Database ReadWriteModes

Artykuł
02/13/2015

There are often situations when an Analysis Services database administrator (dba) wants to change a read/write database to a read-only database, or vice versa. These situations are often driven by business needs, such as sharing the same database folder among several servers for scaling out a solution and improving performance. For these situations, the ReadWriteMode database property enables the Analysis Services dba to easily change the database operating mode.

ReadWriteMode database property

The ReadWriteMode database property specifies whether the database is in read/write mode or in read-only mode. These are the only two possible values of the property. When the database is in read-only mode, no changes or updates can be applied to the database. However, when the database is in read/write mode, changes and updates can occur. The ReadWriteMode database property is defined as a read-only property; it can only be set through an Attach command.

When a database is in read-only mode, certain restrictions are in place that affect the ordinary set of allowed operations to the database. See the following table for the restricted operations.

ReadOnly mode	Restricted operations
XML/A commands [!UWAGA] An error is raised when you execute any one of these commands.	Create Alter Delete Process MergePartitions DesignAggregations CommitTransaction Restore Synchronize Insert Update Drop [!UWAGA] Cell writeback is allowed in databases set to read-only; however, the changes cannot be committed.
MDX statements [!UWAGA] An error is raised when you execute any one of these statements.	COMMIT TRAN CREATE SESSION CUBE ALTER CUBE ALTER DIMENSION CREATE DIMENSION MEMBER DROP DIMENSION MEMBER ALTER DIMENSION [!UWAGA] Excel users cannot use the grouping feature in Pivot tables, because that feature is internally implemented by using CREATE SESSION CUBE commands.
DMX statements [!UWAGA] An error is raised when you execute any one of these statements.	CREATE [SESSION] MINING STRUCTURE ALTER MINING STRUCTURE DROP MINING STRUCTURE CREATE [SESSION] MINING MODEL DROP MINING MODEL IMPORT SELECT INTO INSERT UPDATE DELETE
Background operations	Any background operations that would modify the database are disabled. This includes lazy processing and proactive caching.

ReadWriteMode Usage

The ReadWriteMode database property is to be used as part of an Attach database command. The Attach command allows the database property to be set to either ReadWrite or ReadOnly. The ReadWriteMode database property value cannot be updated directly because the property is defined as read-only. Databases are created with the ReadWriteMode property set to ReadWrite. A database cannot be created in read-only mode.

To switch the ReadWriteMode database property between ReadWrite and ReadOnly, you must issue a sequence of Detach/Attach commands.

All database operations, with the exception of Attach, keep the ReadWriteMode database property in its current state. For example, operations like Alter, Backup, Restore, and Synchronize preserve the ReadWriteMode value.