Donald: Since we are traversing the ring in a clockwise fashion, the data is written into the next partition you would run into moving forward. You can see how the partitions are chosen in chash:ordered_from/2 at https://github.com/basho/riak_core/blob/master/src/chash.erl#L138. The preference list is built using the partitions that come after the hashed value.
If you consider the partition's name to be the end value that the partition holds, the an object that hashes to 1045375627425331784151332358177649483819648417632 being assigned to 1096126227998177188652763624537212264741949407232 makes sense. That partition would hold items that hash from 913438523331814323877303020447676887284957839361 to 1096126227998177188652763624537212264741949407232 Does this help? Thanks, Charlie Voiselle On Jan 24, 2013, at 12:05 AM, Donald Yan <dyan....@gmail.com> wrote: > Hi there, > > I'm reading this page at > http://docs.basho.com/riak/latest/references/appendices/concepts/Replication/#Understanding-replication-by-example > and have a question about the example given in the page. I quote it here: > " > The DocIdx hash is a 160 bit integer: > > (dev1@127.0.0.1)5> <<I:160/integer>> = DocIdx. > <<183,28,67,173,80,128,26,94,190,198,65,15,27,243,135,127,121,101,255,96>> > (dev1@127.0.0.1)6> I. > 1045375627425331784151332358177649483819648417632 > The node looks up the hashed key in the ring which returns a list of > “preferred” partitions for the given key. > > (node1@127.0.0.1)> Preflist = riak_core_ring:preflist(DocIdx, Ring). > [{1096126227998177188652763624537212264741949407232, 'dev1@127.0.0.1'}, > {1278813932664540053428224228626747642198940975104, 'dev2@127.0.0.1'}, > {0, 'dev1@127.0.0.1'}, > {182687704666362864775460604089535377456991567872, 'dev2@127.0.0.1'}, > {365375409332725729550921208179070754913983135744, 'dev3@127.0.0.1'}, > {548063113999088594326381812268606132370974703616, 'dev1@127.0.0.1'}, > {730750818665451459101842416358141509827966271488, 'dev2@127.0.0.1'}, > {913438523331814323877303020447676887284957839360, 'dev3@127.0.0.1'}] > > " > > I question is since the key is calculated as > "1045375627425331784151332358177649483819648417632", shouldn't the prefer > list be like the following instead? > " > [{913438523331814323877303020447676887284957839360, 'dev3@127.0.0.1'}, > {1096126227998177188652763624537212264741949407232, 'dev1@127.0.0.1'}, > {1278813932664540053428224228626747642198940975104, 'dev2@127.0.0.1'}, > {0, 'dev1@127.0.0.1'}, > {182687704666362864775460604089535377456991567872, 'dev2@127.0.0.1'}, > {365375409332725729550921208179070754913983135744, 'dev3@127.0.0.1'}, > {548063113999088594326381812268606132370974703616, 'dev1@127.0.0.1'}, > {730750818665451459101842416358141509827966271488, 'dev2@127.0.0.1'}] > " > because value "1045375627425331784151332358177649483819648417632" falls > between 913438523331814323877303020447676887284957839360 (partition 5) and > 1096126227998177188652763624537212264741949407232 (partition 6)? > > Please Riak experts help to clear my confusion here. Why partition 6, 7, 0 > are on the top 3 of the list? > > Appreciate in advance. > > > -donald > _______________________________________________ > 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
