There is legacy solution where 2 applications communicate with each other via SQL Server 2008 R2 database table.
Application "A" inserts information to database table from time to time
Application "B" polls database once per second to find out new records
I guess there may be more sophisicated approach how application "B" finds out when new records appear.
It depends on many things that are not explicitly stated in your question. Is that for one table only? For a limited set of tables? For all tables? Do you have full control on both applications?
Let's suppose this is for one table only and you can't modify A application because you don't control its sources. One way would be to use a message queue like described here combined to a trigger on that table.
If you control both applications, don't use the database as a singleton an go for message queues directly ...
Related
. I have two databases in same azure sql server .i want that both database interact to each other using trigger. i.e If any record is inserted in Customer table of first database the trigger gets fired and record is inserted in another database.
We had / have the same problem with triggers that we use for insert-update-delete where we write a record to Database-1 that has the primary table, but also updates Database-2 where we hold "archive" versions of the tables.
The only solution we have identified and are testing is to bring all of the tables into a single database and separate the different tables under separate database schemas in the one database.
Analysis so far of this approach looks promising.
I think what you're trying to do is not allowed in Sql Azure. From my expertise what you are trying to do is a bad practice on-premise as well (think backups-restore and availability issue scenarios).
You should move the dependency in the application and have the application update both databases, as appropriate.
Anyway, if you want to continue with this approach please take a look over Elastic Query feature: https://learn.microsoft.com/en-in/azure/sql-database/sql-database-elastic-query-overview
Please let me know if I can help with something
I’m after a bit of advice on the best way to go about this is SQL server 2008R2 express. I have a number of applications that are in separate databases on the same server. They are all “plugins” that use a central staff/structure list that will be in a separate database. The application is in the process of being migrated from JET.
What I’m looking for is the best way of all the “plugin” databases being able to see the central database and use those tables in standard queries and views etc.
As I’m using express that rules out any replication solution and so far the only option I can think of is to use triggers or a stored procedure to “push” out all the changes to the plugins. The information needs to be populated on a near enough real time basis however the number of changes will be very small maybe up to 100 a day and the biggest table only has about 1000 rows at the moment (the staff names table).
Hopefully that will cover all everything but if anyone needs any more details then just ask
Thanks
Apologies if I've misunderstood, but from your description it sounds like all these databases are hosted on the same instance of SQL Server - it's your mention of replication that makes me uncertain.
Assuming that's the case, you should be able to replace any copies of tables from the central database which are held in the "plugin" databases with views or synonyms which reference the central tables directly, since SQL server allows you to make references between databases on the same server using three-part naming (database_name.schema_name.object_name)
For example, if each plugin db has a table StaffNames, you could replace this with a view by dropping the table, then creating a view:
drop table StaffNames
go
create view StaffNames
as
select * from <centraldbname>.<schema - probably dbo>.StaffNames
go
and your code should continue to work seamlessly, as long as permissions are set up.
Alternatively, you could replace all the references to the shared tables in the plugin databases with three-part name references to the central database, but the view method requires less work.
I have an in house app that has both a Web Interface and a Desktop Interface(is an OCA using Merge Replication). We are still using SQL 2005 and have many 'Archive' tables set up. These are filled by Triggers on there relating Table. tblPersonArchive for tblPerson, etc. To keep the Replication Sets as small as possible I would like to exclude ALL of the Archive tables from replicating.
This shouldn't be an issue from a Business standpoint as that data is never accessed directly by the user's. There is literally no need for it to exist on the Desktop app that is using replication.
What I am trying to figure out, then, is how I accomplish that. My "guess" is that I set the Publication Properties --> Article Properties --> Copy User Triggers = FALSE and then exclude the Archive Tables from the Replication Set. Theoretically the Triggers will still fire, and thus still maintain, the Archive tables through the Web App and on Replication.
Unfortunately, this is only a guess at this point and I was hoping for a little reassurance before plowing in.
Could you not accomplish Publisher only triggers by using the NOT FOR REPLICATION clause in the trigger creation?
We are in the process of a multi-year project where we're building a new system and a new database to eventually replace the old system and database. The users are using the new and old systems as we're changing them.
The problem we keep running into is when an object in one system is dependent on an object in the other system. We've been using views, but have run into a limitation with one of the technologies (Entity Framework) and are considering other options.
The other option we're looking at right now is replication. My boss isn't excited about the extra maintenance that would cause. So, what other options are there for getting dependent data into the database that needs it?
Update:
The technologies we're using are SQL Server 2008 and Entity Framework. Both databases are within the same sql server instance so linked servers shouldn't be necessary.
The limitation we're facing with Entity Framework is we can't seem to create the relationships between the table-based-entities and the view-based-entities. No relationship can exist in the database between a view and a table, as far as I know, so the edmx diagram can't infer it. And I cannot seem to create the relationship manually without getting errors. It thinks all columns in the view are keys.
If I leave it that way I get an error like this for each column in the view:
Association End key property [...] is
not mapped.
If I try to change the "Entity Key" property to false on the columns that are not the key I get this error:
All the key properties of the
EntitySet [...] must be mapped to all
the key properties [...] of table
viewName.
According to this forum post it sounds like a limitation of the Entity Framework.
Update #2
I should also mention the main limitation of the Entity Framework is that it only supports one database at a time. So we need the old data to appear to be in the new database for the Entity Framework to see it. We only need read access of the old system data in the new system.
You can use linked server queries to leave the data where it is, but connect to it from the other db.
Depending on how up-to-date the data in each db needs to be & if one data source can remain read-only you can:
Use the Database Copy Wizard to create an SSIS package
that you can run periodically as a SQL Agent Task
Use snapshot replication
Create a custom BCP in/out process
to get the data to the other db
Use transactional replication, which
can be near-realtime.
If data needs to be read-write in both database then you can use:
transactional replication with
update subscriptions
merge replication
As you go down the list the amount of work involved in maintaining the solution increases. Using linked server queries will work best if its the right fit for what you're trying to achieve.
EDIT: If they're the same server then as suggested by another user you should be able to access the table with servername.databasename.schema.tablename Looks like it's an entity-framework issues & not a db issue.
I don't know about EntityToSql but I know in LinqToSql you can connect to multiple databases/servers in one .dbml if you prefix the tables with:
ServerName.DatabaseName.SchemaName.TableName
MyServer.MyOldDatabase.dbo.Customers
I have been able to click on a table in the .dbml and copy and paste it into the .dbml of the alternate project prefix the name and set up the relationships and it works... like I said this was in LinqToSql, though have not tried it with EntityToSql. I would give it shot before you go though all the work of replication and such.
If Linq-to-Entities cannot cross DB's then Replication or something that emulates it is the only thing that will work.
For performance purposes you probably want either Merge replication or Transactional with queued (not immediate) updating.
Thanks for the responses. We're going to try adding triggers to the old database tables to insert/update/delete records in the new tables of the new database. This way we can continue to use Entity Framework and also do any data transformations we need.
Once the UI functions move over to the new system for a particular feature, we'll remove the table from the old database and add a view to the old database with the same name that points to the new database table for backwards compatibility.
One thing that I realized needs to happen before we can do this is we have to search all our code and sql for ##Identity and replace it with scope_identity() so the triggers don't mess up the Ids in the old system.
I have a couple of questions.
1) Why cannot we see system tables (like sysobjects) under Master/Model/MSBD etc.? But we
can query. Are we basically querying the views, because as they are the main tables that
holds a value able informations?
Like "SELECT * FROM sysobjects". are we basically querying some views?
2) Why cannot we add triggers to system tables?
Thanks in advance
SQL Server 2008 system tables (http://msdn.microsoft.com/en-us/library/ms179932.aspx) have been implemented as read-only views. One cannot directly work with the data in these system tables. You can access SQL Server metadata using catalog views. Do check this link http://msdn.microsoft.com/en-us/library/ms174365.aspx
It is possible to create triggers on system tables but it is generally not recommended. Please check this http://www.sql-server-performance.com/faq/trigger_system_table_p1.aspx
cheers
Since SQL 2005 the catalog views are implemented as views declared in the Resource Database (mssqlsystemresource). Due to some special magic they appear to exist in every database.
You can always use the execution plan to see from what actual tables do these views fetch data from. The underlying tables can be accessed when you are connected with a DAC connection. Modifying the system tables in any way will mark the database and an message will be logged every time the database starts up. Modified databases are not supported by MS, so if something goes wrong you cannot ask for support.