DQL

DQL is a distributed query language for DSA. DQL can act both as a DSLink and an embedded library into a DSLink.

DQL acts upon the connected broker by default.

Multi-Broker Queries

DQL shields the list query command from listing nodes on other brokers. This prevents massive queries that can cause a slowdown. This only applies to the list command.

To enable multi-broker list queries, add the following command at the front of your query:

option traverseBrokers=true |

QOS Subscriptions

DQL uses QOS 0 by default for value subscriptions. You can configure what QOS a query will use by adding the following command in any position in front of the subscribe command where 1 is any of 0 1 2 3:

option qos=1 |

Syntax

Query Examples

List all nodes in the network

list *

List all values

list * | filter $type

Subscribe to all values

list * | filter $type | subscribe

Subscribe to all strings

list * | filter $type="string" | subscribe

Subscribe to all numbers

list * | filter $type="number" | subscribe

Subscribe to all values that have the @mytag attribute

list * | filter @mytag | subscribe

Create a table all nodes to their names

list * | subscribe :name

Subscribe to all values in a DSLink, and create a table of the name and the value

list /downstream/System/* | filter $type | subscribe :name value

Subscribe to all values in a DSLink, where @unit is not equal to "%"

list /downstream/System/* | filter $type @unit!="%" | subscribe

Subscribe to all numbers in the network, and add a column that multiplies the value by 2

list * | filter $type="number" | subscribe | expression double="row.value * 2"

Subscribe to the 'of' (Open Files) child of each database in etsdb

list /downstream/etsdb/? | subscribe of

Build a table of all values in the network and what types they are

list * | filter $type | subscribe $type

Concatenate a string with each value in the network

list * | filter $type | subscribe | expression msg="'Value: ' + row.value"

Calculate the minimum of 50 and the number values in the network

list * | filter $type="number" | subscribe | expression min="Math.min(50, row.value)"

Subscribe to children on a single path

path /downstream/System | subscribe Memory_Usage

Publish multiple points to MongoDB

list /downstream/System | filter :metric | subscribe | invoke /downstream/MongoDB/local/SystemValues/publish(Path=%path, Value=%value)

List all brokers

list brokers

List nodes with multiple expressions

list /downstream, /upstream, /sys

List nodes under each broker

list brokers | sublist /downstream/?