A domain with no new rows kept its last row's stamp, so once that was older than the tombstone horizon every pull answered cursorExpired and the client resynced from scratch on every pull. A domain whose page runs dry now takes serverNow minus the overlap on every page where its watermark has not passed that line, and on the last page every row domain does, raising a quiet domain and holding back one that delivered rows in the stretch. A domain drained early in a long walk is covered as well. The overlap grows from 60 to 120 seconds, above the 60-second timeout of the longest transactions that write served rows.
A page's watermark is its last row's stamp, and a long import stamps its rows before it commits them: a quick write committing in between carried the watermark past them, and the keyset never returned them. A caught-up page now hands out watermarks at most a minute before serverNow in every row domain, as start=now does, so the next pull reads that minute again. The mirror domain keeps its watermark.
updatedAt is stamped when a write is built, not when it commits, so a
transaction in flight when the cursor was handed out could commit a row
stamped before it, and a watermark at serverNow skipped that row for
good. The watermarks now sit one minute back; client upserts are
idempotent, so the overlap is harmless. The token's issue time stays
serverNow.
GET /api/sync/changes?start=now answers an empty page whose cursor sits at
serverNow in every domain, in the same opaque format the feed hands out.
A client that only needs what changes from now on, such as the Apple
Health write-back, pages forward from it instead of draining the whole
history first. start and cursor together are refused with 422.
Refs #1339
Marc-André Bombeck