we are using .net mvc and sqlserver db.
EDIT
We are also using NHibernate for data access. I mention this because we will not be writing our own sql or do stored procs. triggers in the db might work but I don't know if you can do that between databases.
END EDIT
we want to have a multi tenant set up so each client has there own instance of the db. However, we need to have each tenant connect to an other database which has a great deal of user information. there will be some small amount of shared data between them. Basically the tenants will be referencing the data of the users in the shared database.
The idea is that some people will use just the shared database ( independent clients ) they then may well be hired by one of the tenant clients. the tenant will then want access to the new employees data in the shared database. Further the employee may leave one tenant and join another or leave one and remain independent and want access to thier data. We could of course have the shared database schema in each tenant and just do a big export import each time some one left or joined but this seems like a lot of trouble too.
I am asking for any advice on how to manage the fact that the tenants will have references to the shared database but no referential integrity. Or if there is an alternate approach or whatever.
Thank you,
Raif
Across databases you have to give up declarative referential integrity (foreign keys). However you can still enforce this (if you think you need to) using after or instead of triggers, or if you control all data manipulation via stored procedures, you can do it there (on insert or update, for example, you can check first, or as part of the modification join to or use EXISTS against the table(s) in other databases to be sure that a valid value is being used).
I've worked with multi-tenant models and there can be huge benefits that are worth the costs (e.g. giving up DRI in some cases). For things that are mostly reference data and that aren't free-text entry, there shouldn't be a whole lot of extra effort required.
Related
Is there a good reason to start a new project in a fresh Snowflake schema vs. a fresh Snowflake database?
I know this sounds like an opinion based question, but I'm trying to get to the technical limitations of one vs. the other.
As far as I can tell, databases & schemas are just like folders and sub-folders. They seem to have no bearing on cost or capability.
I can do:
SELECT *
FROM database1.schemaA.tableX x
JOIN database2.schemaB.tableY y ON y.row_id = x.row_id
So is it all purely syntax and table organization? Or am I missing something?
For simple use cases, you can treat databases and schemas as folders and subfolders. How you set them up is determined on how you want to organise your data and how you want to manage access control.
Access control: the more granular you want to make your access control the more complicated it is to implement and maintain. It's relatively simple to give users access to everything in a database, it's more complicated to give users access to specific schemas within a database and it can get very complicated to give users access to a subset of tables within a schema. Therefore if you have sets of tables that should be accessible to different set of users it is easier if you keep them in different schemas (or databases).
Replication: if you are going to need to replicate data to another Snowflake account (presumably in another region or otherwise you would probably use Sharing not Replication) then bear in mind that replication happens at the database level i.e. you can't replicate specific schemas (or tables or views), the whole database gets replicated. This may influence how you segregate your data between databases
I'm working on a web-based business application where each customer will need to have their own data (think basecamphq.com type model) For scalability and ease-of-upgrades, I'd prefer to have a single database where each customer gets a filtered version of the data. The problem is how to guarantee that they stay sandboxed to their own data. Trying to enforce it in code seems like a disaster waiting to happen. I know Oracle has a way to append a where clause to every query based on a login id, but does Postgresql have anything similar?
If not, is there a different design pattern I could use (like creating a view of each table for each customer that filters)?
Worse case scenario, what is the performance/memory overhead of having 1000 100M databases vs having a single 1Tb database? I will need to provide backup/restore functionality on a per-customer basis which is dead-simple on a single database but quite a bit trickier if they are sharing the database with other customers.
You might want to look into adding Veil to your PostgreSQL installation.
Schemas plus inherited tables might work for this, create your master table then inherit tables into per-customer schemas which provide a company ID or name field default.
Set the permissions per schema for each customer and set the schema search path per user. Use the same table names in each schema so that the queries remain the same.
I am planning to use ASP.NET MVC2 implemented membership system to manage users. Database that uses application should have tables that are related with these users. Is it possible to use two different databases and make relationships (foreign keys) between them or I will have to merge these two databases into one?
Thanks,
Ile
It is NOT possible to put up relationships between databases. You CAN use triggers to ensure relational integrity.
Otherwise I would say: all in one database, put them into different schemata.
I would put membership/roles in a separate database. I don't think having foreign key constraints is that useful. Its better decoupling if you go through the membership API rather than join with the tables directly. The only thing in the membership database you might need to look up often is the username. If thats becomes a performance problem I'd probably just create an lookup table, either in memory or in a lookup table in the other component's database.
I've been tasked with revisiting a database schema we designed and use internally for various ticketing and reporting systems. Currently there exists about 40 tables in one Oracle database schema supporting perhaps six webapps.
However, there's one unifying relationship amongst them all: a rooms table describing the room. Room name, purpose and other data are thrown into a shared table for each app. My initial idea was to pull each of these applications into a separate database, and perform joins between a given database and the room database. But I've discovered this solution prevents foreign key constraints in SQL Server 2005. It seems silly to duplicate one table for each app and keep those multiple copies synchronized.
Should I just leave everything in one large DB, or is there something else I can do separate the tables without losing FK constraints?
The only way to achieve built-in referential integrity is to have the table inside the database in which it is referenced. You might be able to achieve the equivalent of referential integrity using triggers but it would likely be deathly slow.
You might be able to use SQL Server replication, in it's "Transactional replication" mode/form. http://msdn.microsoft.com/en-us/library/ms151176.aspx
if all the apps truly use and depend on the rooms - then keep them all in one DB.
you can still set privilege on the tables properly, and manage the data sets in the non overlapping areas normally -
is there any task you imagine you will not be able to perform when things are together?
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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