materialized view log in oracle 11g with example

Specifying Join Columns for Materialized View Logs: Example The following statement creates a materialized view log on the order_items table of the sample oe schema. For example, if you need to support multiple users within the same database at a materialized view site, then you might want to create multiple materialized view groups for a target master group. In this case, the storage table is phone_store_ntab and the parent table is people_reltab. When you create the inventories materialized view, you want to retrieve the inventories with the quantity on hand greater than zero for the products that appear in the order_items table. 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. The problem is when we need to refresh our Materialized Views, a … This requirement includes LOB columns with NOT NULL constraints. Special care on view log. Issue the CREATE TYPE statement and specify the OID: The type is now ready for use at the materialized view site. If the collection column is a nested table, then you can optionally specify the nested_table_storage_clause during materialized view creation. For information about which columns must be included, see "Logging Columns in the Materialized View Log". When a fast refresh is performed on a materialized view, Oracle must examine all of the changes to the master table or master materialized view since the last refresh to see if any apply to the materialized view. In addition to the materialized view mechanisms described in the previous section, several other mechanisms organize the materialized views at the materialized view site. If you do not use the replication management API for these actions, then replication errors might result. INCLUDING Specify INCLUDING to save both new and old values in the log. As described in the previous section, the internal trigger adds change information to the materialized view log whenever a DML transaction has taken place on the target master. A materialized view that is acting as the master for another materialized view is called a master materialized view. In this case, the CREATE MATERIALIZED VIEW statement that creates the orders materialized view has a subquery with a many to one relationship, because there can be many orders for each customer. The materialized view created by this statement is fast refreshable and updatable. "string" Cause: There was no materialized view log on the master table. You cannot create refresh-on-commit materialized views based on a master with user-defined types or Oracle-supplied types. Reside in a different database than the materialized view group at its master materialized view site. For example, the following SQL statement creates the categories_typ user-defined type: When you create an object table based on this type, you can either specify that the object identifier should be system-generated or primary key-based: When you create a materialized view log on an object table, you must log the object identifier by specifying the WITH OBJECT ID clause, but you can also specify that the primary key is logged if the object identifier is primary key-based. If a materialized view does not belong to a materialized view group, then it must be a read-only or writeable materialized view. Oracle supports the creation of materialized views with collection columns. Such a materialized view log supports primary key, ROWID, and object materialized views, which is helpful for environments that have all three types of materialized views based on a master. These materialized views at the national level only replicate the subset of data from the master tables that apply to their respective countries. The type of materialized view you create determines how the materialized view is refreshed and used by query rewrite. Figure 3-1 Materialized View Connected to a Single Master Site. When you use the UNION operator to create a materialized view, you have two SELECT statements around each UNION operator, one is above it and one is below it. Object ID: The materialized view records changes to the master object table or master object materialized view based on the object identifier of the affected row objects. It seems that snaptime$$ always has the same time. Note that materialized view log tables using primary keys also have rupd$_ tables, as is the case in this example. To view the name of a storage table, query the DBA_NESTED_TABLES data dictionary table. When you create a materialized view log for a master table or master materialized view, Oracle creates an underlying table as the materialized view log. If you do not rescope the REF column, then the materialized view retains the REF scope of the master. You can create materialized view logs on object tables. If new inventories that are greater than zero are identified for products in the order_items table, then the new data will be propagated to the materialized view site during the subsequent refresh process. Figure 3-13 Refresh Groups Can Contain Objects from Multiple Materialized View Groups. Though you have the option of automating the refresh process by scheduling a job, you can manually refresh your materialized view on-demand, which is an ideal solution for sales applications running on a laptop. A materialized view is a transactionally (read) consistent reflection of its master as the data existed at a specific point in time (that is, at creation or when a refresh occurs). Changes made to the master table or master materialized view, as recorded by the materialized view log, are propagated to the materialized view during the refresh process. SEQUENCE Specify SEQUENCE to indicate that a sequence value providing additional ordering information should be recorded in the materialized view log. Figure 3-10 Materialized View Replication Objects. A scoped REF requires less storage space and provides more efficient access than an unscoped REF. This chapter, and this Oracle Database Advanced Replication manual in general, discusses materialized views for use in a replication environment. 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. Conversely, you can omit scheduling information so that the refresh group must be refreshed manually or "on-demand." To avoid conflicting names, you can append the group owner name to the end of your object name. Oracle is optimized for large refresh groups. Materialized views that are based on other materialized views can be read-only or updatable. Also, large refresh groups enable you to refresh a greater number of materialized views with only one call to the replication management API. A master table can have only one materialized view log defined on it. Consider a replication environment with the following characteristics: Master site orc1.example.com has the oe.customers table. After the required types are created at the materialized view site, you can create an object materialized view by specifying the OF type clause. The update for the credit_limit at the orc1.example.com site is recorded in both the deferred transaction queue and the materialized view log a this master site. To be fast refreshed, the defining query for a materialized view must observe certain restrictions. In Oracle 19c the cache type is always MATERIALIZED. This company has one main office in 14 countries and many regional offices for cities in these countries. All join columns must be included in the materialized view log of the master, even if the subquery is many to one. User-defined types include all types created using the CREATE TYPE statement, including object, nested table, VARRAY, and indextype. Column subsetting enables you to include only the columns that are needed from the master in the materialized views. See the Oracle Database PL/SQL Packages and Types Reference for more information. An object table is a special kind of table in which each row represents an object. Row ID: The materialized view records changes to the master table or master materialized view based on the rowid of the affected rows. Use the WITH clause to indicate whether the materialized view log should record the primary key, rowid, object ID, or a combination of these row identifiers when rows in the master are changed. A special SEQUENCE column can be include in the materialized view log to help Oracle apply updates to materialized view logs in the correct order when a mix of Data Manipulation (DML) commands, e.g. Invalid rowid hints can cause performance problems. If the materialized view site is a master materialized view site, then it contains the mechanisms described in the previous section in addition to the mechanisms described in this section. Use the force setting when you want a materialized view to refresh if a fast refresh is not possible. ROWID materialized views can be used for materialized views based on master tables that do not have a primary key, or for materialized views that do not include all primary key columns of the master tables. Almost certainly so. Oracle Database creates the materialized view log in the schema of its master table. For example, the following statement creates a materialized view log for the categories_tab_sys object table and specifies that the object identifier column be logged: The following statement creates a materialized view log for the categories_tab_pkbased object table and specifies that the primary key column be logged along with the object identifier column: Materialized view logs are exported with the schema name explicitly given in the DDL statements. If the connectivity is lost or interrupted during the refresh, then all changes are rolled back so that the database remains consistent. Users cannot perform data manipulation language (DML) statements on read-only materialized views, but they can perform DML on updatable and writeable materialized views. The materialized view log is created in the same schema as the target master. This process is called incremental or fast refresh. For example, the master for the level 2 materialized view orders_2 is the level 1 materialized view orders_1. Read-only materialized views use many of the same mechanisms as updatable materialized views, except that they do not need to belong to a materialized view group. This section assumes a basic understanding of the information in that book. For example, suppose a salesperson wants to see all of the customers who have an order with an order total greater than $20,000, then the most efficient method is to create a materialized view with a one to many subquery in the defining query of a materialized view. The process of setting up a materialized view is sometimes called materialization. Do not allow any database manipulation language (DML) changes on the updatable materialized views until you have finished the administration operation on the master site and regenerated replication support for the materialized view. The company uses the tables in the hr schema to maintain the employee information. The nested_table_storage_clause is optional. The following sections explain the privileges requirements in detail. Consequently, REFs to the rows in the object table remain valid at the materialized view site. Row subsetting enables you to include only the rows that are needed from the master in the materialized views by using a WHERE clause. You use the BEGIN_TABLE_REORGANIZATION and END_TABLE_REORGANIZATION procedures in the DBMS_MVIEW package to reorganize a master table. 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. To accommodate multiple materialized view groups at the same materialized view site that are based on a single replication group at the master site or master materialized view site, you can specify a group owner as an additional identifier when defining your materialized view group. The arrows in Figure 3-7 represent database links. They are updatable if the materialized view was created as part of a materialized view group and FOR UPDATE was specified when defining the materialized view. Therefore, if any changes where made to the master since the last refresh, then a materialized view refresh takes some time to apply the changes to the materialized view. 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. The ability to create materialized views that are based on other materialized views enables you to create multitier materialized views. Otherwise, the normal rules for connections through database links apply. Updatable materialized view is useful if you are looking to replicate the changes happened on the client site to the master site. The outermost SELECT list columns do not match for the queries in the UNION. However, in some replication environments, different users perform these operations on a particular materialized view. If you refresh regularly and can sacrifice query performance, then use Method B (simple materialized view). 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. Therefore, you use the WITH ROWID clause to specify a rowid hint. In this scenario, the hr.employees master table is at headquarters in the United States and each regional office has a an hr.employees materialized view that only contains the necessary employee information. You can use the UNION operator as a way to create fast refreshable materialized views that satisfy "or" conditions without using the OR expression in the WHERE clause of a subquery. Under no circumstances, however, could Group B at the materialized view site contain objects from Group A at the master site. CREATE MATERIALIZED VIEW, ALTER MATERIALIZED VIEW, Oracle Database Concepts, Oracle Database Data Warehousing Guide, and Oracle Database Advanced Replication for information on materialized views in general, ALTER MATERIALIZED VIEW LOG for information on modifying a materialized view log, DROP MATERIALIZED VIEW LOG for information on dropping a materialized view log, Oracle Database Utilities for information on using direct loader logs. To decrease the amount of data that is replicated, a materialized view can be a subset of a master table or master materialized view. Similarly, if a customer's credit limit drops to less than $10,000, then the customer's data will be removed from the materialized view during the subsequent refresh process. Oracle uses materialized views (also known as snapshots in prior releases) to replicate data to nonmaster sites in a replication environment and to cache expensive queries in a data warehouse environment. Materialized views are updated through an efficient batch process from a single master site or master materialized view site. That is, an object materialized view is composed of row objects. If the master has a system generated OID, then the OIDs of row objects in the materialized view are system generated. You can use this clause to avoid the overhead of recording new values. Therefore, in cases where the network connectivity is difficult to maintain, consider using smaller refresh groups. This clause also specifies whether the materialized view log records additional columns that might be referenced as filter columns, which are non-primary-key columns referenced by subquery materialized views, or join columns, which are non-primary-key columns that define a join in the subquery WHERE clause. Here, an inventory is a certain quantity of a product at a particular warehouse. Combination: The materialized view records changes to the master table or master materialized view based any combination of the three options. If the creator of a materialized view also owns the materialized view, then this user must have the following privileges to create a materialized view, granted either explicitly or through a role: CREATE MATERIALIZED VIEW or CREATE ANY MATERIALIZED VIEW. Materialized views do not require a dedicated network connection. Specify the schema containing the materialized view log master table. If this log is for a table on which you have a single-table materialized aggregate view, and if you want the materialized view to be eligible for fast refresh, then you must specify INCLUDING. For example, consider a company with international, national, and local offices. If you own the master table, then you can create an associated materialized view log if you have the CREATE TABLE privilege. It cannot replicate some attributes of a column object but not others. In addition, an updatable materialized view must reside in a different database than the master replication group. For certain applications, you might want to consider using a complex materialized view. The following are restrictions for fast refresh materialized views with unions containing subqueries: All of the restrictions described in the previous section, "Restrictions for Materialized Views with Subqueries", apply to the subqueries in each union block. PRIMARY KEY Specify PRIMARY KEY to indicate that the primary key of all rows changed should be recorded in the materialized view log. The creator's privileges can be granted explicitly or through a role, but the owner's privileges must be granted explicitly. That is, the following statement creates a materialized view that contains orders for customers whose credit limit is greater than $10,000: Figure 3-3 Row Subsetting with Many to One Subqueries. The updatable materialized view log is also used when you fast refresh a writeable materialized view, as illustrated in the following scenario: A user inserts a row into a writeable materialized view that has a remote master. Primary key columns are implicitly recorded in the materialized view log. Restriction on Master Tables of Materialized View Logs, Creating a Materialized View Log: Examples, Specifying Filter Columns for Materialized View Logs: Example, Specifying Join Columns for Materialized View Logs: Example, Including New Values in Materialized View Logs: Example, Description of the illustration create_materialized_vw_log.gif, Description of the illustration physical_attributes_clause.gif, Description of the illustration logging_clause.gif, Description of the illustration parallel_clause.gif, Description of the illustration new_values_clause.gif, "Creating a Materialized View Log: Examples", "Specifying Filter Columns for Materialized View Logs: Example", "Specifying Join Columns for Materialized View Logs: Example", "Including New Values in Materialized View Logs: Example", "Creating Materialized Aggregate Views: Example", "Creating a Fast Refreshable Materialized View: Example". Materialized view logs do not support columns that have been encrypted using transparent data encryption. When you are using multitier materialized views, the materialized view based on a master table is called a level 1 materialized view. The default is NOCACHE. Including New Values in Materialized View Logs: Example The following example creates a materialized view log on the oe.product_information table that specifies INCLUDING NEW VALUES: You could create the following materialized aggregate view to use the product_information log: This materialized view is eligible for fast refresh because the log defined on its master table includes both old and new values. However, you can use row subsetting on the parent table of a nested table and doing so can result in a subset of the nested tables in the materialized view. 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. If you drop orders_lev1, orders_lev2 remains intact. The following materialized view is created with a WHERE clause containing a subquery: This type of materialized view is called a subquery materialized view. After you have defined your materialized view group with the addition of a group owner, you add your materialized view objects to the target materialized view group by defining the same group owner. If you have updatable multitier materialized views, then DML changes made to the multitier materialized view can be pulled back to this materialized view multiple times to ensure data consistency after each refresh of a materialized view. The subquery must be a positive subquery. Following are the types of materialized view logs: Primary Key: The materialized view records changes to the master table or master materialized view based on the primary key of the affected rows. The following statement creates the hr.employees materialized view for the United Kingdom office. Ensure that you account for the extra space required by these logs when you are planning for your master materialized view site. A materialized view log can also contain other columns to support fast refreshes of materialized views with subqueries. The query rewrite mechanism in the Oracle server automatically rewrites the SQL query to use the summary tables. PCT is also used to support fast refresh after partition maintenance operations on a materialized view's master table. 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. The defining query of a materialized view with a subquery is subject to several restrictions to preserve the materialized view's fast refresh capability. Though the difference between materialized view logs based on primary keys and rowids is small (one records affected rows using the primary key, while the other records affected rows using the physical rowid), the practical impact is large. Materialized Views in Oracle. Group A at the materialized view site (see Figure 3-12) contains only some of the objects in the corresponding Group A at the master site. 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. For example, suppose a materialized view named orders_lev1 is based on the oe.orders master table, and a materialized view named orders_lev2 is based on orders_lev1. One configuration that you want to avoid is using multiple refresh groups to refresh the contents of a single materialized view group. 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. Using either a fast refresh uses materialized view log groups a and B at the master for the.. With materialized views that do materialized view log in oracle 11g with example rescope the REF is an Oracle object that occupies a column! Those created using the for update clause but is not part of a materialized view log section ``. Both the primary key materialized views based on one level 1 materialized view instead of the described... 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