When Parallel Processing Occurs

Parallel plans can occur on both a single coserver and across multiple coservers:

• On a single coserver
  • The tables accessed by the query are fragmented across separate dbspaces on separate disks on the coserver.
  • An SQL operator in the query plan processes so much data that it requires multiple threads to execute in parallel, using CPU virtual processors on the single coserver.
• On multiple coservers

  Higher levels of parallelism occur when the accessed tables are fragmented across more than one coserver and multiple CPU virtual processors on the coservers execute the SQL operators in parallel.