util.dbuffer: Add efficient shortcuts for discard() in certain cases
If the buffer is already empty, nothing to do. If we're throwing away the
whole buffer, we can just empty it and avoid read_chunk() (which in turn
may collapse()). These shortcuts are much more efficient.
local function generate_ring(nodes, num_replicas, hash)
local new_ring = {};
for _, node_name in ipairs(nodes) do
for replica = 1, num_replicas do
local replica_hash = hash(node_name..":"..replica);
new_ring[replica_hash] = node_name;
table.insert(new_ring, replica_hash);
end
end
table.sort(new_ring);
return new_ring;
end
local hashring_methods = {};
local hashring_mt = {
__index = function (self, k)
-- Automatically build self.ring if it's missing
if k == "ring" then
local ring = generate_ring(self.nodes, self.num_replicas, self.hash);
rawset(self, "ring", ring);
return ring;
end
return rawget(hashring_methods, k);
end
};
local function new(num_replicas, hash_function)
return setmetatable({ nodes = {}, num_replicas = num_replicas, hash = hash_function }, hashring_mt);
end;
function hashring_methods:add_node(name)
self.ring = nil;
self.nodes[name] = true;
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;
table.insert(self.nodes, node_name);
end
end
return true;
end
function hashring_methods:remove_node(node_name)
self.ring = nil;
if self.nodes[node_name] then
for i, stored_node_name in ipairs(self.nodes) do
if node_name == stored_node_name then
self.nodes[node_name] = nil;
table.remove(self.nodes, i);
return true;
end
end
end
return false;
end
function hashring_methods:remove_nodes(nodes)
self.ring = nil;
for _, node_name in ipairs(nodes) do
self:remove_node(node_name);
end
end
function hashring_methods:clone()
local clone_hashring = new(self.num_replicas, self.hash);
clone_hashring:add_nodes(self.nodes);
return clone_hashring;
end
function hashring_methods:get_node(key)
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];
end
end
return self.ring[self.ring[1]];
end
return {
new = new;
}