Question

We have a text processing application developed in C# using .NET FW 4.0 where the Administrator can define various settings. All this ‘settings’ data reside in about 50 tables with foreign key relations and Identity primary keys (this one will make it tricky, I think). The entire database is no more than 100K records, with the average table having about 6 short columns. The system is based on MS SQL 2008 R2 Express database.

We face a requirement to create a snapshot of all this data so that the administrator of the system could roll back to one of the snapshots anytime he screws up something. We need to keep the last 5 snapshots only. Creation of the snapshot must be commenced from the application GUI and so must be the rollback to any of the snapshots if needed (use SSMS will not be allowed as direct access to the DB is denied). The system is still in development (are we ever really finished?) which means that new tables and columns are added many times. Thus we need a robust method that can take care of changes automatically (digging code after inserting/changing columns is something we want to avoid unless there’s no other way). The best way would be to tell that “I want to create a snapshot of all tables where the name begins with ‘Admin'”. Obviously, this is quite a DB-intensive task, but due to the fact that it will be used in emergency situations only, this is something that I do not mind. I also do not mind if table locks happen as nothing will try to use these tables while the creation or rollback of the snapshot is in progress.

The problem can be divided into 2 parts:

1. creating the snapshot
2. rolling back to the snapshot

Regarding problem #1. we may have two options:

1. export the data into XML (file or database column)
2. duplicate the data inside SQL into the same or different tables (like creating the same table structure again with the same names as the original tables prefixed with “Backup”).

Regarding problem #2. the biggest issue I see is how to re-import all data into foreign key related tables which use IDENTITY columns for PK generation. I need to delete all data from all affected tables then re-import everything while temporarily relaxing FK constraints and switching off Identity generation. Once data is loaded I should check if FK constraints are still OK.

Or perhaps I should find a logical way to load tables so that constraint checking can remain in place while loading (as we do not have an unmanageable number of tables this could be a viable solution). Of course I need to do all deletion and re-loading in a single transaction, for obvious reasons.

I suspect there may be no pure SQL-based solution for this, although SQL CLR might be of help to avoid moving data out of SQL Server.

Is there anyone out there with the same problem we face? Maybe someone who successfully solved such problem?

I do not expect a step by step instruction. Any help on where to start, which routes to take (export to RAW XML or keep snapshot inside the DB or both), pros/cons would be really helpful.

Thank you for your help and your time.

Daniel

Answer 1

A kind of versioning by date ranges is a common method for records in Enterprise applications. As an example we have a table for business entities (us) or companies (uk) and we keep the current official name in another table as follows:

CompanyID    Name            ValidFrom     ValidTo
12           Business Lld    2000-01-01    2008-09-23
12           Business Inc    2008-09-23    NULL

The null in the last record means that this is current one. You may use the above logic and possibly add more columns to gain more control. This way there are no duplicates, you can keep the history up to any level and synchronize the current values across tables easily. Finally the performance will be great.