There are a couple of items that may be worth noting about the implementation. In Roxie, before executing the query, all library graphs are expanded into the query graph. Any datasets that are supplied as parameters to the library (or a dataset inside an interface parameter) are directly connected to the place they are used in the query library, and only results that are used are evaluated. This means that using a query library should have very little overhead compared with including the ECL code directly in the query. NOTE: Datasets inside row parameters aren't streamed, so passing a ROW containing a dataset as a parameter to the library is not as efficient as using an INTERFACE.

The implementation in hthor is not as efficient. Dataset parameters are fully evaluated, and passed to the library as a complete unit block and all results are evaluated. Thor does not yet support query libraries.

The other item of note is that if libraryA uses libraryC, and libraryB also uses libraryC with the same parameters, the calls from different libraries will not be commoned up. However if an attribute exported from an instance of libraryC is passed to libraryA and libraryB, then the calls to libraryC will be commoned up. The way attributes currently tend to be structured in the repository, e.g., calculating get_Dids() and passing that into other attributes means this is unlikely to cause any issues in practice.