MongoDB

Supported Versions

Dremio supports MongoDB 3.6 through 6.1.

Limitation

DX-29932

Queries that un-nest nested fields are not allowed as they would cause incorrect schemas. This may be easily circumvented by pushing filters into the subquery or by simply not referencing the alias.

Dremio Configuration

General

 !

Connection

Name	Description
Hosts	A list of Mongo hosts. If MongoDB is sharded, enter the mongos hosts. Otherwise, enter the mongod host.
Port	A list of Mongo port numbers. Defaults to 27017.

• Connection Scheme -- Select how to connect to the source.
• Encrypt connection -- Forces an encrypted connection over SSL.
• Read from secondaries only -- Disables reading from primaries. Might degrade performance.

Authentication

• No Authentication

• Master Credentials (default):

  • Username: MongoDB user name

  • Password:

    • Dremio: Provide the MongoDB password in plain text. Dremio stores the password.

    • Azure Key Vault: Provide the URI for the Azure Key Vault secret that stores the MongoDB password. The URI format is https://<vault_name>.vault.azure.net/secrets/<secret_name> (for example, https://myvault.vault.azure.net/secrets/mysecret).

      note

      To use Azure Key Vault as your application secret store, you must:
      - Deploy Dremio on Azure.
      - Complete the Requirements for Authenticating with Azure Key Vault.

      It is not necessary to restart the Dremio coordinator when you rotate secrets stored in Azure Key Vault. Read Requirements for Secrets Rotation for more information.

    • AWS Secrets Manager: Provide the Amazon Resource Name (ARN) for the AWS Secrets Manager secret that holds the MongoDB password, which is available in the AWS web console or using command line tools.

    • HashiCorp Vault (Dremio 25.0.4+): Choose the HashiCorp secrets engine you're using from the dropdown menu and enter the secret reference for the MongoDB password in the correct format in the provided field.

  • Authentication database: Provide the name of the database that Dremio should authenticate against.

Advanced Options

 !

• Subpartition Size -- Number of records to be read by query fragments. This option can be used to increase query parallelism.
• Sample Size -- Number of records to be read when sampling to determine the schema for a collection. If zero the sample size is unlimited.
• Sample Method -- The method (First or Last) by which records should be read when sampling a collection to determine the schema.
• Auth Timeout (millis) -- Authentication timeout in milliseconds.
• Field names are case insensitive -- When enabled, Dremio reads all known variations of a field name when determining the schema, ignoring any value set for Sample Size. All field name variations are then used when pushing an operation down to Mongo.
• Connection Properties -- A list of additional MongoDB connection parameters.

Reflection Refresh

 !

• Never refresh -- Specifies how often to refresh based on hours, days, weeks, or never.
• Never expire -- Specifies how often to expire based on hours, days, weeks, or never.

Metadata

[](/images/mongo-metadata.png) !

Dataset Handling

• Remove dataset definitions if underlying data is unavailable (Default).
  If this box is not checked and the underlying files under a folder are removed or the folder/source is not accessible, Dremio does not remove the dataset definitions. This option is useful in cases when files are temporarily deleted and put back in place with new sets of files.

Metadata Refresh

• Dataset Discovery -- Refresh interval for top-level source object names such as names of DBs and tables.
  • Fetch every -- Specify fetch time based on minutes, hours, days, or weeks. Default: 1 hour
• Dataset Details -- The metadata that Dremio needs for query planning such as information needed for fields, types, shards, statistics, and locality.
  • Fetch mode -- Specify either Only Queried Datasets, All Datasets, or As Needed. Default: Only Queried Datasets
    • Only Queried Datasets -- Dremio updates details for previously queried objects in a source.
      This mode increases query performance because less work is needed at query time for these datasets.
    • All Datasets -- Dremio updates details for all datasets in a source. This mode increases query performance because less work is needed at query time.
    • As Needed -- Dremio updates details for a dataset at query time. This mode minimized metadata queries on a source when not used, but might lead to longer planning times.
  • Fetch every -- Specify fetch time based on minutes, hours, days, or weeks. Default: 1 hour
  • Expire after -- Specify expiration time based on minutes, hours, days, or weeks. Default: 3 hours

Sharing

 !

You can specify which users can edit. Options include:

• All users can edit.
• Specific users can edit.

Predicate Pushdowns

Dremio offloads these operations to MongoDB:

ABS
ADD
AND
CASE
CEIL
CONCAT
DAY_OF_MONTH
DIVIDE
EQUAL
EXP
FLOOR
GREATER
GREATER_OR_EQUAL
HOUR
LESS
LESS_OR_EQUAL
LN
LOG
LOG10
MAX
MIN
MINUTE
MOD
MONTH
MULTIPLY
NOT
NOT_EQUAL
OR
POW
REGEX
SECOND
SQRT
SUBSTR
SUBTRACT
TO_LOWER
TO_UPPER
TRUNC
YEAR

For More Information

• See MongoDB Data Types for information about mapping to Dremio data types.