On Fri, 2010-12-10 at 15:13 +0000, Philip Martin wrote: > Julian Foad <julian.f...@wandisco.com> writes: > > > Until recently I have been thinking the best way is to code the "remove > > this one" call into the appropriate place in each libsvn_wc code path, > > but I'm changing my mind. That's feasible in some places but I think > > it's too difficult in general, because some of the places where we lose > > a reference are down within some WC-DB-layer function that may delete or > > overwrite several rows as part of its operation. > > > > Instead, I think we should be using some kind of reference-counting or > > reference-tracking in the WC-DB layer. It could use the 'refcount' > > column that already exists in the 'pristine' table. It could use a > > separate list of "pristines that may have become unreferenced" which > > could accumulate in the DB during the course of a high-level operation > > and could then be scanned at the end of the op, perhaps after processing > > the Work Queue. > > If a code path makes it difficult to remove individual pristines how > will it be possible to update the reference count?
What I mean is that rather than calling svn_wc__db_pristine_remove() from various (higher level) places in general libsvn_wc code, we can instead keep it entirely within wc_db.c and decrement the ref count whenever any wc_db function removes or overwrites a reference. Those places are easier to find. > I wonder if an SQLite trigger could be used. > > > I'll also look into the possibility of working to a constraint that > > every pristine SHA1 reference in the DB should at all times refer to an > > actual entry in the 'pristine' table. At the moment, as I understand > > it, we may sometimes insert the reference before installing the > > referenced text. That's not necessarily wrong but I feel we'd have a > > stringer design if we can re-order the code such that this constraint is s/stringer/stronger/ > > satisfied at all times. I see from the SQLite docs that a 'REFERENCES' > > constraint can be enforced by sqlite >= 3.6.19. > > We alrady use REFERENCES for wc_id and repos_id. Yup. - Julian
