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Oracle DBA - August 28, 2008 at 17:10 pm by Amit Satpute
How do you increase the performance of %LIKE operator?
The % placed after he search word can enable the use of index if one is
specified in the index column. This performs better than the other two ways of
using % - before the search word OR before and after the search word.
What is a standby database? Difference between Physical and logical standby
databases.
A standby database is a backup database that can be promoted should the primary
fail.
A physical standby database is created from an existing other database. This
other database will then be the primary database.
Logical Standby database makes the dml statements using archivelogs generated
and applies to the secondary database. Logical standby database permits you to
add additional objects like tables, indexes, etc to the database.
What is Cache Fusion Technology?
Cache fusion treats multiple buffer caches as one joint global cache.This solves
the issues like data consistency internally, without any impact on the
application code or design. Cache fusion technology eases the process of a very
high number of concurrent users and SQL operations without compromising data
consistency.
What is simple replication and advance replication?
Replication is the process of creating and maintaining replicas of database
objects in a distributed database system.
In simple replication, you create a snapshot, a table corresponding to the
query's column list. When the snapshot is refreshed, that underlying table is
populated with the results of the query. As data changes in a table in the
master database, the snapshot is refreshed as scheduled and moved to the
replicated database.
Advanced replication allows the simultaneous transfer of data between two or
more Master Sites. There are considerations to keep in mind when using
multi-master replication. The important ones are sequences (which cannot be
replicated), triggers (which can turn recursive if you're not careful) and
conflict resolution.
How are the indexes updated?
Whenever a table partition is modified using a DDL command, the associated index
partitions are placed in the default tablespace or in the same tablespace as
the data segments. This has been an issue with the previous releases of the
Oracle databases.
With the Oracle 10g release, it has become possible to modify the partitioned
table, using the UPDATE INDEXES clause. It can rebuild the associated index
segments automatically. It helps to reduce the level of management needed and
also enhances the availability of the data in the table.
You can create and Alter the table and update indexes to reflect the changes.
Latches vs Enqueues
Enqueues permit several concurrent processes to have varying degree of sharing
of resources. Any object which can be concurrently used, can be protected with
enqueues. The enqueue is obtained using an OS specific locking mechanism. An
enqueue allows the user to store a value in the lock.
In latches there is no ordered queue of waiters like in enqueues. Latch waiters
may use wakeup timers and retry or spin (only in multiprocessors). Since the
processes keep trying concurrently, any process can get the latch. The first
process to try might be the last one to get.
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