The media table was originally introduced when Anki hashed media filenames,
and needed a way to remember the original filename. It also helped with:
1) getting a quick list of all media used in the deck, or the media added
since the last sync, for mobile clients
2) merging identical files with different names
But had some drawbacks:
- every operation that modifies templates, models or facts meant generating
the q/a and checking if any new media had appeared
- each entry is about 70 bytes, and some decks have 100k+ media files
So we remove the media table. We address 1) by being more intelligent about
media downloads on the mobile platform. We ask the user after a full sync if
they want to look for missing media, and they can choose not to if they know
they haven't added any. And on a partial sync, we can scan the contents of the
incoming facts for media references, and download any references we find. This
also avoids all the issues people had with media not downloading because it
was in their media folder but not in the media database.
For 2), when copying media to the media folder, if we have a duplicate
filename, we check if that file has the same md5, and avoid copying if so.
This won't merge identical content that has separate names, but instances
where users need that are rare.
The 'entry due' is the due time of a failed card before it enters the learning
queue. When the card graduates or is removed, it has its old due time
restored. We could pull this from the revlog, but it's cheaper to do it this
way.
We originally were triggering on 100 opcodes, because at the time we were
doing write-heavy alterations to the DB for inactive tags, and a higher level
of opcodes would pause the interface for a long time. The query structure is
different now, so we can afford to save the overhead of more frequent calls.
With the change, a .reset() triggers the handler 3 times; fixIntegrity()
triggers it 30 times over a period of 4.5 seconds.
A lot of the old checks in fixIntegrity() are no longer relevant, and some of
the others may no longer be required. They can be added back in as the need
arises.
We want to ensure that we never recycle ids from deleted cards. We could do
this with an autoincrement column in sqlite, but it's cheaper for us to handle
the ids ourselves, as the deck object is always in memory.
