Copilot commented on code in PR #3426:
URL: https://github.com/apache/brpc/pull/3426#discussion_r3700954669
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test/brpc_load_balancer_unittest.cpp:
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@@ -1026,6 +1026,55 @@ TEST_F(LoadBalancerTest, weighted_randomized) {
}
}
+TEST_F(LoadBalancerTest, weighted_randomized_equal_weight) {
+ // With equal weights every server must get the same share of the traffic.
+ // The tolerance of `weighted_randomized` above is +/-2x, which is too
loose
+ // to catch a single misplaced slot, so check the distribution tightly
here.
+ const char* servers[] = {
+ "10.92.115.19:8831",
+ "10.42.108.25:8832",
+ "10.36.150.31:8833",
+ "10.36.150.32:8899"
+ };
+ brpc::policy::WeightedRandomizedLoadBalancer wrlb;
+ for (size_t i = 0; i < ARRAY_SIZE(servers); ++i) {
+ butil::EndPoint dummy;
+ ASSERT_EQ(0, str2endpoint(servers[i], &dummy));
+ brpc::ServerId id(8888);
+ brpc::SocketOptions options;
+ options.remote_side = dummy;
+ options.user = new SaveRecycle;
+ ASSERT_EQ(0, brpc::Socket::Create(options, &id.id));
+ id.tag = "1";
+ ASSERT_TRUE(wrlb.AddServer(id));
+ }
+
+ std::map<butil::EndPoint, size_t> select_result;
+ brpc::SocketUniquePtr ptr;
+ brpc::LoadBalancer::SelectIn in = { 0, false, false, 0u, NULL };
+ brpc::LoadBalancer::SelectOut out(&ptr);
+ const int run_times = 40000;
+ for (int i = 0; i < run_times; ++i) {
+ ASSERT_EQ(0, wrlb.SelectServer(in, &out));
+ ++select_result[ptr->remote_side()];
+ }
+
+ // Every server must be selected at least once, in particular the one added
+ // last, which owns the largest prefix sum.
+ ASSERT_EQ(ARRAY_SIZE(servers), select_result.size());
+ const double expect_rate = 1.0 / ARRAY_SIZE(servers);
+ for (const auto& result : select_result) {
+ const double actual_rate = result.second * 1.0 / run_times;
+ std::cout << result.first << " select_times=" << result.second
+ << " actual_rate=" << actual_rate
+ << " expect_rate=" << expect_rate << std::endl;
+ // 0.9x ~ 1.1x of the expected rate, which is more than 20 standard
+ // deviations away from the mean at this number of runs.
Review Comment:
The comment about the tolerance being “more than 20 standard deviations” is
numerically incorrect for this test setup (run_times=40000, p=0.25). The
0.9x~1.1x band is ~11.5σ wide, not >20σ. Please update the comment to avoid
misleading readers.
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