we are working on data migration of sql server 2000 to Oracle 11g. Sql server has 4 databases which has to be migrated. These 4 databases are used for 6 different standalone applications. Oracle is installed in Unix server. Can we create a single database and different schemas for each sql server database or do I need to create multiple databases or can I use single database, single schema and multiple tablespaces or any other procedure to maintain the performance?
You can create multiple Oracle databases. Or you can create a single database with multiple schemas. Or you can create a single database with a single schema an put everything there if all your object names are unique.
The most similar approach would generally be to create a single Oracle database with four schemas. That gives you four separate namespaces in case you have objects in two different SQL Server databases that have the same name. And a single Oracle database per server generally gives the best performance since you're not allocating multiple SGAs and PGAs in memory or running multiple sets of background processes.
Tablespaces in Oracle are a completely separate concept. They have nothing to do with namespaces or permissions. They simply allow you to determine which objects reside in which physical data files. Barring something extremely unusual, tablespaces have nothing to do with performance. You could have the objects in all four schemas use a single tablespace. Or you could create four separate tablespaces. Or you could create multiple tablespaces that each have objects from different schemas. My guess is that the simplest approach is to create one tablespace per schema so that you can manage each application's disk space allocation separately.
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I'm looking for the best (best practice) option for one way replication between two databases. I would like to keep this purely SQL but, can write something in C# or use an ETL tool if there are no other good options.
Current setup:
DB1 - There are three instances of this database. It is a large relational database, the schema is the same for each but, they are separate data pots (no replication). Two databases on a 2012 server and one on a 2014 server
DB2 - There are two instances of this database on seperate servers (Europe, Americas) and the data is merge replicated between the two. The publisher is the 2014 server.
The Goal:
DB2 is tied to some reports. It has one table and a small application attached to that table. Users from many different countries enter data via a small application into DB2 and generate reports out of the application.
DB1 is a relational database that has a very large application on top of it but with fewer users. If users are using the application for DB1 then they should not need to duplicate their records into DB2.
There should be one-way replication from the multiple seperate DB1s into DB2. How quickly this happens is not too important.
The important things are:
No backwards replication occurs from DB2s > DB1s (Data only flows from DB1s into one of the DB2s)
Create, Update, and Delete actions should occur in DB2 based on the results
of a comparisson with DB1 (the one way replication)
Current Approach:
I currently have a flat sql view on each DB1 database that has the same schema as the table in the DB2 db's that the data needs to go into.
The servers are also joined as linked servers.
My though was to do a sort of manually written replication script on one of the DB2 databases that calls the views from the DB1s and does the CUD actions on a timed basis.
It seems to me that there should be an easier way though!?
Any thoughts on how to do this would be very much appreciated.
Keep in mind that since several of the DB1s exist on a SQL 2012 server that there may be some issues as 2012 might not be allowed to be a publisher for replication to a 2014 server.
I've recently had to do some work on an Oracle database. I come from a MS SQL background. I am still trying to get my head around some basic definitions in Oracle
Schema - to me this just meant the structure of the database. Which includes the structure of the tables, indexes and any constrains. This does NOT include any data that is stored in the tables. A database would only contain one Schema and one set of data.
But in Oracle it seems like a Schema is defined as the structure and the data. And a database can hold many Schemas.
Is that accurate?
Regardless of the database engine, it isn't uncommon to talk about your data model as your "schema". That's not necessarily how any relational database engine defines the term but it may be perfectly clear from the context that you're talking only about the definitions of objects and not the actual data.
In both SQL Server and Oracle, a "schema" is a way of collecting together a bunch of related objects, code, and data. If you define a schema in SQL Server and create a table foo in that schema along with a usp_setFoo procedure, the data that is in foo would be part of that schema. In the same way, an Oracle schema would generally involve table and index definitions, data, code, etc.
Technically, in Oracle, a schema is defined as the set of objects owned by a particular user. Practically, an Oracle schema is generally roughly analogous to a SQL Server "database". Oracle normally has two levels of object naming (schema.object) rather than three levels in SQL Server (database.schema.object). If you're using the enterprise edition of Oracle 12.1 with pluggable databases, that changes things a bit and an Oracle pluggable database can be similar to a SQL Server database.
Ive run into the issue where I need to query 2 separate databases(same instance) in one query.
I am used to doing this with mysql, but Im not sure how to do it with DB2.
In mySQL it would be something like:
SELECT user_info.*, game.*
FROM user_info, second_db.game_stats as game
WHERE user_info.uid = game.uid
So the question is how i translate a query like that into DB2 syntax?
Equivalent of this
Is there a reason why you have the tables in a separate database? MySQL doesn't support the concept of schemas, because in MySQL a "schema" is the same thing as a "database". In DB2, a schema is simply a collection of named objects that lets you group them together.
In DB2, a single database is much closer to an entire MySQL server, as each DB2 database can have multiple schemas. With multiple schemas inside the same database, your query can run more or less unchanged from how it is written.
However, if you really have 2 separate DB2 databases (and, for some reason, don't want to migrate to a single database with multiple schemas): You can do this by defining a nickname in your first database.
This requires a somewhat convoluted process of defining a wrapper (CREATE WRAPPER), a server (CREATE SERVER), user mapping(s) (CREATE USER MAPPING) and finally the nickname (CREATE NICKNAME). It is generally easiest to do these tasks using the Control Center GUI because it will walk you through the process of defining each of these.
I have the following scenario
I have 4 different (sql server) databases (legacy), one for each geo (NA,AP,LA,EMEA). The schema is the same in all the db's.
I am in the process of creating a front-end which will go across 4 different db's based on the users selection.I am thinking of using Entity framework. The db's are on different servers. What is the best way to create the entities? should i create 4 different edmx? there will be scenarios when the users results need to come from one or more db's
Thanks,
Nagendra
If databases are exactly same you can create edmx file only for one of databases (the mapping will be same for all DBs) and use 4 ObjectContext instances with different connection strings. The problem here can be with your second requirement. Querying more DBs means that you have to query each DB separately and merge/union results in memory on the application server. So such scenario is not very good for advanced querying where you need to run complex queries on all databases at the same time.
What is the importance of schema in sql server?
Where this schema help me?
Is it important for security reasons?
Yes, the primary purpose of SQL schema was -is- to facilitate security management: define who [which principals] can access what [which database objects]. This was made particularly easier starting with SQL 2005 when the schema stopped being directly tied to the owner.
Another use of schema is to serve as a namespace, that is preventing name clashes between objects from different schemas.
The original use of this was to allow multiple [interactive, i.e. ad-hoc like] users of a given database to create their own tables or stored procedures (or other objects), without having to worry about the existence of similarly named objects possibly introduced by other users.
The Namespace-like nature of schema can also be put to use in a planned database setting, i.e. one when a single architect designs the database structure in a way which provides distinct type of access, and indeed different behaviors, for distinct user groups.
They partition your database to make management easier.
This is from MSDN:
A schema is now a distinct namespace
that exists independently of the
database user who created it. In other
words, a schema is simply a container
of objects. A schema can be owned by
any user, and its ownership is
transferable.
Here's the page that came from: http://msdn.microsoft.com/en-us/library/ms190387.aspx
In relation to security it makes it simpler to assign permissions as you can grant someone access to a schema without exposing your entire database to them.
What a schema is changed with the release of SQL Server 2005 and later - I think of it as an additional security layer as well as a container of objects.
This is quite a good resource:
http://msdn.microsoft.com/en-us/library/ms190387(SQL.90).aspx
Schema is mainly used to Manage several logical entities in one physical database.
Schemas offer a convenient way to separate database users from database object owners. They give DBA’s the ability to protect sensitive objects in the database, and also to group logical entities together.
This is especially advantageous in situations where those objects are often utilized as a unit by applications. For example, a hotel-management system may be broken down into the following logical entities or modules: Rooms, Bar/Restaurant, and Kitchen Supplies.
These entities can be stored as three separate physical databases. Using schemas however, they can be combined as three logical entities in one physical database. This reduces the administrative complexity of managing three separate databases.
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