Question

I am hoping someone can explain how to use BLOBs. I see that BLOBs can be used to store video files. My question is why would a person store a video file in a BLOB in a SQL database? What are the advantages and disadvantages compared to storing pointers to the location of the video file?

Answer 1

A few different reasons.

If you store a pointer to a file on disk (presumably using the BFILE data type), you have to ensure that your database is updated whenever files are moved, renamed, or deleted on disk. It’s relatively common when you store data like this that over time your database gets out of sync with the file system and you end up with broken links and orphaned content.

If you store a pointer to a file on disk, you cannot use transactional semantics when you’re dealing with multimedia. Since you can’t do something like issue a rollback against a file system, you either have to deal with the fact that you’re going to have situations where the data on the file system doesn’t match the data in the database (i.e. someone uploaded a video to the file system but the transaction that created the author and title in the database failed or vice versa) or you have to add additional steps to the file upload to simulate transactional semantics (i.e. upload a second <>_done.txt file that just contains the number of bytes in the actual file that was uploaded. That’s cumbersome and error-prone and may create usability issues.

For many applications, having the database serve up data is the easiest way to provide it to a user. If you want to avoid giving a user a direct FTP URL to your files because they could use that to bypass some application-level security, the easiest option is to have a database-backed application where to retrieve the data, the database reads it from the file system and then returns it to the middle tier which then sends the data to the client. If you’re going to have to read the data into the database every time the data is retrieved, it often makes more sense to just store the data directly in the database and to let the database read it from its data files when the user asks for it.

Finally, databases like Oracle provide additional utilities for working with multimedia data in the database. Oracle interMedia, for example, provides a rich set of objects to interact with video data stored in the database– you can easily tag where scenes begin or end, tag where various subjects are discussed, when the video was recorded, who recorded it, etc. And you can integrate that search functionality with searches against all your relational data. Of course, you could write an application on top of the database that did all those things as well but then you’re either writing a lot of code or using another framework in your app. It’s often much easier to leverage the database functionality.