mysql - Storing image files in Mongo database, is it a good idea?

Question

When working with mysql, it is a bad idea to store images as BLOB in the database, as it makes the database quite large which is harmful for normal usage of the database. Then, it is better to save image files on disk and save link to them within the database.

However, I think this is different for MongoDB, as increasing the database file size has a negligible influence on performance (this is the reason that MongoDB can successfully handle billions of records).

Do you think it is better to save image files on MongoDB (as GridFS) to reduce number of files stored on the server; or still it is better to keep the database as small as possible?

Answer 1

The problem isn't so much that the database gets big, databases can handle that (although MongoDB isn't as good as many other in that respect). The problem is that to send the data to the client it first has to be moved into RAM by the database, then copied over to the application's memory, then handed off to the kernel to be sent through the socket. It's wasting lots of RAM and CPU cycles. The reason it's better to have large files in the filesystem is that it's easier to get around copying it, you can ask the kernel to stream the file from disk to the socket directly.

The downside of storing large files in the filesystem is that it's much harder to distribute. Using a database, and something like Mongo's GridFS makes it possible to scale out. You just have to make sure you don't copy the whole file into the application's memory at once, but a chunk at a time. Most web app frameworks have some support for sending chunked HTTP responses nowadays.