CODEWITHSUNDEEP
google-app-engine
Shaun Budhram
Shaun Budhram

Reputation: 3710

Performance considerations with db.BlobProperty()

In my app, I'd like to have an entity defined like this:

class MyModel(db.Model):
    title           = db.StringProperty()
    myBlob          = db.BlobProperty()

Say this blob holds around 1 megabyte. Will this slow down any queries I make on the MyModel type? Is it fetching the entire 1mb per entity, or just references until I actually try to access the blob?

Upvotes: 1

Views: 89

Answers (1)

Tim Hoffman
Tim Hoffman

Reputation: 12986

The minute you retrieve the entity, the blob is loaded from the datastore unless you do a projection query.

You have a few options to avoid loading the BlobProperty until you need it.

  1. do a projection query and then only fetch the full entity when you need it.

  2. stick the BlobProperty in a Child entity (make the top level one the ancestor) and only fetch the property with a get, when you need it.

  3. Don't use a BlobProperty but stick it in GCS (Google CLoud Storage) and serve it from there.

The last has the benefit that if you do no processing on the blob your appengine instance doesn't need to get involved with serving it (depending on what your requirements are of course)

Upvotes: 1

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