Just create new hash instead of enforcing unique hash

app/jobs/one_time/generate_unique_heartbeat_hashes_job.rb

@@ -0,0 +1,20 @@
+class OneTime::GenerateUniqueHeartbeatHashesJob < ApplicationJob
+  queue_as :default
+
+  def perform
+    Heartbeat.find_each do |heartbeat|
+      heartbeat.send(:set_fields_hash!)
+      heartbeat.save!
+    end
+
+    # error if any two heartbeats have the same fields_hash
+    duplicates = false
+
+    Heartbeat.group(:fields_hash).having("count(*) > 1").count.each do |fields_hash, count|
+      puts "Duplicate fields_hash: #{fields_hash} (count: #{count})"
+      duplicates = true
+    end
+
+    raise "Duplicate in fields_hash" if duplicates
+  end
+end

db/migrate/20250305061242_uniqueness_index_to_hash_on_heartbeats.rb

@@ -24,28 +24,11 @@ class UniquenessIndexToHashOnHeartbeats < ActiveRecord::Migration[8.0]
       :is_write
     ]
 
-    add_column :heartbeats, :fields_hash, :text
-
-    Heartbeat.find_each do |heartbeat|
-      heartbeat.send(:set_fields_hash!)
-      heartbeat.save!
-    end
-
-    # error if any two heartbeats have the same fields_hash
-    duplicates = false
-    Heartbeat.group(:fields_hash).having("count(*) > 1").count.each do |fields_hash, count|
-      puts "Duplicate fields_hash: #{fields_hash} (count: #{count})"
-      duplicates = true
-    end
-
-    raise "Duplicate in fields_hash" if duplicates
-
-    change_column_null :heartbeats, :fields_hash, false
-    add_index :heartbeats, :fields_hash, unique: true
-
     # clean up the index from ./20250303180842_create_heartbeats.rb
     remove_index :heartbeats,
                  attributes,
                  unique: true
+
+    add_column :heartbeats, :fields_hash, :text
   end
 end