Probabilistic indices for accessing authoring streams

In various implementations, streams are sent and received by a computing device engaged in an authoring session with respect to an electronic document. The computing device stores the streams in multiple container files associated with an instance of the electronic document open on the computing device. The device maintains an indices file to reflect a presence of the streams in the container files, such that fast access can be provided to the streams at a later time. The indices file comprises multiple probabilistic data structures corresponding to the container files that each indicate on a probabilistic basis whether a given stream is present in a corresponding one of the container files. The computing device uses the indices file to retrieve the streams from the container files.