The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 1: Storing and Managing Unstructured DataConversely, if an application needs to store a PDF version of every quote sent to acustomer, then there is tighter coupling and it may make more sense to store the LOBs inthe database.Regardless of the route that seems most appropriate for your application, there are advantagesand disadvantages to each approach, based on considerations of:• transactional consistency• data manageability and recoverability• security• performance.We'll briefly discuss these issues in the coming sections, and further details can befound in Paul Randal's white paper, FILESTREAM Storage in SQL Server 2008(http://brurl.com/fs1).Transactional consistencyOne of the fundamental advantages of storing data in a relational database is that, viathe implementation of various transaction isolation levels, locking mechanisms, and soon, the relational engine guarantees a transactionally-consistent view of the data, at anypoint in time. In other words, it guarantees that transactions within SQL Server conformto the ACID properties, and so prevents interference between transactions on the samedata, and ensures that transactional operations can succeed or fail together, as a batch.By storing LOBs within the database, we can ensure that this transactional consistencyextends to the LOB data as well as other relational data within the database. For example,assume that a user uploads a document (a BLOB) into a document management applicationthat uses SQL Server storage. The operation involves inserting a new row into atable along with the relational data (such as the document name) and the BLOB data (the33