.NET Audit Log Design

I am looking for advice on a high level design approach to build an audit trail for a financial application.  Need to track every change made to every financial record.  Our development team has spent much time and effort using SQL triggers to detect record-level changes.  This turned out to be a major disaster as it caused significant performance problems.  How are audit mechanisms effectively implemented in large .NET applications?  Thanks in advance!
dev775Asked:
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Vitor MontalvãoMSSQL Senior EngineerCommented:
Which SQL Server version are you working with?
What you want to audit/track? i.e., do you want to record the columns changed and keep track to the previous value and the  new value or you just want to record who changed the data (no matter which) and when?
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dev775Author Commented:
Our software currently supports SQL 2008 or 2012.  What do we want to keep track of... a) any change to a data field; b) when a record was accessed (even if only to view); c) date/time of change; d) who made the change; & d) from what workstation the change was made.  We need to have a sequential record of changes and yes, we need a history of the actual values that were changed.  For example if a customer phone number is changed we would want to record previous value and new value.
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Vitor MontalvãoMSSQL Senior EngineerCommented:
Ok, then I will suggest you to get into SQL Server Audit starting by reading this good article in MSDN.
You can create an audit and set it to write in a log file and what you want to audit may be performed by this command example:
CREATE DATABASE AUDIT SPECIFICATION PCI_Txn_Database_Spec
FOR SERVER AUDIT PCI_Audit
  ADD (DATABASE_OBJECT_PERMISSION_CHANGE_GROUP),
  ADD (SELECT ON dbo.Customer BY dbo),
  ADD (INSERT ON dbo.Customer BY dbo),
  ADD (UPDATE ON dbo.Customer BY dbo),
  ADD (DELETE ON dbo.Customer BY dbo),
  ADD (EXECUTE ON dbo.usp_SubmitPO BY public)

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melmersCommented:
Hello,

i would think when you use the Event Sourcing pattern for your application it could,
be archiveid what you want. as Reference you could read http://msdn.microsoft.com/en-us/library/dn589792.aspx or http://martinfowler.com/eaaDev/EventSourcing.html 

But it comes to the cost that your application has an higher performance request and you need
to design this explicit and can't use ORM Mapper out of the box.

When you have an application with this pattern you can audit or rollback to any state of change
if you only use this pattern for database access. If you use other strategies like ORM or direct SQL for
some task then your data can be corrupted and not rollback complete because the event store has not
record all changes.
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dev775Author Commented:
Thanks for the helpful comments.  Regarding the SQL Server Audit, what is the likely cost on performance from the standpoint of the client application user?  Will it be possible to store the audit data in another SQL DB?
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Walter PadrónCommented:
Auditing is a common example of a CROSS-CUTTING CONCERN. Because of the SRP principle, i suggest that you didn't implement it at the dataaccess layer/database level and instead at the aplication domain.

Using a DECORATOR pattern you can easily add such behaviour to your project
http://en.wikipedia.org/wiki/Decorator_pattern

Best regards

PD: I forget to add that this design makes your system very TESTABLE
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Vitor MontalvãoMSSQL Senior EngineerCommented:
In the article I sent in my previous post you can see a table comparing the performance impact with the use of trace. Auditing will always has impact no matter the solution you chose but my recommendation is to use the native SQL Server Audit since has better performance than traces and so will impact less.
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Scott PletcherSenior DBACommented:
The only way to do what you want outside of 3rd party products is SQL Server Audit.

Be aware, though, that this is not an easy thing to learn and implement.  You'll need plenty of time for defining, testing and verifying the audit setup, and verifying that all accesses are being logged as expected.

Also, once Audit is in place on for an instance, it's a prerequisite for that instance: if there's an Audit error during SQL start up, the instance can't start up at all.
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dev775Author Commented:
Thank you for your help!  --Rob
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