Lock-free creation of hash tables in parallel

A database system of lock-free creation of partitioned hash tables in parallel, comprising:

• a memory having computer readable instructions;
• and a processor for executing the computer readable instructions, the instructions comprising:
• partitioning a hash table of a database system;
• assigning a separate thread to each partition of the hash table;
• and
• executing a number of the separate threads in parallel with other threads without a lock, the executing comprising for each of said number:
• scanning an input data table and applying a hash function to each key in the input data table;
• and
• in response to the scanning:
• inserting data of keys that hash to the thread's partition into the thread's partition of the hash table;
• and
• ignoring keys that do not hash to the thread's partition,
• wherein an index is created for active buckets of the partition such that inactive buckets of the partition are no longer referenced and are automatically flushed to main memory, and
• wherein overflow data, in the partition, are stored in separate overflow buckets to be processed by another thread.

A computer program product for lock-free creation of partitioned hash tables in parallel for an input data table, the computer program product comprising a non-transitory computer readable storage medium having program code embodied therewith, the program code executable by a processor to:

• partition a hash table of a database system;
• assign a separate thread to each partition of the hash table;
• and
• execute a number of the separate threads in parallel with other threads without a lock, the executing comprising for each of said number:
• scanning the input data table and applying a hash function to each key in the input data table;
• and
• in response to the scanning:
• inserting data of keys that hash to the thread's partition into the thread's partition of the hash table;
• and
• ignoring keys that do not hash to the thread's partition,
• wherein an index is created for active buckets of the partition such that inactive buckets of the partition are no longer referenced and are automatically flushed to main memory, and
• wherein overflow data, in the partition, are stored in separate overflow buckets to be processed by another thread.