View Maintenance Policies

when to apply maintenance procedures on the materialized views

• Immediate View Maintenance
  Refreshing is done within the transaction that changes the base data. slow transactions; faster queries and always up to date results.
• Deferred View Maintenance
  • lazily, at query time
    fast transactions; slow query speed.
  • forced, after a certain amount of change to the base data
    non up to date results; good transaction and query time.
  • periodically, in certain time intervals
    non up to date results; good transaction and query time.

comparison of all in general; how the decision when to use which one is made.