Please add this explanation to the wiki. I'd do it, but i'm working with an RDBMS right now and I am neither distributed nor eventually consistent. --- Jeremiah Peschka - Founder, Brent Ozar PLF, LLC Microsoft SQL Server MVP
On Nov 2, 2011, at 8:18 AM, Ryan Zezeski wrote: > On Tue, Nov 1, 2011 at 5:51 PM, Justin Karneges <jus...@affinix.com> wrote: > Are you saying that allow_mult=false + last_write_win=false is the same as > allow_mult=false + last_write_win=true ? > > False/false may be the default behavior, but I want to know what that behavior > is. :) > > > Justin, > > No, last_write_wins=true doesn't care about the value of allow_mult. Only > one should be true at the same time, and the default is to have both set to > false. Perhaps making an imaginary setting to displace these two would help. > Lets call this imaginary setting "conflict_resolution_method" which can take > on the three mutually exclusive values "stomp", "most_recent" and "siblings". > > stomp - overwrite the current value with the new value regardless of vector > clocks, just mutate the value with no regard, thus "stomp" > > most_recent - use vclocks to monitor for conflicts, create siblings, and pick > the most recent write when a conflict does occur (i.e. let Riak handle the > conflict for you based on time) > > siblings - use vclocks to monitor for conflicts, create siblings, and return > the siblings to the client when a conflict occurs for it to be resolved by > some application dependent logic > > Now lets map my imaginary field to the actual fields > > stomp = last_write_wins=true + allow_mult=false > > most_recent = last_write_wins=false + allow_mult=false > > siblings = last_write_wins=false + allow_mult=true > > Notice that setting both to true has undefined semantics as they are > necessarily mutually exclusive. > > Also notice that stomp and most_recent might seem like the same thing on the > surface but they may have different outcomes in different situations. For > example, stomp would prove to be non-deterministic during the healing of a > split-brain because it will depend on the order of the hinted handoff > transfers. Honestly, you're best avoiding last_write_wins at this point > because it can cause non-obvious behavior and there is potential it may be > removed in the future. > > HTH, > -Ryan > > _______________________________________________ > riak-users mailing list > riak-users@lists.basho.com > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com _______________________________________________ riak-users mailing list riak-users@lists.basho.com http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
