Explain concurrency control?
Concurrency control
Oracles multiversion concurrency control varies from the concurrency mechanism used by some other data base vendors. Read only queries are given a read -consistent snapshot which is view if the data base as it existed at the particular point in time, having all update that we were committed by that point in time and not containing any updates that were not committed at any point in time therefore read clock are not used in read only queries don't interfere with other data base activity in term of locking.
Managed stand by data base
To make sure high availability oracle provide a managed stand by data base future A stand by data base is a copy of the regular data base i.e. in solved on the separate system. If a catastrophic failure occur on the primary system, the stand by system is activate and take over there by minimizing effect on failure on a availability. Oracle keeps the stand by data base up to date by constantly applying archived redo logs that are shipped from the primary data base the back up data base can be brought online in readonly mode and used for reporting and decision support queries