prosody
071715a18394
util/hashring.lua

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util/hashring.lua @ 11769:071715a18394

mod_pubsub: Move reversal of item order in <items> Examples in XEP-0060 suggest that items should be listed in chronological order, but we get them from the archive in reverse order. However when requesting specific items by id the results keep that order and we don't want to flip it again. At some point it would likely be best to use the archive API directly instead of this util.cache-compatible wrapper.
author Kim Alvefur <zash@zash.se>
date Sun, 05 Sep 2021 18:42:44 +0200
parent 11208:96429946a742
child 12795:87424cbedc55
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rev   line source
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409ff72c501c util.hashring: Implementation of hashring data structure
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1 local function generate_ring(nodes, num_replicas, hash)
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2 local new_ring = {};
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3 for _, node_name in ipairs(nodes) do
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4 for replica = 1, num_replicas do
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5 local replica_hash = hash(node_name..":"..replica);
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6 new_ring[replica_hash] = node_name;
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7 table.insert(new_ring, replica_hash);
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8 end
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9 end
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10 table.sort(new_ring);
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11 return new_ring;
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12 end
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13
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14 local hashring_methods = {};
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15 local hashring_mt = {
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16 __index = function (self, k)
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17 -- Automatically build self.ring if it's missing
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18 if k == "ring" then
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19 local ring = generate_ring(self.nodes, self.num_replicas, self.hash);
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20 rawset(self, "ring", ring);
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21 return ring;
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22 end
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23 return rawget(hashring_methods, k);
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24 end
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25 };
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26
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27 local function new(num_replicas, hash_function)
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28 return setmetatable({ nodes = {}, num_replicas = num_replicas, hash = hash_function }, hashring_mt);
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29 end;
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30
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31 function hashring_methods:add_node(name)
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32 self.ring = nil;
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33 self.nodes[name] = true;
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34 table.insert(self.nodes, name);
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35 return true;
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36 end
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37
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38 function hashring_methods:add_nodes(nodes)
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39 self.ring = nil;
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40 for _, node_name in ipairs(nodes) do
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41 if not self.nodes[node_name] then
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42 self.nodes[node_name] = true;
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43 table.insert(self.nodes, node_name);
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44 end
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45 end
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46 return true;
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47 end
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48
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49 function hashring_methods:remove_node(node_name)
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50 self.ring = nil;
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51 if self.nodes[node_name] then
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52 for i, stored_node_name in ipairs(self.nodes) do
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53 if node_name == stored_node_name then
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54 self.nodes[node_name] = nil;
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55 table.remove(self.nodes, i);
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56 return true;
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57 end
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58 end
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59 end
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60 return false;
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61 end
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62
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63 function hashring_methods:remove_nodes(nodes)
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64 self.ring = nil;
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65 for _, node_name in ipairs(nodes) do
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66 self:remove_node(node_name);
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67 end
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68 end
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69
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70 function hashring_methods:clone()
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71 local clone_hashring = new(self.num_replicas, self.hash);
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72 clone_hashring:add_nodes(self.nodes);
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73 return clone_hashring;
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74 end
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75
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76 function hashring_methods:get_node(key)
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77 local key_hash = self.hash(key);
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78 for _, replica_hash in ipairs(self.ring) do
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79 if key_hash < replica_hash then
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80 return self.ring[replica_hash];
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81 end
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82 end
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83 return self.ring[self.ring[1]];
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84 end
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85
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86 return {
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87 new = new;
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88 }