getInputData(inputContext):Marks the beginning of the map/reduce script execution. Invokes the input stage. This function is invoked one time in the execution of the script.
map(mapContext): Optional, but if this entry point is skipped, the reduce(reduceContext) entry point is required. Invokes the map stage. If this entry point is used, the map function is invoked one time for each key/value pair provided by the getInputData(inputContext) function.
reduce: Optional, but if this entry point is skipped, the map(mapContext) entry point is required. Invokes the reduce stage. If this entry point is used, the reduce function is invoked one time for each key and list of values provided. Data is provided either by the map stage or, if the map stage is not used, by the getInputData stage.
summarize(summaryContext): Invokes the summarize stage. If the summarize entry point is used, the summarize function is invoked one time in the execution of the script.