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Oracle DBA Interview Questions

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Fast refresh maintains a change log table, which records change vectors, not unlike how the redo logs work. There is overhead to this, as with a table that has a LOT of indexes on it, and inserts and updates will be slower. However if you are performing refreshes often, like every few minutes, you want to do fast refresh so you don't have to full-table-scan the source table. Complete refresh is good if you're going to refresh once a day. Does a full table scan on the source table, and recreats the snapshot/mview. Also inserts/updates on the source table are NOT impacted on tables where complete refresh snapshots have been created.

It disables the logging of changes to the redologs. It does not disable ALL LOGGING, however as Oracle continues to use a base of changes, for recovery if you pull the plug on the box, for instance. However it will cause problems if you are using standby database. Use it to speed up operations, like an index rebuild, or partition maintenance operations.

Standby databases allow us to create a copy of our production db, for disaster recovery. We merely switch mode on the target db, and bring it up as read/write. Can setup as master->slave or master->master. The latter allows the former prod db to become the standby, once the failure cause is remedied. Watch out for NO LOGGING!! Be sure we're in archivelog mode.

RMAN is faster, can do incremental (changes only) backups, and does not place tablespaces into hotbackup mode.

With bind variables in SQL, Oracle can cache related queries a single time in the SQL cache (area). This avoids a hard parse each time, which saves on various locking and latching resources we use to check objects existence and so on. BONUS: For rarely run queries, especially BATCH queries, we explicitely DO NOT want to use bind variables, as they hide information from the Cost Based Opitmizer. For batch queries from 3rd party apps like peoplesoft, if we can't remove bind variables, we can use bind variable peeking!

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