Persistent edge queries

In previous chapters you learned how to run regular edge queries with Store-and-Forward (SNF). This chapter describes how to create persistent edge queries that run autonomously.

Persistent edge queries are defined using the OSQL type EdgeQuery. All instances of type EdgeQuery are always started when an edge listener is started.

The type EdgeQuery has the propeties:

create type EdgeQuery;
create function name(EdgeQuery eq) -> Charstring key as stored;
create function statement(EdgeQuery eq) -> Charstring as stored;
create function options(EdgeQuery eq) -> Record as stored;

As the function names name, statement, and options suggest, the properties of EdgeQuery are very similar to the arguments of edge_cq. The main difference is that the property name is essentially the id of the query when it runs autonomously on the edge.

When an edge starts it will go through all instances of EdgeQuery and start them. If you dynamically create more EdgeQuery objects during an interactive session they will be used at the next edge restart. You can activate a persistent edge query eq by calling run_stored_edge_query(eq).

Documentation of properties of the type Edgequery:

select doc(f)
  from Function f
 where f in methods(typenamed("Edgequery"))

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You can cancel a persistent edge query as usual with cancel_edge_cq(). However if you do not want the query to run again on the next restart of the edge you will have to update and save the local database to remove the instance of EdgeQuery.