The workflow storage migration rewrites old-form image rows (text inline)
to document ids, batch by batch:
- Each batch is one BEGIN IMMEDIATE transaction of at most 200 rows or
16 MB of text, found by a rowid range search and read one row at a time.
- Each text is stored or reused, then read back through the one accessor
before its row changes; a text that would not come back identical fails
and rolls back the whole batch.
- A value that is not text stays inline and is counted as protected.
- A crash or a stop leaves committed batches new form and the rest old
form; both read the same, and a rerun continues. No media file is opened.
- Unreferenced documents are swept at the end.
The maintenance preview gains a read-only workflow_storage plan (records to
rewrite, inline bytes where SQLite has octet_length, the Reclaim space and
older-version notes). reclaim_space sweeps, runs VACUUM and truncates the
WAL so the freed pages go back to the disk.
Vito Sansevero
02b0e6813f