ALTER MATERIALIZED VIEW LOG
Purpose
A materialized view log is a table associated with the master table of a materialized view. Use the ALTER
MATERIALIZED
VIEW
LOG
statement to alter the storage characteristics or type of an existing materialized view log.
Note:
The keyword SNAPSHOT
is supported in place of MATERIALIZED
VIEW
for backward compatibility.
See Also:
-
CREATE MATERIALIZED VIEW LOG for information on creating a materialized view log
-
ALTER MATERIALIZED VIEW for more information on materialized views, including refreshing them
-
CREATE MATERIALIZED VIEW for a description of the various types of materialized views
Prerequisites
You must be the owner of the master table, or you must have the READ
or SELECT
privilege on the master table and the ALTER
privilege on the materialized view log.
See Also:
Oracle Database Administrator’s Guide for detailed information about the prerequisites for ALTER
MATERIALIZED
VIEW
LOG
Syntax
alter_materialized_view_log::=
(physical_attributes_clause::=, add_mv_log_column_clause::=, alter_table_partitioning::= (in ALTER
TABLE
), parallel_clause::=, logging_clause::=, allocate_extent_clause::=, shrink_clause::=, move_mv_log_clause::=, mv_log_augmentation::=, mv_log_purge_clause::=, for_refresh_clause::=)
add_mv_log_column_clause::=
allocate_extent_clause::=
shrink_clause::=
move_mv_log_clause::=
mv_log_augmentation::=
new_values_clause::=
mv_log_purge_clause::=
for_refresh_clause::=
Semantics
FORCE
If you specify FORCE
and any items specified with the ADD
clause have already been specified for the materialized view log, then Oracle Database does not return an error, but silently ignores the existing elements and adds to the materialized view log any items that do not already exist in the log. Likewise, if you specify INCLUDING
NEW
VALUES
and that attribute has already been specified for the materialized view log, Oracle Database ignores the redundancy and does not return an error.
schema
Specify the schema containing the master table. If you omit schema
, then Oracle Database assumes the materialized view log is in your own schema.
table
Specify the name of the master table associated with the materialized view log to be altered.
physical_attributes_clause
The physical_attributes_clause
lets you change the value of the PCTFREE
, PCTUSED
, and INITRANS
parameters and the storage characteristics for the materialized view log, the partition, the overflow data segment, or the default characteristics of a partitioned materialized view log.
Restriction on Materialized View Log Physical Attributes
You cannot use the storage_clause
to modify extent parameters if the materialized view log resides in a locally managed tablespace. Refer to CREATE TABLE for a description of these parameters.
add_mv_log_column_clause
When you add a column to the master table of the materialized view log, the database does not automatically add a column to the materialized view log. Therefore, use this clause to add a column to the materialized view log. Oracle Database will encrypt the newly added column if the corresponding column of the master table is encrypted.
alter_table_partitioning
The syntax and general functioning of the partitioning clauses is the same as described for the ALTER
TABLE
statement. Refer to alter_table_partitioning in the documentation on ALTER
TABLE
.
Restrictions on Altering Materialized View Log Partitions
Altering materialized view log partitions is subject to the following restrictions:
-
You cannot use the
LOB_storage_clause
ormodify_LOB_storage_clause
when modifying partitions of a materialized view log. -
If you attempt to drop, truncate, or exchange a materialized view log partition, then Oracle Database raises an error.
parallel_clause
The parallel_clause
lets you specify whether parallel operations will be supported for the materialized view log.
For complete information on this clause, refer to parallel_clause in the documentation on CREATE
TABLE
.
logging_clause
Specify the logging attribute of the materialized view log. Refer to the logging_clause for a full description of this clause.
allocate_extent_clause
Use the allocate_extent_clause
to explicitly allocate a new extent for the materialized view log. Refer to allocate_extent_clause for a full description of this clause.
shrink_clause
Use this clause to compact the materialized view log segments. For complete information on this clause, refer to shrink_clause in the documentation on CREATE
TABLE
.
move_mv_log_clause
Use the MOVE
clause to move the materialized view log table to a different tablespace, to change other segment or storage attributes of the materialized view log, or to change the parallelism of the materialized view log.
Restriction on Moving Materialized View Logs
The ENCRYPT
clause of the storage_clause
of segment_attributes
is not valid for materialized view logs.
CACHE | NOCACHE Clause
For data that will be accessed frequently, CACHE
specifies that the blocks retrieved for this log are placed at the most recently used end of the LRU list in the buffer cache when a full table scan is performed. This attribute is useful for small lookup tables. NOCACHE
specifies that the blocks are placed at the least recently used end of the LRU list. Refer to "CACHE | NOCACHE | CACHE READS" in the documentation on CREATE
TABLE
for more information about this clause.
mv_log_augmentation
Use the ADD
clause to augment the materialized view log so that it records the primary key values, rowid values, object ID values, or a sequence when rows in the materialized view master table are changed. This clause can also be used to record additional columns.
To stop recording any of this information, you must first drop the materialized view log and then re-create it. Dropping the materialized view log and then re-creating it forces a complete refresh for each of the existing materialized views that depend on the master table on its next refresh.
Restriction on Augmenting Materialized View Logs
You can specify only one PRIMARY
KEY
, one ROWID
, one OBJECT
ID
, one SEQUENCE
, and each column in the column list once for each materialized view log. You can specify only a single occurrence of PRIMARY
KEY
, ROWID
, OBJECT
ID
, SEQUENCE
, and column list within this ALTER
statement. Also, if any of these values was specified at create time (either implicitly or explicitly), you cannot specify that value in this ALTER
statement unless you use the FORCE
option.
Specify OBJECT
ID
if you want the appropriate object identifier of all rows that are changed to be recorded in the materialized view log.
Restriction on the OBJECT ID clause
You can specify OBJECT
ID
only for logs on object tables, and you cannot specify it for storage tables.
Specify PRIMARY
KEY
if you want the primary key values of all rows that are changed to be recorded in the materialized view log.
Specify ROWID
if you want the rowid values of all rows that are changed to be recorded in the materialized view log.
SEQUENCE
Specify SEQUENCE
to indicate that a sequence value providing additional ordering information should be recorded in the materialized view log.
column
Specify the additional columns whose values you want to be recorded in the materialized view log for all rows that are changed. Typically these columns are filter columns (non-primary-key columns referenced by subquery materialized views) and join columns (non-primary-key columns that define a join in the WHERE
clause of the subquery).
See Also:
-
CREATE MATERIALIZED VIEW for details on explicit and implicit inclusion of materialized view log values
-
Oracle Database Administrator’s Guide for more information about filter columns and join columns
The NEW
VALUES
clause lets you specify whether Oracle Database saves both old and new values for update DML operations in the materialized view log. The value you set in this clause applies to all columns in the log, not only to columns you may have added in this ALTER
MATERIALIZED
VIEW
LOG
statement.
INCLUDING
Specify INCLUDING
to save both new and old values in the log. 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
.
EXCLUDING
Specify EXCLUDING
to disable the recording of new values in the log. You can use this clause to avoid the overhead of recording new values.
If you have a fast-refreshable single-table materialized aggregate view defined on this table, then do not specify EXCLUDING
NEW
VALUES
unless you first change the refresh mode of the materialized view to something other than FAST
.
mv_log_purge_clause
Use this clause alter the purge attributes of the materialized view log in the following ways:
-
Change the purge from
IMMEDIATE
SYNCHRONOUS
toIMMEDIATE
ASYNCHRONOUS
or fromIMMEDIATE
ASYNCHRONOUS
toIMMEDIATE
SYNCHRONOUS
-
Change the purge from
IMMEDIATE
to scheduled or from scheduled toIMMEDIATE
-
Specify a new start time and a new
next
time andinterval
If you are altering purge from scheduled to IMMEDIATE
, then the scheduled purged job associated with that materialized view log is dropped. If you are altering purge from IMMEDIATE
to scheduled, then a purge job is created with the attributes provided. If you are altering scheduled purge attributes, then only those attributes specified will be changed in the scheduler purge job.
You must specify FORCE
if you are altering log purge to its current state (that is, you are not making any change), unless you are changing scheduled purge attributes.
To learn whether the purge time or interval has already been set for this materialized view log, query the *_MVIEW_LOGS
data dictionary views. See the CREATE
MATERIALIZED
VIEW
LOG
clause mv_log_purge_clause for the full semantics of this clause.
for_refresh_clause
Use this clause to change the refresh method for which the materialized view log will be used.
FOR SYNCHRONOUS REFRESH
Specify this clause to change from fast refresh to synchronous refresh, or complete refresh to synchronous refresh. A staging log will be created.
If you are changing from fast refresh, then ensure that the following conditions are satisfied before using this clause:
-
All changes in the materialized view log have been consumed.
-
Any refresh-on-demand materialized views associated with the master table have been refreshed.
-
Any refresh-on-commit materialized views associated with the master table have been converted to refresh-on-demand materialized views.
After you use this clause, you cannot perform DML operations directly on the master table. You must use the procedures in the DBMS_SYNC_REFRESH
package to prepare and execute change data operations.
FOR FAST REFRESH
Specify this clause to change from synchronous refresh to fast refresh, or complete refresh to fast refresh. A materialized view log will be created.
If you are changing from synchronous refresh to fast refresh, then ensure that all changes in the staging log have been consumed before using this clause.
After you use this clause, you can perform DML operations directly on the master table.
See the CREATE
MATERIALIZED
VIEW
LOG
clause for_refresh_clause for the full semantics of this clause.
Examples
Rowid Materialized View Log: Example
The following statement alters an existing primary key materialized view log to also record rowid information:
ALTER MATERIALIZED VIEW LOG ON order_items ADD ROWID;
Materialized View Log EXCLUDING NEW VALUES: Example
The following statement alters the materialized view log on hr.employees
by adding a filter column and excluding new values. Any materialized aggregate views that use this log will no longer be fast refreshable. However, if fast refresh is no longer needed, this action avoids the overhead of recording new values:
ALTER MATERIALIZED VIEW LOG ON employees ADD (commission_pct) EXCLUDING NEW VALUES;