The helper isn't used yet. The goal is to export this on /camera/<uuid>/ as
described in a TODO in design/api.md.
The next step is to keep MoonfireDatabase::CameraData::days up-to-date:
* Init: call on every recording (replacing the current aggregated query with
a recording-by-recording query)
* InsertRecording, DeleteRecordings: call for added/removed recordings
then return it from GetCamera and pass it along to the client in
WebInterface::HandleJsonCameraDetail.
In particular, this returns all the extra configuration data that will be
necessary to actually instantiate streams from the database rather than the
soon-to-be-removed configuration file.
* Schema revisions. The most dramatic is the addition of a covering index on
(camera_id, start_time_90k) that avoids the need to make sparse accesses
into the recording table (where the desired data is intermixed with both
the large blobs and rows from other cameras). A query over a year's data
previously took many seconds (6+ even in a form without the video_index)
and now is roughly 10X faster. Queries for a couple weeks now should be
unnoticeably fast.
Other changes to shrink the rows, such as duration_90k instead of
end_time_90k (more compact varint encoding) and video_sample_entry_id
(typically 1 byte) instead of video_sample_entry_sha1 (20 bytes).
And more CHECK constraints for good measure.
* Caching of expensive computations and logic to keep them up to date.
The top-level web view previously went through the entire recording table,
which was even slower. Now it is served from a small map in RAM.
* Expanded the scope of operations to cover (hopefully) everything needed for
recording into the SQLite database.
* Added tests of MoonfireDatabase. These are basic tests that don't
exercise a lot of error cases, but at least they exist.
The main MoonfireDatabase functionality still missing is support for quickly
seeing what calendar days have data over the full timespan of a camera. This
is more data to compute and cache.
