No it's never safe to set it to 0 as you'll disable hinted handoff for the table. If you are never doing updates and manual deletes and you always insert with a ttl you can get away with setting it to the hinted handoff period.
On 6 Oct. 2017 1:28 am, "eugene miretsky" <eugene.miret...@gmail.com> wrote: > Thanks Jeff, > > Make sense. > If we never use updates (time series data), is it safe to set > gc_grace_seconds=0. > > > > On Wed, Oct 4, 2017 at 5:59 PM, Jeff Jirsa <jji...@gmail.com> wrote: > >> >> The TTL'd cell is treated as a tombstone. gc_grace_seconds applies to >> TTL'd cells, because even though the data is TTL'd, it may have been >> written on top of another live cell that wasn't ttl'd: >> >> Imagine a test table, simple key->value (k, v). >> >> INSERT INTO table(k,v) values(1,1); >> Kill 1 of the 3 nodes >> UPDATE table USING TTL 60 SET v=1 WHERE k=1 ; >> 60 seconds later, the live nodes will see that data as deleted, but when >> that dead node comes back to life, it needs to learn of the deletion. >> >> >> >> On Wed, Oct 4, 2017 at 2:05 PM, eugene miretsky < >> eugene.miret...@gmail.com> wrote: >> >>> Hello, >>> >>> The following link says that TTLs generate tombstones - >>> https://docs.datastax.com/en/cql/3.3/cql/cql_using/useExpire.html. >>> >>> What exactly is the process that converts the TTL into a tombstone? >>> >>> 1. Is an actual new tombstone cell created when the TTL expires? >>> 2. Or, is the TTLed cell treated as a tombstone? >>> >>> >>> Also, does gc_grace_period have an effect on TTLed cells? >>> gc_grace_period is meant to protect from deleted data re-appearing if the >>> tombstone is compacted away before all nodes have reached a consistent >>> state. However, since the ttl is stored in the cell (in liveness_info), >>> there is no way for the cell to re-appear (the ttl will still be there) >>> >>> Cheers, >>> Eugene >>> >>> >> >
