Indexing in Big Data
It looks like you can index your data according to thier SQL documentation for CREATE INDEX. Sample code from their docs:
CREATE INDEX [IF NOT EXISTS] index_name ON table_name ( column_name_to_be_indexed );
GridDB's specifications and rules on index creation:

For a table, an index with the same name as an existing index in the table cannot be created.


If a transaction under execution exists in a table subject to processing, the system will wait for these to be completed before creating the data.


An index cannot be created on a column of BLOB type and ARRAY type.


Up to 16 columns can be indexed.


Time series table does not allow a primary key in a composite index.

My recommendation would be to index on the fields you plan to most commonly use in predicates (JOIN, WHERE, and HAVING clauses) in your queries, as a starting point.