Hi Charlie, That really helps to clear the confusion. Thanks again!
Then it comes to the next question :-) Just curious to know: is there a special reason why using the end value as the partition's name? Normally, most people I think would pick the beginning value as the partition's name in common logic. And a second question related to the above question is how this end value is picked: partition named "0" is actually ending with number 0, and so forth for the other partitions. This is like the 160-bit space got right-shifted one number relative to 0-started numbering system. Is there a special reason for it in Riak, or simply want to use 1-started numbering system. wr, donald On Mon, Jan 28, 2013 at 3:21 PM, Charlie Voiselle <cvoise...@basho.com>wrote: > 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 > > >
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