I believe the inotifywait does not actually wait for the fsync operation before notifying.
Process A can write to a file, the OS can cache it without flushing to disk, and a request by process B will be served directly from the cache. Therefore the operating system can notify you of the change before it's written to persistent storage. So, in normal synchronous mode, SQLite doesn't cache its writes, it just waits before calling fsync and relies on the OS cache. Perhaps benchmarking before engaging in such an endeavour as you plan would indicate whether the OS cache gives you sufficient performance. > On 29 Dec 2017, at 12:07 pm, Ian Freeman <i...@ifreeman.net> wrote: > > Thanks, Simon. Indeed I did see that option. But I'm concerned about > maintaining integrity in the middle of an power-interrupted commit, so > I was hoping to leverage WAL's inverted behavior of not modifying the > database file directly until checkpoint time. The only thing left to > investigate is how WAL handles power loss during the middle of a > checkpoint. Normally I believe it's able to recover because the next db > open has the -wal file to look at. But not if I'm storing it in-memory. > > So I'm thinking I will copy the -wal file to disk before the checkpoint > op for safety, and then load it back onto ramdisk after. I suppose I > may have to exit WAL mode in order to perform that copy, making > checkpointing a very expensive operation for my app. > >>> On Fri, 2017-12-29 at 16:48 +0000, Simon Slavin wrote: >>> >>> On 29 Dec 2017, at 4:34pm, Ian Freeman <i...@ifreeman.net> wrote: >>> >>> I see, then what I'm seeing is just normal behavior of the writes >>> being >>> flushed to disk. I read what I wanted to hear about >>> synchronous=NORMAL >>> delaying writes to the -wal file. Instead I'm going to see if I can >>> move -wal to a ramdisk and see how that will affect db integrity >>> with >>> power losses at in-opportune times. >> >> Did you see >> >> PRAGMA journal_mode = MEMORY >> >> ? >> >> Simon. >> _______________________________________________ >> sqlite-users mailing list >> sqlite-users@mailinglists.sqlite.org >> http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ > sqlite-users mailing list > sqlite-users@mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
