Lock-free generation of columns with minimal dictionaries after parallel aggregation

A system comprising:

• computer hardware configured to perform operations comprising:
• generating a result column, the generating comprising a plurality of worker jobs running in parallel to read tasks from a shared queue as part of a query plan operation, the query plan operation comprising a group-by column within an input set of input columns, the group-by column comprising an original dictionary for all values contained within the group-by column;
• creating a new dictionary for the result column, the new dictionary preserving a same ordering as the original dictionary;
• determining that the new dictionary has fewer entries than the original dictionary for the group-by column such that mapping is required between old value identifiers within the group-by column and new value identifiers within the result column;
• and
• renaming the old value identifiers to the new value identifiers using a mapping vector.

A computer-implemented method comprising:

• generating a result column, the generating comprising a plurality of worker jobs running in parallel to read tasks from a shared queue as part of a query plan operation, the query plan operation comprising a group-by column within an input set of input columns, the group-by column comprising an original dictionary for all values contained within the group-by column;
• creating a new dictionary for the result column, the new dictionary preserving a same ordering as the original dictionary;
• determining that the new dictionary has fewer entries than the original dictionary for the group-by column such that mapping is required between old value identifiers within the group-by column and new value identifiers within the result column;
• and
• renaming the old value identifiers to the new value identifiers using a mapping vector.