Aggregating input into hashtables using just-in-time compilation of compilable code in response to a database query. Compilable code can be generated that is configured to cause a programmable processor to produce one or more hashmaps based on the input database. The one or more hashmaps can correspond to each individual thread from the input. The compilable code can be configured to cause the one or more processors to insert the hashmaps into a scheduler. Compilable code can be generated that is configured to: aggregate elements from the one or more hashmaps into buckets of elements having the same partition identity; rehash the buckets of elements having the same partition identity to reduce the number of groups within the bucket; facilitate the merger of all non-empty elements from each target-partition into a merged-partition.