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# frozen_string_literal: true
require 'spec_helper'
RSpec.describe ::Gitlab::Database::LoadBalancing::ServiceDiscovery::Sampler do
let(:sampler) { described_class.new(max_replica_pools: max_replica_pools, seed: 100) }
let(:max_replica_pools) { 3 }
let(:address_class) { ::Gitlab::Database::LoadBalancing::ServiceDiscovery::Address }
let(:addresses) do
[
address_class.new("127.0.0.1", 6432),
address_class.new("127.0.0.1", 6433),
address_class.new("127.0.0.1", 6434),
address_class.new("127.0.0.1", 6435),
address_class.new("127.0.0.2", 6432),
address_class.new("127.0.0.2", 6433),
address_class.new("127.0.0.2", 6434),
address_class.new("127.0.0.2", 6435)
]
end
describe '#sample' do
it 'samples max_replica_pools addresses' do
expect(sampler.sample(addresses).count).to eq(max_replica_pools)
end
it 'samples random ports across all hosts' do
expect(sampler.sample(addresses)).to eq([
address_class.new("127.0.0.1", 6432),
address_class.new("127.0.0.2", 6435),
address_class.new("127.0.0.1", 6435)
])
end
it 'returns the same answer for the same input when called multiple times' do
result = sampler.sample(addresses)
expect(sampler.sample(addresses)).to eq(result)
expect(sampler.sample(addresses)).to eq(result)
end
it 'gives a consistent answer regardless of input ordering' do
expect(sampler.sample(addresses.reverse)).to eq(sampler.sample(addresses))
end
it 'samples fairly across all hosts' do
# Choose a bunch of different seeds to prove that it always chooses 2
# different ports from each host when selecting 4
(1..10).each do |seed|
sampler = described_class.new(max_replica_pools: 4, seed: seed)
result = sampler.sample(addresses)
expect(result.count { |r| r.hostname == "127.0.0.1" }).to eq(2)
expect(result.count { |r| r.hostname == "127.0.0.2" }).to eq(2)
end
end
context 'when input is an empty array' do
it 'returns an empty array' do
expect(sampler.sample([])).to eq([])
end
end
context 'when there are less replicas than max_replica_pools' do
let(:max_replica_pools) { 100 }
it 'returns the same addresses' do
expect(sampler.sample(addresses)).to eq(addresses)
end
end
context 'when max_replica_pools is nil' do
let(:max_replica_pools) { nil }
it 'returns the same addresses' do
expect(sampler.sample(addresses)).to eq(addresses)
end
end
end
end
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