Heikki Linnakangas wrote: >> Gregory Stark wrote: >> However you still have a problem that someone could come along and set the >> hint bit between calculating the CRC and actually calling write. > > The double-buffering will solve that.
Or simply require that hint bit writes acquire a write lock on the page (which should be available if not being critically updated or flushed); thereby to write/flush, simply do the same, calc it's crc, write/flush to disk, then release it's lock; and which seems like the most reliable thing to do (although no expert on pg's implementation by any means). As I would guess although there may be occasional lock contention, its likely minor, and greatly simplify the whole process it would seem? (unless I misunderstand, even double buffering requires a lock, as if multiple hint bits may be updated during the copy, the resulting copy may be inconsistent if only partially reflecting the updates in progress) -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
