DB2 uses parallel operations to access tables and indexes. This configuration impacts performance for queries that process large quantities of data across multiple table and index partitions. The response time for these data-or processor-intensive queries can be reduced.
The two types of query parallelism are as follows:
I/O parallelism manages concurrent I/O requests for a single query. I/O parallelism can fetch data using these multiple concurrent I/O requests into the buffers and significantly reduce the response time for large I/O bound queries.
Query CP parallelism breaks a large query into smaller queries and runs the smaller queries in parallel on multiple processors. This type of parallelism can also significantly reduce the elapsed time for large queries.
You can enable query parallelism by using the DEGREE ANY parameter of a BIND command or by setting the value of the CURRENT DEGREE special register to the value of ANY. Because there is overhead to the start of the parallel tasks, ensure that you use query parallelism for larger queries. For small queries, query parallelism can be a performance detriment.
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