Oracle as a Data Source
December 23, 2009
The Oracle RDBMS is obviously a data source for itself, and when a user wants to get data from the database, there is a litany of features and options to consider. Permissions, roles, grants, tables, views, synonyms and database links are commonly seen. Perhaps less obvious are other data sources within the database, and one in particular is the materialized view (or snapshot in older days). In this article, well take a quick look at the materialized view and extend the concept of that feature to a case when Oracle is the data source for another relational database management system.
Ignoring the initial setup, how is a materialized view populated, updated or refreshed? You have several options, with the two extremes ranging from do it when I say so (ON DEMAND) to do it whenever a change is made (ON COMMIT). The what in where the change is made (or being pulled from) is known as a master table (or a detail table if dealing with a data warehouse). The database source is also then known as the master database as it contains the master tables.
When managing materialized views, some of the privileges required include CREATE MATERIALIZED VIEW (for working within your own schema) and CREATE ANY MATERIALIZED VIEW (for creating these in other schemas). If query rewrite is involved, then QUERY REWRITE is necessary at your own level and GLOBAL QUERY REWRITE if working outside your schema. Just by being able to create objects in your own schema implies a slew of object privileges.
Now, what if the Oracle RDBMS, or more specifically, an Oracle database, serves as the master database for another database system? What privileges would be necessary within Oracle (for a given schema) in order to push data to say, a SQL Server database? If data can be pushed from Oracle into SQL Server, then you wouldnt be wrong in assuming that data can be pushed from SQL Server into Oracle. In SQL Server terminology, the Oracle database is referred to as either the publisher or subscriber, and the direction in which data flows (from SQL Servers perspective) is known as a publication or subscription.
Starting with Oracle as the publisher (data being pushed from Oracle to MSSQL), what is needed on the Oracle RDBMS side of things? The process (from MSSQLs side) can be looked at as creating a replication user within Oracle. Its not all that exotic in terms of what is granted to the Oracle user/schema, and the list of grants includes:
Microsoft provides a script to perform these steps, and the script (oracleadmin.sql) can be found in the
<drive>:\Program Files\Microsoft SQL Server\<InstanceName>\MSSQL\Install
folder. The InstanceName part of the path may be confusing if youre not familiar with the installation footprint of SQL Server, but to make it simple, if all youve installed is the MSSQL server software for the instance (which contains multiple databases), then InstanceName is likely to be MSSQL.1.
In the folder listing above, the 80, 90 and 100 are related to versioning of SQL Server, with 80 corresponding to SQL Server 2000, 90 for 2005, and 100 for 2008. The MSSQL.X folders relate to what was installed feature-wise. In the example above, the 2 and 3 correspond to Analysis Services and Reporting Services, and the order can go either way: it just depends on which feature was installed first/in a later configuration run.
In the script provided by Microsoft, the Oracle user is referred to as a replication user because that is essentially what is taking place here: data is being replicated from Oracle to SQL Server. If the replication user is the conduit through which data from Oracle flows into SQL Server, what other privilege do you think may be needed for this user? Data changes in schema X, but how does the replication user know that in terms of being able to see the data in the other schema? Reading the script is useful here because a comment at the end tells us what else is needed: the replication user needs to have select privileges on the other tables. If you want a table in the Scott schema to be replicated into a database in a SQL Server instance, then Scott needs to have granted select on that table to the replication user.
The replication user in Oracle winds up with the following collection of objects once the SQL Server setup is complete (to be covered in a subsequent article). The count by object type is:
All of the object names are prefaced with HREPL, which suggest heterogeneous replication, which makes sense since the sources are different. A complete listing of the objects and their function or purpose can be found in the Books Online documentation. Much of what is created in the replication user schema is analogous to how Oracle operates materialized views.
The list of steps provided by Microsoft include:
For Step 1, running the oracleadmin script is quick and it exits at the end. My example uses MSSQLDIST/oracle for the replication user and password, and the USERS tablespace as the default tablespace. For Step 2, use a convenient schema such as SCOTT and issue (as Scott):
grant select on dept to mssqldist; grant select on emp to mssqldist; grant select on bonus to mssqldist; grant select on salgrade to mssqldist;
For Step 3, install the Administrator level version of Oracle client software (no need to bother with any other level) on the SQL Server host. Being Windows, this is a very straightforward process.
Step 4 will be covered in part two, as it is a bit more involved. One of the gotchas in this process is the version of SQL Server being used. A non-SQL Server publisher is supported only in the Enterprise and Developer editions. If using the standard edition, then sorry, you will be out of luck when at the final click OK steps of configuring the publisher.
Once the configuration for replication is complete, it is interesting to see data flow back and forth between two different database systems. Oracle software is entirely free for educational (your own, that is) purposes, and SQL Server is free for a while (180 day evaluation period). The download for SQL Server 2005 is here, and the page contains links to getting 2008. If you are running Windows XP Professional on a personal computer, along with a decent amount of memory (if you can run Oracle okay, you can run SQL Server as well), you have enough to get started on configuring replication between Oracle and SQL Server, and part two will go into more detail about this process.