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Name consistency: CoC 'locator', variable name = L

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Scott Lystig Fritchie 2015-10-17 16:47:00 +09:00
parent 1485fa416f
commit 8ab9d3ee50
1 changed files with 13 additions and 13 deletions
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doc/cluster-of-clusters/name-game-sketch.org
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@ -145,12 +145,12 @@ According to ~Map~, the value of
~rs_hash_with_float(0.05,Map) = Cluster1~. ~rs_hash_with_float(0.05,Map) = Cluster1~.
Similarly, ~rs_hash_with_float(0.26,Map) = Cluster4~. Similarly, ~rs_hash_with_float(0.26,Map) = Cluster4~.
* 4. An additional assumption: clients will want some control over file placement * 4. An additional assumption: clients will want some control over file location
We will continue to use the 4-cluster diagram from the previous We will continue to use the 4-cluster diagram from the previous
section. section.
** Our new assumption: client control over initial file placement ** Our new assumption: client control over initial file location
The CoC management scheme may decide that files need to migrate to The CoC management scheme may decide that files need to migrate to
other clusters. The reason could be for storage load or I/O load other clusters. The reason could be for storage load or I/O load
@ -226,7 +226,7 @@ we need?
- ~p~ = file prefix, chosen by the CoC client. - ~p~ = file prefix, chosen by the CoC client.
- ~T~ = the target CoC member/Cluster ID chosen by the CoC client at the time of ~append()~ - ~T~ = the target CoC member/Cluster ID chosen by the CoC client at the time of ~append()~
- ~u~ = the Machi file server unique opaque file name suffix, e.g. a GUID string - ~u~ = the Machi file server unique opaque file name suffix, e.g. a GUID string
- ~K~ = the CoC placement key - ~L~ = the CoC locator
- ~N~ = the CoC namespace - ~N~ = the CoC namespace
- ~F~ = a Machi file name - ~F~ = a Machi file name
@ -235,21 +235,21 @@ we need?
1. CoC client chooses ~p~, ~T~, and ~N~ (i.e., the file prefix, target 1. CoC client chooses ~p~, ~T~, and ~N~ (i.e., the file prefix, target
cluster, and target cluster namespace) cluster, and target cluster namespace)
2. CoC client knows the CoC ~Map~ for namespace ~N~. 2. CoC client knows the CoC ~Map~ for namespace ~N~.
3. CoC client choose some value ~K~ such that 3. CoC client choose some CoC locator value ~L~ such that
~rs_hash_with_float(K,Map) = T~ (see below). ~rs_hash_with_float(L,Map) = T~ (see below).
4. CoC client sends its request to cluster 4. CoC client sends its request to cluster
~T~: ~append_chunk(p,K,N,...) -> {ok,p.K.N.u,ByteOffset}~ ~T~: ~append_chunk(p,L,N,...) -> {ok,p.L.N.u,ByteOffset}~
5. CoC stores/uses the file name ~F = p.K.N.u~. 5. CoC stores/uses the file name ~F = p.L.N.u~.
** The details: CoC file read ** The details: CoC file read
1. CoC client knows the file name ~F = p.K.N.u~ and parses it to find 1. CoC client knows the file name ~F = p.L.N.u~ and parses it to find
the values of ~K~ and ~N~. the values of ~L~ and ~N~.
2. CoC client knows the CoC ~Map~ for type ~N~. 2. CoC client knows the CoC ~Map~ for type ~N~.
3. CoC calculates ~rs_hash_with_float(K,Map) = T~ 3. CoC calculates ~rs_hash_with_float(L,Map) = T~
4. CoC client sends request to cluster ~T~: ~read_chunk(F,...) ->~ ... success! 4. CoC client sends request to cluster ~T~: ~read_chunk(F,...) ->~ ... success!
** The details: calculating 'K' (the CoC placement key) to match a desired target cluster ** The details: calculating 'L' (the CoC locator) to match a desired target cluster
1. We know ~Map~, the current CoC mapping for a CoC namespace ~N~. 1. We know ~Map~, the current CoC mapping for a CoC namespace ~N~.
2. We look inside of ~Map~, and we find all of the unit interval ranges 2. We look inside of ~Map~, and we find all of the unit interval ranges
@ -258,9 +258,9 @@ we need?
3. In our example, ~T=Cluster2~. The example ~Map~ contains a single 3. In our example, ~T=Cluster2~. The example ~Map~ contains a single
unit interval range for ~Cluster2~, ~[(0.33,0.58]]~. unit interval range for ~Cluster2~, ~[(0.33,0.58]]~.
4. Choose a uniformly random number ~r~ on the unit interval. 4. Choose a uniformly random number ~r~ on the unit interval.
5. Calculate placement key ~K~ by mapping ~r~ onto the concatenation 5. Calculate locator ~L~ by mapping ~r~ onto the concatenation
of the CoC hash space range intervals in ~MapList~. For example, of the CoC hash space range intervals in ~MapList~. For example,
if ~r=0.5~, then ~K = 0.33 + 0.5*(0.58-0.33) = 0.455~, which is if ~r=0.5~, then ~L = 0.33 + 0.5*(0.58-0.33) = 0.455~, which is
exactly in the middle of the ~(0.33,0.58]~ interval. exactly in the middle of the ~(0.33,0.58]~ interval.
* 8. File migration (a.k.a. rebalancing/reparitioning/resharding/redistribution) * 8. File migration (a.k.a. rebalancing/reparitioning/resharding/redistribution)