Can I implement symmetricDS in identical databases?
My scenerio
I have to databases:
Database A
Database B
Whatever data change happens in either one of them should reflect in the other:
Current situation:
Even though the DB are identical, database B have less tables that database A
Consider a table tableA from database A and same table in database B
But pk id for same records are actually different in two tables
Can i expand and implement symmetricDS if i want to expand to a third database
Currently i am using a mapping table and API to handle datasync.
Can i move to symmetricDS for syncing data
Yes, go ahead
SymemtricDs allows for bidirectional synchronization of databases
Only the tables of database B will be configured for synchronization. The extra tables from database A might be added to the mix using table transformation.
As long as there are constraints of uniqueness on columns in, for example, database A that are PKs in database B that will not be a problem.
You can add as many types and instances of those types of databases. Bear in mind that the graph of database relationships must satisfy the definition of a tree.
Related
How do I store data that is shared between databases?
Suppose a database for a contact management system. Each user is given a separate database. User can store his/her contacts' education information.
Currently there's a table called School in every database where the name of every school in the country is stored. School table is referenced as a FK by Contact table.
School table gets updated every year or so, as new schools get added or existing schools change names.
As the school information is common across all user databases, moving it into a separate common database seems to be a better idea. but when it's moved to a separate database, you can not create a FK constraint between School and Contact.
What is the best practice for this kind of situation?
(p.s. I'm using SQL Server if that is relevant)
Things to consider
Database is a unit of backup/restore.
It may not be possible to restore two databases to the same point in time.
Foreign keys are not supported across databases.
Hence, I would suggest managing the School -- and any other common table -- in one reference DB and then replicating those tables to other DBs.
Just straight out of the box, foreign key constraints aren't going to help you. You could look into replicating the individual schools table.
Based on the fact that you won't query tables with the SchoolID column very often I'll asume that inserts/updates to these tables will be really rare... In this case you could create a constraint on the table in which you need the FKs that checks for the existence of such SchoolID in the Schools table.
Note that every insert/update to the table with the SchoolID column will literally perform a query to another DB so, distance between databases, the way they connect to each other and many other factors may impact the performance of the insert/update statements.
Still, if they're on the same server and you have your indexes and primary keys all set up, the query should be fairly fast.
Situation
I have 5 Access DB files, each one has 10 tables, 40 queries and 8 macros. All 5 Access DB files have same table name, table structure, same queries and same macros. The only different is the data contain in the table. If it matters, some tables on each database has rows between few hundreds to 100K+.
What I am trying to achieve
I am migrating these 5 Access DB files to single SQL Server (2008) database. Edit: After migrating, I do need to know which tables belong to which database since each original Access DB is associated with company's department so I need to keep track of this.
My Solutions or Options
Tables will be imported to SQL Server as tables. Queries will be imported as Stored Procedures. Macro will be imported as new Stored Procedures.
Import each Access DB's tables and queries to SQL Server DB and rename each tables and queries by giving them prefix to identify which tables belong to which database.
Same as #1, however, only import tables. As for the queries, only import one set of queries (40 queries) and modify them to dynamically select, insert, update or delete from the tables.
Import table A from 1st Access DB, table A from 2nd Access DB, table A from 3rd Access DB and so on, to one new table in SQL Server and give them unique identifier to identify which row of data belong to which database.
What do you think is the best approach? Please tell me if there is better way to do this than what I have listed. Thanks!
I would migrate them to MS SQL like so:
Import all tables from database 1 into corresponding tables from SQL Server, but add a new primary key with the name of the old one, rename the old pk and identifier for the database.
Update all foreign keys to the new pk field using the old pk and the identifier.
Repeat for databases 2-5
Either delete the identifier or keep it, depending if you need to know where the rows came from (same for old primary keys)
Only import queries/macros once, as they are the same.
When doing it this way, you keep the pk-fk relations and the queries intact and still know where the rows came from.
I would say number 3. You would get no duplication code and much easier maintenance.
One example of easier maintenance is performance tuning. You say the queries are the same in the 5 access DBs: say you detect one of the queries runs too slow and you decide that you need to create an index on an underlying table. In option #1 and #2 this would mean recreating the same index on 5 "twin" tables.
In access for each of these databases, you could assign each of the department field id (new field) with it's on identifier in a new table (each department has different value), and then add this value to each of the tables that is to be imported. Create a new table that has the department information in it, then create join table that connect these tables. Thus, each department is differentiated between each other.
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?
I was thinking of putting staging tables and stored procedures that update those tables into their own schema. Such that when importing data from SomeTable to the datawarehouse, I would run a Initial.StageSomeTable procedure which would insert the data into the Initial.SomeTable table. This way all the procs and tables dealing with the Initial staging are grouped together. Then I'd have a Validation schema for that stage of the ETL, etc.
This seems cleaner than trying to uniquely name all these very similar tables, since each table will have multiple instances of itself throughout the staging process.
Question: Is using a user schema to group tables/procs/views together an appropriate use of user schemas in MS SQL Server? Or are user schemas supposed to be used for security, such as grouping permissions together for objects?
This is actually a recommended practice. Take a look at the Microsoft Business Intelligence ETL Design Practices from the Project Real. You will find (download doc from the first link) that they use quite a few schemata to group and identify objects in the warehouse.
In addition to dbo and etl, they also use admin, audit, part, olap and a few more.
I think it's appropriate enough, it doesn't really matter, you could use another database if you liked which is actually what we do.
I'm not sure why you would want a validation schema though, what are you going to do there?
Both the reasons you list (purpose/intent, security) are valid reasons to use schemas. Once you start using them, you should always specify schema when referencing an object (although I'm lazy and never specify dbo).
One trick we use is to have the same-named table in each of several schemas, combined with table partitioning (available in SQL 2005 and up). Load the data in first schema, then when it's validated "swap" the partition into dbo--after swapping the dbo partition into a "dumpster" schema copy of the table. Net Production downtime is measured in seconds, and it's all carefully wrapped in a declared transaction.
Is it possible to have same table name on different schema with different data on the tables within the one database? I think rather than create multiple database (that hold same table name) i should create multiple schema instead.
Something like:
Schema 1:
table A, table B
Schema 2:
table B, table X
PS: table B hold different data for each schema
And most basic question did every schema (user) hold different table set? In SQL Server and MySQL every user on same database have same table set, the difference was only on roles, how about Oracle?
Thanks
Yes this is possible. A schema in Oracle is what a MySQL user would call a database.
However, you need to be careful when accessing either of the tables now if the user you connect with to the database instance has access to both. To unambiguously reference a table in a specific schema, use schema.table.
Here's the documentation on namespaces: https://docs.oracle.com/en/database/oracle/oracle-database/20/sqlrf/Database-Object-Names-and-Qualifiers.html#GUID-3C59E44A-5140-4BCA-B9E1-3039C8050C49
As jackrabbit says objects in different schemas have different namespaces.
Each schema in the database has its own namespaces for the objects it contains. This means, for example, that two tables in different schemas are in different namespaces and can have the same name.
Within a schema things are a little more complex.
Because tables and views are in the same namespace, a table and a view in the same schema cannot have the same name. However, tables and indexes are in different namespaces. Therefore, a table and an index in the same schema can have the same name.