feat: concurrent migration for postgres db

Author: serdarozerr

db/migrations/20260323092954_add_unique_constraint_to_sidecars.rb

@@ -1,10 +1,13 @@
 Sequel.migration do
+  no_transaction # required for concurrently option on postgres
+
   up do
     transaction do
       duplicates = self[:sidecars].
                    select(:app_guid, :name).
                    group(:app_guid, :name).
                    having { count(1) > 1 }
+
       duplicates.each do |dup|
         ids_to_remove = self[:sidecars].
                         where(app_guid: dup[:app_guid], name: dup[:name]).
@@ -15,19 +18,42 @@
 
         self[:sidecars].where(id: ids_to_remove).delete
       end
+    end
 
+    if database_type == :postgres
+      VCAP::Migration.with_concurrent_timeout(self) do
+        add_index :sidecars, %i[app_guid name],
+                  name: :sidecars_app_guid_name_index,
+                  unique: true,
+                  concurrently: true,
+                  if_not_exists: true
+      end
+    else
       alter_table(:sidecars) do
+        # rubocop:disable Sequel/ConcurrentIndex -- MySQL does not support concurrent index operations
         unless @db.indexes(:sidecars).key?(:sidecars_app_guid_name_index)
-          add_unique_constraint %i[app_guid name],
-                                name: :sidecars_app_guid_name_index
+          add_index %i[app_guid name], unique: true,
+                                       name: :sidecars_app_guid_name_index
         end
+        # rubocop:enable Sequel/ConcurrentIndex
       end
     end
   end
 
   down do
-    alter_table(:sidecars) do
-      drop_constraint(:sidecars_app_guid_name_index, type: :unique) if @db.indexes(:sidecars).key?(:sidecars_app_guid_name_index)
+    if database_type == :postgres
+      VCAP::Migration.with_concurrent_timeout(self) do
+        drop_index :sidecars, nil,
+                   name: :sidecars_app_guid_name_index,
+                   concurrently: true,
+                   if_exists: true
+      end
+    else
+      alter_table(:sidecars) do
+        # rubocop:disable Sequel/ConcurrentIndex -- MySQL does not support concurrent index operations
+        drop_index %i[app_guid name], name: :sidecars_app_guid_name_index if @db.indexes(:sidecars).key?(:sidecars_app_guid_name_index)
+        # rubocop:enable Sequel/ConcurrentIndex
+      end
     end
   end
 end