diff --git a/app/controllers/clock_ins_controller.rb b/app/controllers/clock_ins_controller.rb
index 448ffc5..dbcb8b6 100644
--- a/app/controllers/clock_ins_controller.rb
+++ b/app/controllers/clock_ins_controller.rb
@@ -1,14 +1,16 @@
 class ClockInsController < ApplicationController
   include UserFinder
+  include Retryable
 
   def upsert
     current_time = Time.now
 
-    begin
+    with_retry do
       ActiveRecord::Base.transaction do
         last_unused_clock_in = ClockIn.where(
-          user_id: @user.id, 
-          is_clocked_out: false)
+          is_clocked_out: false,
+          user_id: @user.id
+          )
           .order(clocked_in_at: :desc)
           .limit(1)
           .lock(true)
@@ -27,14 +29,12 @@ def upsert
         else
           ClockIn.create!(
             user_id: @user.id,
-            clocked_in_at: Time.now
+            clocked_in_at: current_time
           )
 
           render_success(@user.clock_ins_json, I18n.t('success.messages.clock_in_success'))
         end
       end
-    rescue ActiveRecord::ActiveRecordError => e
-      render_error(:unprocessable_entity, e.message)
     end
   end
 
diff --git a/app/controllers/concerns/retryable.rb b/app/controllers/concerns/retryable.rb
new file mode 100644
index 0000000..b738539
--- /dev/null
+++ b/app/controllers/concerns/retryable.rb
@@ -0,0 +1,28 @@
+module Retryable
+  MAX_RETRIES = 3
+  RETRY_DELAY = 0.5 # seconds
+
+  def with_retry(max_retries: MAX_RETRIES, delay: RETRY_DELAY)
+    attempts = 0
+
+    begin
+      yield
+    rescue ActiveRecord::Deadlocked => e
+      attempts += 1
+      Rails.logger.warn("Retryable Error: #{e.class} - #{e.message}. Attempt #{attempts} of #{max_retries}.")
+      if attempts < max_retries
+        sleep(delay * attempts)
+        retry
+      else
+        Rails.logger.error("Retries exhausted for #{e.class}: #{e.message}")
+        raise e
+      end
+    rescue ActiveRecord::ActiveRecordError => e
+      Rails.logger.error("ActiveRecord Error: #{e.class} - #{e.message}")
+      render_error(:unprocessable_entity, e.message)
+    rescue StandardError => e
+      Rails.logger.error("Unexpected Error: #{e.class} - #{e.message}")
+      render_error(:internal_server_error, e.message)
+    end
+  end
+end
\ No newline at end of file
diff --git a/db/migrate/20250102060751_add_index_to_user_follows_on_follower_and_followee.rb b/db/migrate/20250102060751_add_index_to_user_follows_on_follower_and_followee.rb
index f415519..36b627f 100644
--- a/db/migrate/20250102060751_add_index_to_user_follows_on_follower_and_followee.rb
+++ b/db/migrate/20250102060751_add_index_to_user_follows_on_follower_and_followee.rb
@@ -4,6 +4,6 @@ def up
   end
 
   def down
-    add_index :user_follows, name: 'index_user_follows_on_follower_id_and_followee_id'
+    remove_index :user_follows, name: 'index_user_follows_on_follower_id_and_followee_id'
   end
 end
diff --git a/db/migrate/20250103014113_add_index_clock_ins_on_is_clocked_out_and_user_id.rb b/db/migrate/20250103014113_add_index_clock_ins_on_is_clocked_out_and_user_id.rb
new file mode 100644
index 0000000..be65c23
--- /dev/null
+++ b/db/migrate/20250103014113_add_index_clock_ins_on_is_clocked_out_and_user_id.rb
@@ -0,0 +1,11 @@
+class AddIndexClockInsOnIsClockedOutAndUserId < ActiveRecord::Migration[7.0]
+  def up
+    add_index :clock_ins, [:is_clocked_out, :user_id], name: 'index_clock_ins_on_is_clocked_out_and_user_id'
+    remove_index :clock_ins, [:user_id, :clocked_in_at]
+  end
+
+  def down
+    remove_index :user_follows, name: 'index_clock_ins_on_is_clocked_out_and_user_id'
+    add_index :clock_ins, [:user_id, :clocked_in_at]
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index bfe3597..7cfcca2 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2025_01_02_060751) do
+ActiveRecord::Schema[7.0].define(version: 2025_01_03_014113) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -18,7 +18,7 @@
     t.bigint "user_id", null: false
     t.datetime "clocked_in_at", null: false
     t.boolean "is_clocked_out", default: false, null: false
-    t.index ["user_id", "clocked_in_at"], name: "index_clock_ins_on_user_id_and_clocked_in_at"
+    t.index ["is_clocked_out", "user_id"], name: "index_clock_ins_on_is_clocked_out_and_user_id"
     t.index ["user_id"], name: "index_clock_ins_on_user_id"
   end
 
diff --git a/system-design/README.md b/system-design/README.md
index ece3760..1c27ae7 100644
--- a/system-design/README.md
+++ b/system-design/README.md
@@ -23,6 +23,7 @@ This document contains the details of ideas and implementation for time tracker
 3. For any clock-ins, every second clock-in will be considered a clock out for the last clock-in for us to calculate sleep record.
 4. Since the feature is quite simple, most part is enough with simple error message, but it is better to implement proper logging.
 5. Need proper error handling because ActiveModel::Error's full_messages return message with key.
+6. Need to implement retry mechanism for concurrent requests to mitigate deadlocks on locking.
 
 ## Non-Functional Requirements
 1. **Scalability**