MapReduce jobs to score measured spectra. Spectra are scored against the contents of the peptide database with a series of m/z values. In the next job all scores are combined to generate the best scores. As a single file is the desired output, the last job has a single reducer allowing all output to go to a single file.
Lewis et al. BMC Bioinformatics 2012 13:324 doi:10.1186/1471-2105-13-324