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    Connecting to Another Dremio Software Cluster

    You can add a Dremio Software cluster as a data source. Such a cluster is referred to as a data-source cluster. The Dremio cluster that you add it to is referred to as a querying cluster.

    A data-source cluster gives a querying cluster access to one or more data sources, such as Amazon S3, Hive, and Postgres, that are connected to the data-source cluster. Dremio treats the connected Dremio cluster as any other supported data source. The data sources that are connected to the data-source cluster are represented as schemas. From a querying cluster, you can drill down into the schemas to see source datasets. You can then promote source datasets to tables, create reflections and views on those tables, and views on the views, and so on.

    Example

    In this diagram, there are two Dremio Software clusters: Dremio_1 and Dremio_2. Suppose that you wanted to access DataSource_2 from Dremio_1. To do so, you would add Dremio_2 as a data source to Dremio_1. In fact, you could add any number of Dremio Software clusters as data sources.

    Connecting one Dremio Software cluster to another

    In the UI for Dremio_1, Dremio_2 is listed under Sources > Databases. If you were to select Dremio_2 there, you would see the folder DataSource_2. Double-clicking that folder would show a list of the folders or schemas in that data source.

    An administrator can promote a table on a data source connected through a data-source cluster, just as it is possible to do on data source that is directly connected to a querying cluster. For example, an administrator promotes table DataSource_1.Table_1 from DataSource_1.Source_1 on the data source directly connected to Dremio_1, and also promotes table Dremio_2.DataSource_2.Table_2 from DataSource_2.Source_2 via the data-source cluster.

    Connecting to a data source directly and through a Dremio Software cluster

    The administrator can then use the tables as any other table, by querying them, creating views on them, and creating reflections on them.

    If Dremio_1 were connected to two Dremio clusters, the administrator could promote tables on both. Then, business users could run queries and view reports that federated data across the two data-source clusters.

    Queries can federate data that is in two or more clusters.

    And while business users run queries through the querying-cluster, other business users can continue running queries directly through a data-source cluster. Business users can still query data-source clusters directly.

    warning:

    • Ensure that the Dremio instance that you connect to does not itself connect to your original Dremio instance. For example, if Dremio_1 connects to Dremio_2 as a data source, ensure that Dremio_2 does not connect to Dremio_1 as a data source. Avoid recursive loops.

    • Querying across more than one region or more than one cloud vendor might increase query latency. Querying across cloud vendors also might result in egress charges from cloud vendors. For example, in this diagram DataSource_1 is using one cloud vendor, while DataSource_2 is using a different cloud vendor. Queries from Dremio_1 across Dremio_2 and Dremio_3 against those two data sources might incur egress charges from the cloud vendors. Federating data across cloud vendors can incur egress charges.

    note:

    Recommendation: Configure full TLS wire encryption on querying clusters and data-source clusters. See Full Wire Encryption

    User Impersonation

    When you connect a querying cluster to a data-source cluster, you provide the username and password of an account on the data-source cluster. By default, queries that run from the querying cluster against the data-source cluster run under the username of that account.

    You can instead allow users running queries from the querying cluster to run them under their own usernames on the data-source cluster. For example, User 1 on the querying cluster Dremio 1 can run queries as User 1 on the data-source cluster. User 1 must have an account on the data-source cluster, and that account must use the same username. User impersonation (also known as inbound impersonation) must be set up on the data-source cluster. See Inbound Impersonation.

    Limitation

    You cannot query columns that use complex data types, such as LIST, STRUCT, and MAP. Columns of complex data types do not appear in result sets.

    Prerequisites

    • You must have a username and password for the account on a data-source cluster to use for connections from the querying cluster.
    • The querying cluster and data-source clusters must all be at version 23.1 or later.

    Configuring Another Dremio Software Cluster as a Source

    1. In the bottom-left corner of the Datasets page, click Add Source.
    2. Under Databases in the Add Data Source dialog, select Dremio.

    General Options

    1. In the Name field, specify the name by which you want the data-source cluster to appear in the Databases section.
    2. Under Connection, specify how you want to connect to the data-source cluster.
      • Direct: Connect directly to a coordinator node of the cluster.
      • ZooKeeper: Connect to an external ZooKeeper instance that is coordinating the nodes of the cluster.
    3. In the Host and Port field, specify the hostname or IP address, and the port number, of the coordinator node or ZooKeeper instance.
    4. If the data-source cluster is configured to use TLS for connections to it, select the Use SSL option.
    5. Under Authentication, specify the username and password for the querying cluster to use when connecting to the data-source cluster.

    Advanced Options

    On the Advanced Options page, you can set values for these non-required options:

    Option Description
    Maximum Idle Connections The total number of connections allowed to be idle at a given time. The default maximum idle connections is 8.
    Connection Idle Time The amount of time (in seconds) allowed for a connection to remain idle before the connection is terminated. The default connection idle time is 60 seconds.
    Query Timeout The amount of time (in seconds) allowed to wait for the results of a query. If this time expires, the connection being used is returned to an idle state.
    User Impersonation Allows users to run queries on the data-source cluster under their own user IDs, not the user ID for the account used to authenticate with the data-source cluster. Inbound impersonation must be configured on the data-source cluster. See Inbound Impersonation.

    Reflection Refresh Options

    On the Reflection Refresh page, set the policy that controls how often reflections are scheduled to be refreshed automatically, as well as the time limit after which reflections expire and are removed.

    Option Description
    Never refresh Select to prevent automatic reflection refresh, default is to automatically refresh.
    Refresh every How often to refresh reflections, specified in hours, days or weeks. This option is ignored if Never refresh is selected.
    Never expire Select to prevent reflections from expiring, default is to automatically expire after the time limit below.
    Expire after The time limit after which reflections expire and are removed from Dremio, specified in hours, days or weeks. This option is ignored if Never expire is selected.

    Metadata Options

    On the Metadata page, you can configure settings to refresh metadata and handle datasets.

    Dataset Handling

    These are the optional Dataset Handling parameters.

    Parameter Description
    Remove dataset definitions if underlying data is unavailable By default, Dremio removes dataset definitions if underlying data is unavailable. Useful when files are temporarily deleted and added back in the same location with new sets of files.

    Metadata Refresh

    These are the optional Metadata Refresh parameters:

    • Dataset Discovery: The refresh interval for fetching top-level source object names such as databases and tables. Set the time interval using this parameter.
    Parameter Description
    (Optional) Fetch every You can choose to set the frequency to fetch object names in minutes, hours, days, or weeks. The default frequency to fetch object names is 1 hour.
    • Dataset Details: The metadata that Dremio needs for query planning such as information required for fields, types, shards, statistics, and locality. These are the parameters to fetch the dataset information.
    Parameter Description
    Fetch mode You can choose to fetch only from queried datasets that are set by default. Dremio updates details for previously queried objects in a source. Fetching from all datasets is deprecated.
    Fetch every You can choose to set the frequency to fetch dataset details in minutes, hours, days, or weeks. The default frequency to fetch dataset details is 1 hour.
    Expire after You can choose to set the expiry time of dataset details in minutes, hours, days, or weeks. The default expiry time of dataset details is 3 hours.

    Privileges

    On the Privileges page, you can grant privileges to specific users or roles. See Access Controls for additional information about user privileges.

    1. (Optional) For Privileges, enter the user name or role name that you want to grant access to and click the Add to Privileges button. The added user or role is displayed in the Users table.
    2. (Optional) For the users or roles in the Users table, toggle the green checkmark for each privilege you want to grant on the Dremio source that is being created.
    3. Click Save after setting the configuration.

    Editing a Dremio Source

    To edit a Dremio source:

    1. In the Datasets UI, click External Sources at the bottom-left of the page. A list of sources is displayed.
    2. Under the Action column, click the Settings (gear) icon for the source you want to edit. From the list of actions, click Edit Details.

    Alternatively, you can click the source and click the Settings (gear) icon of the source.

    1. In the Edit Source dialog, you cannot edit the name. Editing other parameters is optional. For parameters and advanced options, see Configuring Another Dremio Software Cluster as a Source.
    2. Click Save.

    Removing a Dremio Source

    To remove a Dremio source, perform these steps:

    1. In the Datasets UI, click External Sources at the bottom-left of the page. A list of sources is displayed.
    2. Under the Action column, click the Settings (gear) icon for the source that you want to remove.
    3. From the list of actions, click Remove Source. Confirm that you want to remove the source.

    warning:

    Removing a source causes all downstream virtual datasets dependent on objects in this source to break.

    Predicate Pushdowns

    Querying clusters offload these operations to data-source clusters. Data-source cluster either process these operations or offload them to their connected data sources.

    &&, ||, !, AND, OR
    +, -, /, *, %
    <=, <, >, >=, =, <>, !=
    ABS
    ADD_MONTHS
    AVG
    BETWEEN
    CASE
    CAST
    CEIL
    CEILING
    CHARACTER_LENGTH
    CHAR_LENGTH
    COALESCE
    CONCAT
    CONTAINS
    COUNT
    COUNT_DISTINCT
    COUNT_DISTINCT_MULTI
    COUNT_FUNCTIONS
    COUNT_MULTI
    COUNT_STAR
    CURRENT_DATE
    CURRENT_TIMESTAMP
    DATE_ADD
    DATE_DIFF
    DATE_SUB
    DATE_TRUNC
    DATE_TRUNC_DAY
    DATE_TRUNC_HOUR
    DATE_TRUNC_MINUTE
    DATE_TRUNC_MONTH
    DATE_TRUNC_QUARTER
    DATE_TRUNC_WEEK
    DATE_TRUNC_YEAR
    DAYOFMONTH
    DAYOFWEEK
    DAYOFYEAR
    EXTRACT
    FLATTEN
    FLOOR
    ILIKE
    IN
    IS DISTINCT FROM
    IS NOT DISTINCT FROM
    IS NOT NULL
    IS NULL
    LAST_DAY
    LCASE
    LEFT
    LENGTH
    LIKE
    LOCATE
    LOWER
    LPAD
    LTRIM
    MAX
    MEDIAN
    MIN
    MOD
    NEXT_DAY
    NOT
    NVL
    PERCENTILE_CONT
    PERCENTILE_DISC
    PERCENT_RANK
    POSITION
    REGEXP_LIKE
    REPLACE
    REVERSE
    RIGHT
    ROUND
    RPAD
    RTRIM
    SIGN
    SQRT
    STDDEV
    STDDEV_POP
    STDDEV_SAMP
    SUBSTR
    SUBSTRING
    SUM
    TO_CHAR
    TO_DATE
    TRIM
    TRUNC
    TRUNCATE
    UCASE
    UPPER
    VAR_POP
    VAR_SAMP

    ZooKeeper