabled;
ALTER TABLE mongodb.admin.sample_table RENAME TO renamed_table;

ALTER TABLE mongodb.admin.users ALTER COLUMN age TYPE BIGINT;