Add metrics for connection pool usage v3 (#307)

l

integration_test/connection_pool/metrics_test.exs

@@ -0,0 +1,169 @@
+defmodule TestPoolMetrics do
+  import TestHelpers
+
+  use ExUnit.Case, async: true
+
+  alias TestPool, as: P
+  alias TestAgent, as: A
+  alias TestQuery, as: Q
+  alias TestResult, as: R
+
+  test "considers checkin/checkout in metrics when ready" do
+    stack = [
+      {:ok, :state},
+      fn _, _, _, _ ->
+        receive do
+          :continue -> {:ok, %Q{}, %R{}, :state}
+        end
+      end
+    ]
+
+    {:ok, agent} = A.start_link(stack)
+    {:ok, pool} = P.start_link(agent: agent, parent: self())
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    query =
+      spawn_link(fn ->
+        Process.put(:agent, agent)
+        assert P.execute(pool, %Q{}, [:client])
+      end)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 0}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    send(query, :continue)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    assert [
+             connect: [_],
+             handle_execute: [%Q{}, [:client], _, :state]
+           ] = A.record(agent)
+  end
+
+  test "considers idle connections on idle timeout in metrics" do
+    stack = [
+      {:ok, :state},
+      {:ok, :state}
+    ]
+
+    idle_interval = 100
+
+    {:ok, agent} = A.start_link(stack)
+    {:ok, pool} = P.start_link(agent: agent, parent: self(), idle_interval: idle_interval)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    :timer.sleep(idle_interval)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    assert [
+             connect: [_],
+             ping: [:state]
+           ] = A.record(agent)
+  end
+
+  test "considers enqueue/dequeue in metrics when busy" do
+    stack = [
+      {:ok, :state},
+      {:ok, :state},
+      fn _, _, _, _ ->
+        receive do
+          :continue -> {:ok, %Q{}, %R{}, :state}
+        end
+      end,
+      fn _, _, _, _ ->
+        receive do
+          :continue -> {:ok, %Q{}, %R{}, :state}
+        end
+      end,
+      fn _, _, _, _ ->
+        receive do
+          :continue -> {:ok, %Q{}, %R{}, :state}
+        end
+      end
+    ]
+
+    {:ok, agent} = A.start_link(stack)
+    {:ok, pool} = P.start_link(agent: agent, parent: self(), pool_size: 2)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 2}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    run_query = fn ->
+      spawn_link(fn ->
+        Process.put(:agent, agent)
+        assert P.execute(pool, %Q{}, [:client])
+      end)
+    end
+
+    queries = [run_query.()]
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    queries = [run_query.() | queries]
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 0}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    queries = [run_query.() | queries]
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 1, ready_conn_count: 0}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    [query3, query2, query1] = queries
+    send(query1, :continue)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 0}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    send(query2, :continue)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 1}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    send(query3, :continue)
+
+    poll(fn ->
+      assert [%{source: {:pool, ^pool}, checkout_queue_length: 0, ready_conn_count: 2}] =
+               DBConnection.get_connection_metrics(pool)
+    end)
+
+    assert [
+             connect: [_],
+             connect: [_],
+             handle_execute: [%Q{}, [:client], _, :state],
+             handle_execute: [%Q{}, [:client], _, :state],
+             handle_execute: [%Q{}, [:client], _, :state]
+           ] = A.record(agent)
+  end
+end