Key rotation re-sealed a single-value backup in place, which holds the
stored string, its bytes, the plaintext and the new ciphertext at once; a
copy can be over a hundred megabytes and the in-app rotation walked 25 of
them per page, enough to run a 1 GB container out of memory. Rotation now
converts each such copy into pieces under the active key instead, one row
at a time. The ~hlgcm1. stream of v1.38.6 to v1.39.1 is read a megabyte
at a time with its tag checked at the end, inside one transaction, so a
copy that fails the check is left untouched; the copy keeps its date. The
scan reads only the first characters of each value. Measured on a copy of
a 2.6 million-reading account (126 MB stored): converted in 25 s with the
heap flat at 57 MB under a 200 MB limit, where re-sealing in place ran out
of heap.
The weekly and manual backup leave an account alone while a restore of
its current copy is queued or running, and count it as skipped, not
failed. A reader whose copy is replaced mid-read answers 409
backup_changed, "replaced by a newer one while it was being read", rather
than the undecryptable error; a restore rolls back with the same code.
Pieces are sealed with a fixed associated-data label, so a value the same
key sealed for another purpose never opens as a piece; rotation re-seals
under the same label. A row holding both a single value and pieces, which
only an older release writing after a downgrade produces, is refused with
a message saying so, and the next weekly run replaces it. Rotation treats a
row deleted between its read and its write as gone rather than an error.
The corpus walk and the rotation script paged with Prisma's cursor and skip.
Prisma resolves that cursor by reading the page's last row again, so when
that row was hard-deleted before the next page (a backup replaced, a cached
response expired), the next page came back empty and the walk ended early.
The scan then counted fewer rows than the database holds, which could read
as nothing left on the old key while rows it never reached still were.
Both walks now ask for the rows whose id is greater than the last one read,
which needs no row to still exist.
Marc-André Bombeck