Basic Replication in Oracle - (Read – only Materialized Views)

A. Read – only Materialized Views

I. Overview

• Clients can query data at the local machine without having to remote machines Master Database. Helps reduce query time and reduce the load for the Master Database server.
• Clients only read the data on the local machine (Read - only Materialized Views) can not update, delete, ...
• Only can update, delete, ... data on the master machine with the user account has the ability (eg, SYS, SYSTEM, or the user is granted the right ...).
• Each table in the computer while updating the Master Database after 1 period (Do configuration), data change will automatically update to the machine Slave (Read - only Materialized Views

• 1 read - only table snapshot: 1 copy table data from one or more other tables on the remote machine (master machine.), Along with the update logs.
• Ex: From a table on master:

SQL> CREATE SNAPSHOT obj_1 AS  SELECT * FROM obj_1@orc1

SQL> CREATE SNAPSHOT sales.orders AS   SELECT * FROM sales.orders@hq.acme.com o
WHERE EXISTS
  ( SELECT c_id FROM sales.customers@hq.acme.com c
WHERE o.c_id = c.c_id AND zip = 19555);

• Snapshot logs: For each replicated table (taken back to the slave) to create one snapshot log (Made by the owner of the table). Snapshot logs table name:

table user_snapshot_log
MLOG$_name_of_table_replicated

• Snapshot Refreshes : Refresh snapshot than master.
• Snapshot Refreshes Groups : Refresh groups in the Groups table snapshot.
• Automatic Snapshot Refreshes: Automatically refresh. When you create a snapshot refresh group, the administrator should configure automatic refresh. However, it can refresh manually when necessary.

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