SQLite's busy timeout defaults to zero, and nothing ever set one: the
loser of a write race got SQLITE_BUSY at the moment it asked. WAL does
not cover this — it makes one writer and many readers free, and this
application constantly has two writers, the face sweep committing a
batch while the derived sync imports shards or reclustering reads.
The cost was not a retry but lost work. A sweep that had already paid
for the detection and the embedding — seconds per image, the expensive
part — discarded the result on "storing faces for 214: database is
locked" and moved on to the next image. Both the desktop and the tablet
logged runs of those on consecutive images, which is a face sweep
quietly failing to store the faces it had just computed.
Ten seconds, on every connection, set in configure() so that nothing
can open the catalog without it — the figure the job runner's own tests
have used for this reason since they were written. It is far longer
than any transaction here, so it bounds pathology rather than making
anyone wait.
dtourolle
9b627e7713