Unstructured data items are stored at an object storage service. A filtering criterion to be used to generate a result set for an access request is determined. A test that can be used to determine, without completing parsing of a record identified in an unstructured data item, whether the record satisfies the filtering criterion is identified. Parsing of a particular record is abandoned in response to determining, using the test, that the record satisfies the filtering criterion. A response to the access request is determined using a subset of records that satisfy the filtering criterion.