An Object Storage read is slower than a disk of database access.
It might take ~200 to 300ms to retrieve a file content.
This is not an issue for attachments such as the pdf files or any
attachment that we want to read on demand. But that's too slow for
files needed to render a web page.
We'll store in the database:
* Assets (js, css, ...). As a side effect, the databases will be more
portable, as assets are rebuilt frequently, storing them in the Object
Storage led the integration server to try to read assets deleted since
long ago
* Attachments linked to Binary fields named 'image_small',
'image_medium', 'web_icon_data'. Those fields are often used on kanban
views that display a lot a images and retrieving them all was then
very slow (Odoo does not do async requests).
The migration to S3 is no longer called during initialization of the
registry: it would be too slow as we would have to define if the
attachments must be kept in database or sent to S3 on each new start. It
means we have to call `env['ir.attachment'].force_storage()` to run the
migration.
* store the S3 uri in the 'store_fname' (s3://bucket/key)
* the read-only mode is now built-in, as we store the bucket name, if a
instance is started with a different bucket or another filestore
method, it will continue to read the previous attachments on their
stored bucket, but new attachments will be stored on the new one
* remove config in ir.config_parameter, it makes all the stuff more
complex and we don't use them (config file would be more interesting)
* automatically migrate the attachments on loading of the server, so
if an ir.attachment has been created during the module
upgrade/initialization before attachment_s3 is loaded, it will be sent
to S3 as soon as it's loaded
Guewen Baconnier