> I have a concern, because this turns automatic checkpointing into a mortal danger for all snapshots.
This sentence may be false. Automatic snapshots are PASSIVE, and I'm not sure passive checkpoints invalidate snapshots returned by sqlite3_snapshot_get(). But i'm not sure, and I would appreciate a confirmation! Thanks is advance, Gwendal Roué On Thu, Sep 26, 2019 at 6:13 PM Gwendal Roué <gwendal.r...@gmail.com> wrote: > Hello, > > The documentation for sqlite3_snapshot_open() [1] says: > > > A call to sqlite3_snapshot_open() will fail to open if the specified > snapshot has been overwritten by a checkpoint. > > And indeed I am able to create a snapshot with sqlite3_snapshot_get() [2], > then run checkpoints with sqlite3_wal_checkpoint_v2() [3], and finally have > sqlite3_snapshot_open() fail. > > I have a concern, because this turns automatic checkpointing into a mortal > danger for all snapshots. As soon as a checkpoint is performed, snapshots > are invalidated, and whoever is relying on them has lost the database state > he's interested into. > > My question is: is it possible to prevent checkpoints from completing > successfully when a snapshot is alive? > > I know this is possible with a "hand-made checkpoint", made of a distinct > connection which has started a deferred transaction and has performed an > initial read. Such hand-made checkpoint has SQLITE_CHECKPOINT_RESTART and > SQLITE_CHECKPOINT_TRUNCATE fail, and are still able to access their > precious database state after a SQLITE_CHECKPOINT_PASSIVE or a > SQLITE_CHECKPOINT_FULL. > > The behavior of those "hand-made checkpoint" matches well the needs of > users who want to use WAL without thinking too much about it: they do not > disable automatic checkpointing, and are guaranteed with a stable access to > a given database state as long as they need it. > > I was wondering if such a behavior is possible with snapshots returned > from sqlite3_snapshot_get(). > > If it is not, then I humbly suggest that this feature would be added, and > am willing to listen to the opinion of SQLite experts on this subject. > > Regards, > Gwendal Roué > > [1] https://www.sqlite.org/c3ref/snapshot_open.html > [2] https://www.sqlite.org/c3ref/snapshot_get.html > [3] https://www.sqlite.org/c3ref/wal_checkpoint_v2.html > > _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
