The commitlog defaults to periodic mode, which writes a sync marker to the file and fsync's the data to disk every 10s by default.
`nodetool flush` will force a sync marker / fsync Data written since the last fsync will not be replayed on startup and will be lost. If you drop the periodic time, the number of writes you lose on restart decreases. Alternatively, you can switch to group/batch commitlog, and it goes to zero, but you'll fsync far more frequently. On Tue, Nov 10, 2020 at 4:19 PM Florin Andrei <flo...@andrei.myip.org> wrote: > That sounds great! Now here's my question: > > I do "nodetool flush", then snapshot the storage. Meanwhile, the DB is > under heavy read/write traffic, with lots of writes per second. What's > the worst that could happen, lose a few writes? > > > On 2020-11-10 15:59, Jeff Jirsa wrote: > > If you want all of the instances to be consistent with each other, > > this is much harder, but if you only want a container that can stop > > and resume, you don't have to do anything more than flush + snapshot > > the storage. The data files on cassandra should ALWAYS be in a state > > where the database will restart, because they have to be to tolerate > > power outage. > > > > On Tue, Nov 10, 2020 at 3:39 PM Florin Andrei <flo...@andrei.myip.org> > > wrote: > > > >> Running Apache Cassandra 3 in Docker. I need to snapshot the storage > >> > >> volumes. Obviously, I want to be able to re-launch Cassandra from > >> the > >> snapshots later on. So the snapshots need to be in a consistent > >> state. > >> > >> With most DBs, the sequence of events is this: > >> > >> - flush the DB to disk > >> - "freeze" the DB > >> - snapshot the storage > >> - "unfreeze" the DB > >> > >> What does that sequence translate to, in Cassandra parlance? > >> > >> What is the sequence of events that needs to happen when I bring the > >> DB > >> up from an old snapshot? Will there be a restore procedure, or can I > >> > >> just start it as usual? > >> > >> -- > >> Florin Andrei > >> https://florin.myip.org/ > >> > >> > > --------------------------------------------------------------------- > >> To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org > >> For additional commands, e-mail: user-h...@cassandra.apache.org > > -- > Florin Andrei > https://florin.myip.org/ > > --------------------------------------------------------------------- > To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org > For additional commands, e-mail: user-h...@cassandra.apache.org > >
