util.hashring: Support associating arbitrary data with nodes
In this API, a 'node' is always a simple text string. Sometimes the caller may
have a more complex structure representing a node, but the hash ring is really
only concerned with the node's name.
This API change allows :add_nodes() to take a table of `node_name = value`
pairs, as well as the simple array of node names previously accepted.
The 'value' of the selected node is returned as a new second result from
:get_node().
If no value is passed when a node is added, it defaults to `true` (as before,
but this was never previously exposed).
--- a/spec/util_hashring_spec.lua Fri Dec 02 20:27:32 2022 +0000
+++ b/spec/util_hashring_spec.lua Fri Dec 02 20:32:36 2022 +0000
@@ -83,4 +83,11 @@
end
end);
+ it("should support values associated with nodes", function ()
+ local r = hashring.new(128, sha256);
+ r:add_node("node1", { a = 1 });
+ local node, value = r:get_node("foo");
+ assert.is_equal("node1", node);
+ assert.same({ a = 1 }, value);
+ end);
end);
--- a/util/hashring.lua Fri Dec 02 20:27:32 2022 +0000
+++ b/util/hashring.lua Fri Dec 02 20:32:36 2022 +0000
@@ -1,3 +1,5 @@
+local it = require "util.iterators";
+
local function generate_ring(nodes, num_replicas, hash)
local new_ring = {};
for _, node_name in ipairs(nodes) do
@@ -28,18 +30,22 @@
return setmetatable({ nodes = {}, num_replicas = num_replicas, hash = hash_function }, hashring_mt);
end;
-function hashring_methods:add_node(name)
+function hashring_methods:add_node(name, value)
self.ring = nil;
- self.nodes[name] = true;
+ self.nodes[name] = value == nil and true or value;
table.insert(self.nodes, name);
return true;
end
function hashring_methods:add_nodes(nodes)
self.ring = nil;
- for _, node_name in ipairs(nodes) do
- if not self.nodes[node_name] then
- self.nodes[node_name] = true;
+ local iter = pairs;
+ if nodes[1] then -- simple array?
+ iter = it.values;
+ end
+ for node_name, node_value in iter(nodes) do
+ if self.nodes[node_name] == nil then
+ self.nodes[node_name] = node_value == nil and true or node_value;
table.insert(self.nodes, node_name);
end
end
@@ -48,7 +54,7 @@
function hashring_methods:remove_node(node_name)
self.ring = nil;
- if self.nodes[node_name] then
+ if self.nodes[node_name] ~= nil then
for i, stored_node_name in ipairs(self.nodes) do
if node_name == stored_node_name then
self.nodes[node_name] = nil;
@@ -69,18 +75,26 @@
function hashring_methods:clone()
local clone_hashring = new(self.num_replicas, self.hash);
- clone_hashring:add_nodes(self.nodes);
+ for node_name, node_value in pairs(self.nodes) do
+ clone_hashring.nodes[node_name] = node_value;
+ end
+ clone_hashring.ring = nil;
return clone_hashring;
end
function hashring_methods:get_node(key)
+ local node;
local key_hash = self.hash(key);
for _, replica_hash in ipairs(self.ring) do
if key_hash < replica_hash then
- return self.ring[replica_hash];
+ node = self.ring[replica_hash];
+ break;
end
end
- return self.ring[self.ring[1]];
+ if not node then
+ node = self.ring[self.ring[1]];
+ end
+ return node, self.nodes[node];
end
return {