A thumbnail is the one derived artefact worth sending over the wire: it costs
a range fetch plus a decode to produce and is identical for every client
looking at the same file. A second device that downloads a shard gets a full
grid without fetching a byte of RAW.
Sharded at 25 MB, filled sequentially. The cap is about sync granularity, not
SQLite's limits — one growing database means every client re-downloads it
whenever a single thumbnail is added, whereas with sequential fill only the
newest shard is ever dirty and sealed shards are safe to cache forever.
Stored JPEG-encoded rather than as raw RGBA: a 256px RGBA buffer is ~256 KB
against ~20 KB encoded, and that 13x is transfer cost on every client.
Keyed on Nextcloud's oc:fileid, stable across server-side rename and move.
Assisted-by: LLM
dtourolle
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