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

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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 method
• Master Authentication method (default)
  • Username -- MongoDB user name
  • Password -- MongoDB password
• Authentication database -- Database to authenticate against.

Advanced Options

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• 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 -- Enable this option to treat field names as case insensitive. When enabled, Dremio will record all known variations of a field name when learning the schema and use all known variations when pushing an operation down to Mongo.
• Connection Properties -- A list of additional MongoDB connection parameters.

Reflection Refresh

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• 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

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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.