> Le 15 févr. 2017 à 16:04, Olivier Mascia <o...@integral.be> a écrit : > > Dear all, > > https://www.sqlite.org/c3ref/backup_finish.html#sqlite3backupstep makes it > clear that connections (other than the one used for the backup feature) which > writes in between calls to sqlite3_backup_step() will force the next > sqlite3_backup_step() to start again the whole copy processing. > > What about databases set for journal_mode=WAL? > Is backup_step() also restarting the whole procedure after any write commit > happen? > Or only if some checkpointing occurs? > > Said differently, is the whole scheme of sqlite3_backup_* API meant to build > a copy of the database, including whatever would be in the WAL journal, or is > the goal to get a copy of what is seen by the implicit read transaction of > the connection doing the backup?
Answering my own post, now that I have prepared and experimented with a test program: backup_step() indeed restarts its work for *any* write occurring during the backup, even though the test db is set for journal_mode=WAL and no checkpointing occurs (verified) at the end of the commit of any of those test writes. Has anyone ever wanted the sqlite3_backup_* API to be able to proceed differently, when journal_mode=WAL? Something along the lines of starting a transaction (deferred) on _init, _step() copying the database as seen by this transaction, and _finish() releasing that read-transaction? It wouldn’t copy changes occurring after the backup/copy has started, of course, but would copy a complete stable snapshot of the database, without impacting (excepting the backup I/O) neither the readers or being cancelled/restarted by the occasional writer? Passive checkpointing as done by default by Sqlite3 wouldn’t even impact the process. I for sure have a nice use case for this. :) -- Best Regards, Meilleures salutations, Met vriendelijke groeten, Olivier Mascia, http://integral.software _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
