Apache Druid

Apache Druid is a high performance, real-time analytics database that delivers sub-second queries on streaming and batch data at scale and under load.

Prerequisite

Ensure that your Dremio cluster is at version 24.2 or later.

Configuring Apache Druid 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 Apache Druid.

General

1. In the Name field, specify the name by which you want the Druid source to appear in the list of data sources.
2. Under Connection, follow these steps:
   1. In the Host field, specify the hostname or IP address of the Druid source.
   2. In the Port field, specify the port to use. The default port is 8888.
   3. (Optional) Select Use SSL to use SSL to secure connections.
3. Under Authentication, specify the username and password for Dremio to use when connecting to the Druid source.

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.

Reflection Refresh

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

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 Druid Source

To edit a Druid source:

1. On the Datasets page, click Sources > Databases in the panel on the left. The list of data sources appears to the right.
2. Hover over the name of the Druid source.
3. Click to the right.
4. In the Source Settings dialog, you cannot edit the name. Editing other parameters is optional. For parameters and advanced options, see Configuring Apache Druid as a Source.
5. Click Save.

Removing a Druid Source

To remove a Druid source, perform these steps:

1. On the Datasets page, click Sources > Databases in the panel on the left. The list of data sources appears to the right.
2. Hover over the name of the Druid source.
3. Click to the right.
4. From the list of actions, click Remove Source. Confirm that you want to remove the source.

note

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

Predicate Pushdowns

These operations are performed by Druid:

!=
*
+
-
/
<
<=
<>
=
>
>=
abs
acos
and
asin
atan
atan2
avg
cast
ceil
concat
convert_timezone
cos
cot
degrees
floor
is not null
is null
length
like
ln
log
lower
lpad
ltrim
max
min
mod
not
or
power
radians
regexp_like
replace
reverse
round
rpad
rtrim
sign
sin
substr
substring
sum
tan
tanh
trim
upper
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