FEATURE: Drop "backup" schema 7 days after restore

The "backup" schema is used to rollback a failed restore. It isn't useful after a longer period of time and turns into a waste of disk space.

app/jobs/scheduled/drop_backup_schema.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Jobs
+  class DropBackupSchema < ::Jobs::Scheduled
+    every 1.day
+
+    def execute(_)
+      BackupRestore::DatabaseRestorer.drop_backup_schema
+    end
+  end
+end

app/models/backup_metadata.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class BackupMetadata < ActiveRecord::Base
+  LAST_RESTORE_DATE = "last_restore_date"
+
   def self.value_for(name)
     where(name: name).pluck_first(:value).presence
   end

lib/backup_restore/database_restorer.rb

@@ -8,6 +8,7 @@ module BackupRestore
 
     MAIN_SCHEMA = "public"
     BACKUP_SCHEMA = "backup"
+    DROP_BACKUP_SCHEMA_AFTER_DAYS = 7
 
     def initialize(logger, current_db)
       @logger = logger
@@ -25,6 +26,8 @@ module BackupRestore
       restore_dump
       migrate_database
       reconnect_database
+
+      self.class.update_last_restore_date
     end
 
     def rollback
@@ -42,6 +45,20 @@ module BackupRestore
       drop_created_discourse_functions
     end
 
+    def self.drop_backup_schema
+      if backup_schema_dropable?
+        ActiveRecord::Base.connection.drop_schema(BACKUP_SCHEMA)
+      end
+    end
+
+    def self.update_last_restore_date
+      BackupMetadata.where(name: BackupMetadata::LAST_RESTORE_DATE).delete_all
+      BackupMetadata.create!(
+        name: BackupMetadata::LAST_RESTORE_DATE,
+        value: Time.zone.now.iso8601
+      )
+    end
+
     protected
 
     def restore_dump
@@ -178,5 +195,20 @@ module BackupRestore
     rescue => ex
       log "Something went wrong while dropping functions from the discourse_functions schema", ex
     end
+
+    def self.backup_schema_dropable?
+      return false unless ActiveRecord::Base.connection.schema_exists?(BACKUP_SCHEMA)
+
+      last_restore_date = BackupMetadata.value_for(BackupMetadata::LAST_RESTORE_DATE)
+
+      if last_restore_date.present?
+        last_restore_date = Time.zone.parse(last_restore_date)
+        return last_restore_date + DROP_BACKUP_SCHEMA_AFTER_DAYS.days < Time.zone.now
+      end
+
+      update_last_restore_date
+      false
+    end
+    private_class_method :backup_schema_dropable?
   end
 end

spec/lib/backup_restore/database_restorer_spec.rb

@@ -67,6 +67,14 @@ describe BackupRestore::DatabaseRestorer do
       subject.restore("foo.sql")
     end
 
+    it "stores the date of the last restore" do
+      date_string = "2020-01-10T17:38:27Z"
+      freeze_time(Time.parse(date_string))
+      execute_stubbed_restore
+
+      expect(BackupMetadata.value_for(BackupMetadata::LAST_RESTORE_DATE)).to eq(date_string)
+    end
+
     context "with real psql" do
       after do
         psql = BackupRestore::DatabaseRestorer.psql_command
@@ -176,4 +184,53 @@ describe BackupRestore::DatabaseRestorer do
       subject.clean_up
     end
   end
+
+  describe ".drop_backup_schema" do
+    subject { BackupRestore::DatabaseRestorer }
+
+    context "when no backup schema exists" do
+      it "doesn't do anything" do
+        ActiveRecord::Base.connection.expects(:schema_exists?).with("backup").returns(false)
+        ActiveRecord::Base.connection.expects(:drop_schema).never
+
+        subject.drop_backup_schema
+      end
+    end
+
+    context "when a backup schema exists" do
+      before do
+        ActiveRecord::Base.connection.expects(:schema_exists?).with("backup").returns(true)
+      end
+
+      it "drops the schema when the last restore was long ago" do
+        ActiveRecord::Base.connection.expects(:drop_schema).with("backup")
+
+        freeze_time(8.days.ago) do
+          subject.update_last_restore_date
+        end
+
+        subject.drop_backup_schema
+      end
+
+      it "doesn't drop the schema when the last restore was recently" do
+        ActiveRecord::Base.connection.expects(:drop_schema).with("backup").never
+
+        freeze_time(6.days.ago) do
+          subject.update_last_restore_date
+        end
+
+        subject.drop_backup_schema
+      end
+
+      it "stores the current date when there is no record of the last restore" do
+        ActiveRecord::Base.connection.expects(:drop_schema).with("backup").never
+
+        date_string = "2020-01-08T17:38:27Z"
+        freeze_time(Time.parse(date_string))
+
+        subject.drop_backup_schema
+        expect(BackupMetadata.value_for(BackupMetadata::LAST_RESTORE_DATE)).to eq(date_string)
+      end
+    end
+  end
 end