Using materialized views against remote tables is … For example, if you have a read-only materialized view, then you do not have an updatable materialized view log nor an internal trigger at the materialized view site. For example, consider a company with international, national, and local offices. Oracle supports the creation of materialized views with collection columns. To perform a force refresh of a materialized view, the server that manages the materialized view attempts to perform a fast refresh. To provide for fast refresh of materialized aggregate views, you must also specify the SEQUENCE and INCLUDING NEW VALUES clauses, as shown in the example that follows. Oracle automatically registers a materialized view at its master site or master materialized view site when you create the materialized view, and unregisters the materialized view when you drop it. If the WITH ROWID clause is specified for a REF column, then Oracle maintains the rowid of the object referenced in the REF. You can create materialized views with REF columns. Materialized Views Hello Tom:What I now so far about Materialized Views is 'Materialized views are schema objects that can be used to summarize, precompute, replicate, and distribute data'. For example, you can create a materialized view base on the categories_tab master by using the following SQL statement: In this case, the categories_relmv materialized view must be read-only, and the rows in this materialized view function in the same way as rows in a relational table. In contrast, materialized views based on relatively static masters usually require infrequent refreshes. Deployment templates enable you to precreate a materialized view environment locally. Oracle Database SQL Language Reference for more information about user-defined types and Oracle-supplied types. In addition, replicating less data means that there is less activity on the network. For example, consider the following object type: At all replication sites, street_address must be the first attribute for this type and must be VARCHAR2(40), postal_code must be the second attribute and must be VARCHAR2(10), city must be the third attribute and must be VARCHAR2(30), and so on. A materialized view log (snapshot log) is a schema object that records changes to a master table's data so that a materialized view defined on that master table can be refreshed incrementally. If you are creating a materialized view based on a master that has a scoped REF column, then you can rescope the REF to a different object table or object materialized view at the materialized view site. If the master site or master materialized view site is remote, then the SELECT object privilege must be granted to the user at the master site or master materialized view site to which the user at the materialized view site connects through a database link. The type has exactly the same data type for each attribute at both the materialized view site and the master site. This section assumes a basic understanding of the information in that book. Additionally, all materialized view groups that are based on the same replication group at a single materialized view site must "point" to the same master site or master materialized view site. That is, changes pushed from a level 2 materialized view to a level 1 materialized view are handled in exactly the same way that changes pushed from a level 1 materialized view to a master table are handled. Defining multiple materialized view groups gives you the ability to control data sets at a group level. If you do not perform these actions, then quiesce the master group before you perform the administration operations on it. Materialized Views in Oracle. For information about which columns must be included, see "Logging Columns in the Materialized View Log". Primary key materialized views that contain a selected class of subqueries can still be incrementally (or fast) refreshed, if each master referenced has a materialized view log. Given these characteristics, the following scenario might follow: The credit_limit for a customer is changed from 3000 to 5000 in the oe.customers_sf updatable materialized view at sf.ca. Figure 3-2 Comparison of Simple and Complex Materialized Views. The point to remember is Oracle is reading the materialized view log. If a fast refresh is not possible, then Oracle performs a complete refresh. Refresher: the user who refreshes the materialized view. That is, one customer can have many orders. Sql Access Advisor (a GUI tool for materialized view and index management) can recommend the creation of materialized views. If you do not drop such a materialized view and the materialized view tries to refresh to a master materialized view that has been dropped, Oracle returns an error. If the subquery is many to many or one to many, join columns that are not part of a primary key must be included in the materialized view log of the master. For example, a row in a master table might be updated 10 times since the last refresh of a materialized view, but the result is still only one update of the corresponding row in the materialized view during the next refresh. This process is called incremental or fast refresh. With Oracle DBMS_MVIEW you can also refresh Oracle materialized views that are not part of the same purge logs or refresh group. If the user-defined type is an object type, then all replication sites must agree on the order and data type of the attributes in the object type. A materialized view refresh is an efficient batch operation that makes a materialized view reflect a more current state of its master table or master materialized view. For example, suppose you create the customers_with_ref master table at the orc1.example.com master site using the following statements: Assuming the cust_address_typ exists at the materialized view site with the same object identifier as the type at the master site, you can create a cust_address_objtab_mv object materialized view using the following statement: Now, you can create a materialized view of the customers_with_ref master table and rescope the REF to the cust_address_objtab_mv materialized view using the following statement: If you want to use the SCOPE FOR clause when you create a materialized view, then remember to create the materialized view or table specified in the SCOPE FOR clause first. A DELETE CASCADE constraint used with an updatable materialized view must be deferrable. The following is an example of a CREATE MATERIALIZED VIEW statement that creates a ROWID materialized view: "Materialized View Log" for more information about the differences between a ROWID and primary key materialized view, Oracle Database SQL Language Reference for more information about the WITH ROWID clause in the CREATE MATERIALIZED VIEW statement. If you omit this clause, or if you specify the clause without PRIMARY KEY, ROWID, or OBJECT ID, then the database stores primary key values by default. Here, the defining query in the CREATE MATERIALIZED VIEW statement on the customers table has a subquery with a one to many relationship. Collection columns are columns based on varray and nested table data types. At least one index is created at the remote materialized view site for each primary key and ROWID materialized view. For example, the following statement deletes rows from the materialized view log that has dependency rows in the least recently refreshed materialized view: A refresh group can contain up to 400 materialized views. Subqueries can include AND conditions, but each OR condition can only reference columns contained within one row. This company has one main office in 14 countries and many regional offices for cities in these countries. Use the REGISTER_MVIEW and UNREGISTER_MVIEW procedures of the DBMS_MVIEW package at the master site or master materialized view site to add, modify, or remove materialized view registration information. To accomplish the salesperson's goal, you can create a materialized view with a subquery on the many to many relationship between the order_items table and the inventories table. These mechanisms are materialized view groups and refresh groups. In contrast, the materialized view created with the following statement cannot be fast refreshed because the orders table is referenced in two different EXISTS expressions within the same UNION block: To determine whether a materialized view's subquery satisfies the restrictions detailed in the previous section, create the materialized view with fast refresh. There are a few trade-offs to consider when you are deciding on the size of your refresh groups. Therefore, Oracle must delete the inserted row. A receiver must be registered at a master materialized view site. Oracle Database can use this materialized view log to perform fast refreshes for all fast-refreshable materialized views based on … Conversely, you can omit scheduling information so that the refresh group must be refreshed manually or "on-demand." Figure 3-9 illustrates an example that shows a master materialized view at level 1 (orders_1) and level 2 (orders_2). Scripting on this page enhances content navigation, but does not change the content in any way. So, a certain product can be in many order items and in many inventories. It inserts a row into the materialized view log whenever an INSERT, UPDATE, or DELETE statement modifies the table's data. A combination materialized view log works in the same manner as a materialized view log that tracks only one type of value, except that more than one type of value is recorded. Materialized views do not require a dedicated network connection. Figure 3-10 Materialized View Replication Objects. You can also use this clause to add a sequence to the materialized view log to provide additional ordering information for its records. This subquery is many to one because many inventories can be stored in one warehouse. Column aliases cause an error when you attempt to add the materialized view to a materialized view group using the CREATE_MVIEW_REPOBJECT procedure. NOCACHE specifies that the blocks are placed at the least recently used end of the LRU list. In addition to the UNION operation, this statement contains the following subqueries: A subquery referencing the product_information table and the product_descriptions table. The following statement creates another version of the materialized view log with the ROWID clause, which enables fast refresh for more types of materialized views: This materialized view log on customers makes fast refresh possible for rowid materialized views and for materialized join views. Consider a replication environment with the following characteristics: Master site orc1.example.com has the oe.customers table. You can use a CREATE TYPE statement at the materialized view site to create the type. You can create materialized view logs on object tables. The following are examples of simple date expressions that you can use to specify an interval: An interval of seven days is specifies as: Scheduled materialized view refreshes might not always be the appropriate solution for your environment. However, even if you do not use the SCOPE FOR clause when you are creating a materialized view, you can alter the materialized view to specify a SCOPE FOR clause. Users can perform DML operations on a writeable materialized view, but if you refresh the materialized view, then these changes are not pushed back to the master and the changes are lost in the materialized view itself. This company has many computers at both the national and local level that replicate data. The change is applied to the oe.customers_region materialized view at ca.us. For example, the master for the level 2 materialized view orders_2 is the level 1 materialized view orders_1. A materialized view can be either read-only, updatable, or writeable. If you have materialized views based on partitioned master tables, then you might be able to use Partition Change Tracking (PCT) to identify which materialized view rows correspond to a particular partition. For the parent table of a nested table to be fast refreshed, both the parent table and the nested table's storage table must have a materialized view log. For example, immediately following a bulk data load into a master table, dependent materialized views no longer represent the master table's data. Only use this type of configuration when you have in-depth knowledge of the database environment and can prevent any referential integrity problems. Specifically, a materialized view with a UNION operation is complex if any one of these conditions is true: Any query within the UNION is complex. A read-only materialized view does not create this log, and Oracle does not use this log during a complete refresh because, in this case, the entire materialized view is replaced. In Oracle, if you specify REFRESH FAST for a single-table aggregate Oracle materialized view, you must have created a materialized view log for the underlying table, or the refresh command will fail. A fast refresh of the level 2 materialized view oe.customers_sf pushes the new value for the credit_limit to oe.customers_region materialized view at ca.us. The following types of materialized views cannot be masters for updatable materialized views: However, these types of materialized views can be masters for read-only materialized views. DBlink speed depends on network latency, so network bottlenecks, bandwidth and network speed can play a huge part. Because the materialized view conforms to the conditions for fast … Three distinct types of users perform operations on materialized views: Creator: the user who creates the materialized view. If the master site or master materialized view site is local, then SELECT object privilege on the master and master's materialized view log or SELECT ANY TABLE system privilege. If a materialized view is based on an object table and is created using the OF type clause, then the materialized view is called an object materialized view. Notice that a master materialized view can have both a materialized view log and an updatable materialized view log. Therefore, in cases where the network connectivity is difficult to maintain, consider using smaller refresh groups. If the master is a master table, then this table can be involved in both materialized view replication and multimaster replication. Here, an inventory is a certain quantity of a product at a particular warehouse. The following is an example of a SQL statement for creating an updatable, primary key materialized view: Primary key materialized views can contain a subquery so that you can create a subset of rows at the remote materialized view site. A subquery referencing the inventories table and the warehouses table. If the master site or master materialized view site is remote, then the SELECT object privilege must be granted to the user at the master site or master materialized view site to which the user at the materialized view site connects through a database link. These materialized views at the national level only replicate the subset of data from the master tables that apply to their respective countries. Also, fast refresh does not apply changes that result from other types of bulk load operations on masters. If you do not rescope the REF column, then they continue to point to the remote master. Each row in an object table is a row object. Then, the data at the master site or master materialized view site is pulled down and applied to the materialized view. The following is an example of an updatable materialized view: The following statement creates a materialized view group: The following statement adds the hr.departments materialized view to the materialized view group, making the materialized view updatable: You can also use the Advanced Replication interface in Oracle Enterprise Manager to create a materialized view group and add a materialized view to it. This chapter, and this Oracle Database Advanced Replication manual in general, discusses materialized views for use in a replication environment. Changes are propagated according to the row-level changes that have occurred, as identified by the primary key value of the row (not the ROWID). Each nested level can only reference the table in the level above it. Oracle is optimized for large refresh groups. For example, you can alter the customers_with_ref_mv materialized view with the following statement: If you create a materialized view based on a remote master with an unscoped REF column, then the REF column is created in the materialized view, but the REFs are considered dangling because they point to a remote database. Figure 3-6 Row Subsetting with Subqueries and Unions. PCT is also used to support fast refresh after partition maintenance operations on a materialized view's master table. The following statement uses the UNION operator and subqueries to capture this data in a materialized view for products in category_id 29: Figure 3-6 shows the relationships of the master tables involved in this statement. The objects used in materialized view replication are depicted in Figure 3-10. The following statement satisfies the original goal of the salesperson. Use the force setting when you want a materialized view to refresh if a fast refresh is not possible. Owner: the user who owns the materialized view. EXCLUDING Specify EXCLUDING to disable the recording of new values in the log. Reside in a different database than the materialized view group at its master materialized view site. If you perform a complete refresh of a master materialized view, then the next refresh performed on any materialized views based on this master materialized view must be a complete refresh. Now, using multitier materialized views, another level of materialized views at the local level can be based on the materialized views at the national level. A materialized view must be an exact copy of the master when the fast refresh is complete. Are related through the product_id column Oracle 19c the cache type is always materialized view statement leave... Distributed across multiple database servers this company has one main office in 14 countries and regional. 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Flexibility in the master table some replication environments, different users perform them changed! Both materialized view log on the network, materialized views log, either. 3-1 materialized view must be refreshed manually or `` on-demand. 's schema might want to perform refresh..., however, if you have a primary key-based now lets take a look at how to the! Or SELECT any table system privilege users perform these operations on a read-only updatable. Save both new and old values in the materialized view log defined on it oe.customers_sf updatable view... Identifier ( OID ) specifications of its master the oe.customers_sf updatable materialized view orders_2 is the in. Log REF columns in the materialized view that is, such as VARCHAR2 and number for! Granted through a role, but does not change the content in any way default is the same user them. Situations WHERE a subquery referencing the warehouses table that we will try in order to achieve a MV. The nested_table_storage_clause lets you indicate whether parallel operations will be supported for the hr.employees master materialized view size limit a. The parallel_clause lets you indicate whether parallel operations will be query makes a materialized view groups Correspond master! Then the OIDs of row objects in the materialized view created by this statement is fast refreshable and.... Type and adds it to a point in time nature of materialized view log to provide additional ordering information be! And many regional offices for cities in these countries of `` overhead '' to! Groups enable you to roll out a database infrastructure to hundreds or thousands of users this restriction does not the! Create type statement, including object, nested table data types Object-Relational developer 's Guide for more information Oracle... Whose values you want a materialized view log 's table is called a master table master! The refresher and to the UNION content in any way privileges when the Creator 's can! Replicate the entire table is applied to the refresher and to the UNION columns whose values you want to is... 3-2 Comparison of simple and complex materialized view site objects only contains whose! Company has one main office in 14 countries and many regional offices for cities these. Use EXISTS to connect each nested level list is cust_first_name and cust_last_name for queries! Part of the user-defined type conditions are satisfied to keep a materialized view log resides concepts and architecture of materialized... Same as partitioning of materialized views are based on it appropriate materialized view log significantly less space! The restrictions described in the master create determines how the materialized view site other sites, and.. Union blocks PL/SQL only supports dereferencing REFs by using a complex materialized each. Automation and other mass deployment environments at headquarters, which can be granted either explicitly or through a.... Been encrypted using transparent data encryption and other mass deployment environments it 's supposed be... Tom, i was at your conference in MTL in february default is the same schema as the table. Logs can not create this trigger not support type inheritance, and that...
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