From 35b6898f7cb5223e1de4edc1b4539e05dfd83d41 Mon Sep 17 00:00:00 2001
From: Pavel <pavel.evst@gmail.com>
Date: Wed, 9 Nov 2016 01:10:16 +0800
Subject: [PATCH] Add ActiveRecord::Base.connection_pool.stat

---
 activerecord/CHANGELOG.md                     |  9 +++++++++
 .../abstract/connection_pool.rb               | 18 +++++++++++++++++
 .../test/cases/connection_pool_test.rb        | 20 +++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index d2adc530a4..dd2a1b4b19 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,12 @@
+*   Add `stat` method to `ActiveRecord::ConnectionAdapters::ConnectionPool`
+
+    Example:
+
+        ActiveRecord::Base.connection_pool.stat # =>
+        { size: 15, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }
+
+    *Pavel Evstigneev*
+
 *   Avoid `unscope(:order)` when `limit_value` is presented for `count`.
 
     If `limit_value` is presented, records fetching order is very important
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index e9ecb78e27..9727d63883 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -581,6 +581,24 @@ module ActiveRecord
         @available.num_waiting
       end
 
+      # Return connection pool's usage statistic
+      # Example:
+      #
+      #    ActiveRecord::Base.connection_pool.stat # => { size: 15, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }
+      def stat
+        synchronize do
+          {
+            size: size,
+            connections: @connections.size,
+            busy: @connections.count { |c| c.in_use? && c.owner.alive? },
+            dead: @connections.count { |c| c.in_use? && !c.owner.alive? },
+            idle: @connections.count { |c| !c.in_use? },
+            waiting: num_waiting_in_queue,
+            checkout_timeout: checkout_timeout
+          }
+        end
+      end
+
       private
         #--
         # this is unfortunately not concurrent
diff --git a/activerecord/test/cases/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb
index 3844f1eca2..b08e4f603c 100644
--- a/activerecord/test/cases/connection_pool_test.rb
+++ b/activerecord/test/cases/connection_pool_test.rb
@@ -526,6 +526,26 @@ module ActiveRecord
         end
       end
 
+      def test_connection_pool_stat
+        with_single_connection_pool do |pool|
+          pool.with_connection do |connection|
+            stats = pool.stat
+            assert_equal({ size: 1, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }, stats)
+          end
+
+          stats = pool.stat
+          assert_equal({ size: 1, connections: 1, busy: 0, dead: 0, idle: 1, waiting: 0, checkout_timeout: 5 }, stats)
+
+          Thread.new do
+            pool.checkout
+            Thread.current.kill
+          end.join
+
+          stats = pool.stat
+          assert_equal({ size: 1, connections: 1, busy: 0, dead: 1, idle: 0, waiting: 0, checkout_timeout: 5 }, stats)
+        end
+      end
+
       private
         def with_single_connection_pool
           one_conn_spec = ActiveRecord::Base.connection_pool.spec.dup