1. A computer-implemented method comprising: a. In a target system, accessing a plurality of record identifiers received from an external source database; b. Storing the plurality of record identifiers in an electronic memory (“memory”) of the target system as elements of a software stack (“stack”); c. Reading a first plurality of the plurality of record identifiers (“first plurality”) from the stack and into a first thread, whereby the first plurality is thereupon excluded from the stack; d. Applying the first thread to retrieve from the source database each record associated with each record identifier of the first plurality; and e. Asynchronous writing of newly accessed additional record identifiers contemporaneously with sequentially writing of record identifiers from the stack into a plurality of threads, wherein each thread of the plurality of threads applies each received record identifier to retrieve from the source database each record associated with each received record identifier.