Make many migrations rollbackable29656-fix-rollback-job

Don't try to create the index if it already exist. It's possible that a
previous rollback did not remove the index since the index is not
dropped on MySQL because MySQL would also drop the foreign key in that
case, see f67d8eb1da.

Signed-off-by: Rémy Coutable <remy@rymai.me>

41 files changed, 292 insertions, 71 deletions

diff --git a/db/migrate/20140914113604_add_members_table.rb b/db/migrate/20140914113604_add_members_table.rb
index 0f76bb0ef79..e03c5b0af39 100644
--- a/db/migrate/20140914113604_add_members_table.rb
+++ b/db/migrate/20140914113604_add_members_table.rb
@@ -2,7 +2,7 @@
 class AddMembersTable < ActiveRecord::Migration
   DOWNTIME = false
 
-  def change
+  def up
     create_table :members do |t|
       t.integer :access_level, null: false
       t.integer :source_id,    null: false
@@ -19,4 +19,8 @@ class AddMembersTable < ActiveRecord::Migration
     add_index :members, :access_level
     add_index :members, [:source_id, :source_type]
   end
+
+  def down
+    drop_table :members
+  end
 end
diff --git a/db/migrate/20141118150935_add_audit_event.rb b/db/migrate/20141118150935_add_audit_event.rb
index 52d70b4a0ac..4be4d835e28 100644
--- a/db/migrate/20141118150935_add_audit_event.rb
+++ b/db/migrate/20141118150935_add_audit_event.rb
@@ -2,7 +2,7 @@
 class AddAuditEvent < ActiveRecord::Migration
   DOWNTIME = false
 
-  def change
+  def up
     create_table :audit_events do |t|
       t.integer :author_id, null: false
       t.string  :type, null: false
@@ -22,4 +22,8 @@ class AddAuditEvent < ActiveRecord::Migration
     add_index :audit_events, :type
     add_index :audit_events, [:entity_id, :entity_type]
   end
+
+  def down
+    drop_table :audit_events
+  end
 end
diff --git a/db/migrate/20150206181414_add_index_to_created_at.rb b/db/migrate/20150206181414_add_index_to_created_at.rb
index a161fad79dc..3f40062e0f8 100644
--- a/db/migrate/20150206181414_add_index_to_created_at.rb
+++ b/db/migrate/20150206181414_add_index_to_created_at.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddIndexToCreatedAt < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index "users", [:created_at, :id]
     add_index "members", [:created_at, :id]
     add_index "projects", [:created_at, :id]
@@ -14,4 +16,20 @@ class AddIndexToCreatedAt < ActiveRecord::Migration
     add_index "web_hooks", [:created_at, :id]
     add_index "snippets", [:created_at, :id]
   end
+
+  def down
+    # These one is removed by RemoveRedundantIndexes
+    remove_index :snippets, column: [:created_at, :id] if index_exists?(:snippets, [:created_at, :id])
+    remove_index :web_hooks, column: [:created_at, :id] if index_exists?(:web_hooks, [:created_at, :id])
+    remove_index :keys, column: [:created_at, :id] if index_exists?(:keys, [:created_at, :id])
+    remove_index :identities, column: [:created_at, :id] if index_exists?(:identities, [:created_at, :id])
+    remove_index :notes, column: [:created_at, :id] if index_exists?(:notes, [:created_at, :id])
+    remove_index :namespaces, column: [:created_at, :id] if index_exists?(:namespaces, [:created_at, :id])
+    remove_index :milestones, column: [:created_at, :id] if index_exists?(:milestones, [:created_at, :id])
+    remove_index :merge_requests, column: [:created_at, :id] if index_exists?(:merge_requests, [:created_at, :id])
+    remove_index :issues, column: [:created_at, :id] if index_exists?(:issues, [:created_at, :id])
+    remove_index :projects, column: [:created_at, :id] if index_exists?(:projects, [:created_at, :id])
+    remove_index :members, column: [:created_at, :id] if index_exists?(:members, [:created_at, :id])
+    remove_index :users, column: [:created_at, :id] if index_exists?(:users, [:created_at, :id])
+  end
 end
diff --git a/db/migrate/20150209222013_add_missing_index.rb b/db/migrate/20150209222013_add_missing_index.rb
index 18e3ac2cbbb..84a5716edcc 100644
--- a/db/migrate/20150209222013_add_missing_index.rb
+++ b/db/migrate/20150209222013_add_missing_index.rb
@@ -1,6 +1,13 @@
 # rubocop:disable all
 class AddMissingIndex < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index "services", [:created_at, :id]
   end
+
+  def down
+    # This one is removed by RemoveRedundantIndexes
+    remove_index :services, column: [:created_at, :id] if index_exists?(:services, [:created_at, :id])
+  end
 end
diff --git a/db/migrate/20150211174341_allow_null_in_services_project_id.rb b/db/migrate/20150211174341_allow_null_in_services_project_id.rb
index fea95c79adf..6cad14ff104 100644
--- a/db/migrate/20150211174341_allow_null_in_services_project_id.rb
+++ b/db/migrate/20150211174341_allow_null_in_services_project_id.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class AllowNullInServicesProjectId < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     change_column :services, :project_id, :integer, null: true
   end
+
+  def down
+    change_column :services, :project_id, :integer, null: false
+  end
 end
diff --git a/db/migrate/20150425164649_add_taggings_counter_cache_to_tags.acts_as_taggable_on_engine.rb b/db/migrate/20150425164649_add_taggings_counter_cache_to_tags.acts_as_taggable_on_engine.rb
index 1568d2dd4ce..a5d43577982 100644
--- a/db/migrate/20150425164649_add_taggings_counter_cache_to_tags.acts_as_taggable_on_engine.rb
+++ b/db/migrate/20150425164649_add_taggings_counter_cache_to_tags.acts_as_taggable_on_engine.rb
@@ -1,16 +1,20 @@
 # rubocop:disable all
 # This migration comes from acts_as_taggable_on_engine (originally 3)
 class AddTaggingsCounterCacheToTags < ActiveRecord::Migration
-  def self.up
+  DOWNTIME = false
+
+  def up
     add_column :tags, :taggings_count, :integer, default: 0
 
+    return unless ActsAsTaggableOn.tags_counter
+
     ActsAsTaggableOn::Tag.reset_column_information
     ActsAsTaggableOn::Tag.find_each do |tag|
       ActsAsTaggableOn::Tag.reset_counters(tag.id, :taggings)
     end
   end
 
-  def self.down
+  def down
     remove_column :tags, :taggings_count
   end
 end
diff --git a/db/migrate/20150817163600_deduplicate_user_identities.rb b/db/migrate/20150817163600_deduplicate_user_identities.rb
index b0cfad7d20f..6f4cc549cac 100644
--- a/db/migrate/20150817163600_deduplicate_user_identities.rb
+++ b/db/migrate/20150817163600_deduplicate_user_identities.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class DeduplicateUserIdentities < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     execute 'DROP TABLE IF EXISTS tt_migration_DeduplicateUserIdentities;'
     execute 'CREATE TABLE tt_migration_DeduplicateUserIdentities AS SELECT id,provider,user_id FROM identities;'
     execute 'DELETE FROM identities WHERE id NOT IN ( SELECT MIN(id) FROM tt_migration_DeduplicateUserIdentities GROUP BY user_id, provider);'
@@ -9,7 +11,5 @@ class DeduplicateUserIdentities < ActiveRecord::Migration
 
   def down
     # This is an irreversible migration;
-    # If someone is trying to rollback for other reasons, we should not throw an Exception.
-    # raise ActiveRecord::IrreversibleMigration
   end
 end
diff --git a/db/migrate/20150826001931_add_ci_tables.rb b/db/migrate/20150826001931_add_ci_tables.rb
index d1f8506d1fe..0ce39843ae8 100644
--- a/db/migrate/20150826001931_add_ci_tables.rb
+++ b/db/migrate/20150826001931_add_ci_tables.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddCiTables < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     create_table "ci_application_settings", force: true do |t|
       t.boolean  "all_broken_builds"
       t.boolean  "add_pusher"
@@ -188,4 +190,21 @@ class AddCiTables < ActiveRecord::Migration
       t.datetime "updated_at"
     end
   end
+
+  def down
+    drop_table :ci_application_settings
+    drop_table :ci_builds
+    drop_table :ci_commits
+    drop_table :ci_events
+    drop_table :ci_jobs
+    drop_table :ci_projects
+    drop_table :ci_runner_projects
+    drop_table :ci_runners
+    drop_table :ci_services
+    drop_table :ci_sessions
+    drop_table :ci_trigger_requests
+    drop_table :ci_triggers
+    drop_table :ci_variables
+    drop_table :ci_web_hooks
+  end
 end
diff --git a/db/migrate/20150914215247_add_ci_tags.rb b/db/migrate/20150914215247_add_ci_tags.rb
index b647bc9c8a2..a69252f2530 100644
--- a/db/migrate/20150914215247_add_ci_tags.rb
+++ b/db/migrate/20150914215247_add_ci_tags.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddCiTags < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     create_table "ci_taggings", force: true do |t|
       t.integer  "tag_id"
       t.integer  "taggable_id"
@@ -21,4 +23,9 @@ class AddCiTags < ActiveRecord::Migration
 
     add_index "ci_tags", ["name"], name: "index_ci_tags_on_name", unique: true, using: :btree
   end
+
+  def down
+    drop_table :ci_tags
+    drop_table :ci_taggings
+  end
 end
diff --git a/db/migrate/20150915001905_enable_ssl_verification_by_default.rb b/db/migrate/20150915001905_enable_ssl_verification_by_default.rb
index 3f070139418..1bd46069f01 100644
--- a/db/migrate/20150915001905_enable_ssl_verification_by_default.rb
+++ b/db/migrate/20150915001905_enable_ssl_verification_by_default.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class EnableSslVerificationByDefault < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     change_column :web_hooks, :enable_ssl_verification, :boolean, default: true
   end
+
+  def down
+    change_column :web_hooks, :enable_ssl_verification, :boolean, default: false
+  end
 end
diff --git a/db/migrate/20150916145038_add_index_for_committed_at_and_id.rb b/db/migrate/20150916145038_add_index_for_committed_at_and_id.rb
index a18ed93cf37..8c0a136753b 100644
--- a/db/migrate/20150916145038_add_index_for_committed_at_and_id.rb
+++ b/db/migrate/20150916145038_add_index_for_committed_at_and_id.rb
@@ -1,6 +1,15 @@
 # rubocop:disable all
 class AddIndexForCommittedAtAndId < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index :ci_commits, [:project_id, :committed_at, :id]
   end
+
+  def down
+    # This one is removed by RemoveRedundantIndexes
+    if index_exists?(:ci_commits, [:project_id, :committed_at, :id])
+      remove_index :ci_commits, column: [:project_id, :committed_at, :id]
+    end
+  end
 end
diff --git a/db/migrate/20150924125150_add_project_id_to_ci_commit.rb b/db/migrate/20150924125150_add_project_id_to_ci_commit.rb
index 905332b7dc7..908768c7608 100644
--- a/db/migrate/20150924125150_add_project_id_to_ci_commit.rb
+++ b/db/migrate/20150924125150_add_project_id_to_ci_commit.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddProjectIdToCiCommit < ActiveRecord::Migration
-  def up
+  DOWNTIME = false
+
+  def change
     add_column :ci_commits, :gl_project_id, :integer
   end
 end
diff --git a/db/migrate/20150930001110_merge_request_error_field.rb b/db/migrate/20150930001110_merge_request_error_field.rb
index 71a8ae3938a..a05169c8e18 100644
--- a/db/migrate/20150930001110_merge_request_error_field.rb
+++ b/db/migrate/20150930001110_merge_request_error_field.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class MergeRequestErrorField < ActiveRecord::Migration
-  def up
+  DOWNTIME = false
+
+  def change
     add_column :merge_requests, :merge_error, :string
   end
 end
diff --git a/db/migrate/20151002122943_migrate_ref_and_tag_to_build.rb b/db/migrate/20151002122943_migrate_ref_and_tag_to_build.rb
index 52217ce5af2..1a8ffe20977 100644
--- a/db/migrate/20151002122943_migrate_ref_and_tag_to_build.rb
+++ b/db/migrate/20151002122943_migrate_ref_and_tag_to_build.rb
@@ -1,7 +1,13 @@
 # rubocop:disable all
 class MigrateRefAndTagToBuild < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     execute('UPDATE ci_builds SET ref=(SELECT ref FROM ci_commits WHERE ci_commits.id = ci_builds.commit_id) WHERE ref IS NULL')
     execute('UPDATE ci_builds SET tag=(SELECT tag FROM ci_commits WHERE ci_commits.id = ci_builds.commit_id) WHERE tag IS NULL')
   end
+
+  def down
+    # no-op
+  end
 end
diff --git a/db/migrate/20151008110232_add_users_lower_username_email_indexes.rb b/db/migrate/20151008110232_add_users_lower_username_email_indexes.rb
index 6080d2a0fcf..f1659e1d7b3 100644
--- a/db/migrate/20151008110232_add_users_lower_username_email_indexes.rb
+++ b/db/migrate/20151008110232_add_users_lower_username_email_indexes.rb
@@ -12,7 +12,7 @@ class AddUsersLowerUsernameEmailIndexes < ActiveRecord::Migration
   def down
     return unless Gitlab::Database.postgresql?
 
-    remove_index :users, :index_on_users_lower_username
-    remove_index :users, :index_on_users_lower_email
+    remove_index :users, name: :index_on_users_lower_username
+    remove_index :users, name: :index_on_users_lower_email
   end
 end
diff --git a/db/migrate/20151008130321_migrate_name_to_description_for_builds.rb b/db/migrate/20151008130321_migrate_name_to_description_for_builds.rb
index 306fa7092ea..8818ef8188a 100644
--- a/db/migrate/20151008130321_migrate_name_to_description_for_builds.rb
+++ b/db/migrate/20151008130321_migrate_name_to_description_for_builds.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class MigrateNameToDescriptionForBuilds < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     execute("UPDATE ci_builds SET type='Ci::Build' WHERE type IS NULL")
   end
+
+  def down
+    # no-op
+  end
 end
diff --git a/db/migrate/20151016195451_add_ci_builds_and_projects_indexes.rb b/db/migrate/20151016195451_add_ci_builds_and_projects_indexes.rb
index 899e004d610..b76548b348f 100644
--- a/db/migrate/20151016195451_add_ci_builds_and_projects_indexes.rb
+++ b/db/migrate/20151016195451_add_ci_builds_and_projects_indexes.rb
@@ -1,10 +1,22 @@
 # rubocop:disable all
 class AddCiBuildsAndProjectsIndexes < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index :ci_projects, :gitlab_id
     add_index :ci_projects, :shared_runners_enabled
 
     add_index :ci_builds, :type
     add_index :ci_builds, :status
   end
+
+  def down
+    # This one is removed by RemoveRedundantIndexes
+    remove_index :ci_projects, column: :gitlab_id if index_exists?(:ci_projects, :gitlab_id)
+    # This one is removed by RemoveRedundantIndexes
+    remove_index :ci_projects, column: :shared_runners_enabled if index_exists?(:ci_projects, :shared_runners_enabled)
+    # This one is removed by RemoveRedundantIndexes
+    remove_index :ci_builds, column: :type if index_exists?(:ci_builds, :type)
+    remove_index :ci_builds, column: :status
+  end
 end
diff --git a/db/migrate/20151020173516_ci_limits_to_mysql.rb b/db/migrate/20151020173516_ci_limits_to_mysql.rb
index 5314611cbcd..1222009d4ba 100644
--- a/db/migrate/20151020173516_ci_limits_to_mysql.rb
+++ b/db/migrate/20151020173516_ci_limits_to_mysql.rb
@@ -1,10 +1,18 @@
 # rubocop:disable all
 class CiLimitsToMysql < ActiveRecord::Migration
-  def change
-    return unless ActiveRecord::Base.configurations[Rails.env]['adapter'] =~ /^mysql/
+  DOWNTIME = false
+
+  def up
+    return unless Gitlab::Database.mysql?
 
     # CI
     change_column :ci_builds, :trace, :text, limit: 1073741823
     change_column :ci_commits, :push_data, :text, limit: 16777215
   end
+
+  def down
+    return unless Gitlab::Database.mysql?
+
+    # no-op, keep the new limit to prevent data loss
+  end
 end
diff --git a/db/migrate/20151103133339_add_shared_runners_setting.rb b/db/migrate/20151103133339_add_shared_runners_setting.rb
index b5b34d4ca61..5afd0f19ebe 100644
--- a/db/migrate/20151103133339_add_shared_runners_setting.rb
+++ b/db/migrate/20151103133339_add_shared_runners_setting.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddSharedRunnersSetting < ActiveRecord::Migration
-  def up
+  DOWNTIME = false
+
+  def change
     add_column :application_settings, :shared_runners_enabled, :boolean, default: true, null: false
   end
 end
diff --git a/db/migrate/20151106000015_add_is_award_to_notes.rb b/db/migrate/20151106000015_add_is_award_to_notes.rb
index b463d939b78..81497c79414 100644
--- a/db/migrate/20151106000015_add_is_award_to_notes.rb
+++ b/db/migrate/20151106000015_add_is_award_to_notes.rb
@@ -1,7 +1,15 @@
 # rubocop:disable all
 class AddIsAwardToNotes < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_column :notes, :is_award, :boolean, default: false, null: false
     add_index :notes, :is_award
   end
+
+  def down
+    remove_column :notes, :is_award
+    # This one is removed in ConvertAwardNoteToEmojiAward
+    remove_index :notes, column: :is_award if index_exists?(:notes, :is_award)
+  end
 end
diff --git a/db/migrate/20151116144118_add_unique_for_lfs_oid_index.rb b/db/migrate/20151116144118_add_unique_for_lfs_oid_index.rb
index 1f192544ea1..b0706846bed 100644
--- a/db/migrate/20151116144118_add_unique_for_lfs_oid_index.rb
+++ b/db/migrate/20151116144118_add_unique_for_lfs_oid_index.rb
@@ -1,8 +1,10 @@
 # rubocop:disable all
 class AddUniqueForLfsOidIndex < ActiveRecord::Migration
+  DOWNTIME = false
+
   def change
-    remove_index :lfs_objects, :oid
-    remove_index :lfs_objects, [:oid, :size]
+    remove_index :lfs_objects, column: :oid
+    remove_index :lfs_objects, column: [:oid, :size]
     add_index :lfs_objects, :oid, unique: true
   end
 end
diff --git a/db/migrate/20151118162244_add_projects_public_index.rb b/db/migrate/20151118162244_add_projects_public_index.rb
index 589f124c21e..61c43c416e9 100644
--- a/db/migrate/20151118162244_add_projects_public_index.rb
+++ b/db/migrate/20151118162244_add_projects_public_index.rb
@@ -1,6 +1,13 @@
 # rubocop:disable all
 class AddProjectsPublicIndex < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index :namespaces, :public
   end
+
+  def down
+    # This one is removed in RemovePublicFromNamespace
+    remove_index :namespaces, :public if index_exists?(:namespaces, :public)
+  end
 end
diff --git a/db/migrate/20151201203948_raise_hook_url_limit.rb b/db/migrate/20151201203948_raise_hook_url_limit.rb
index c490b7ace0f..3b614654e02 100644
--- a/db/migrate/20151201203948_raise_hook_url_limit.rb
+++ b/db/migrate/20151201203948_raise_hook_url_limit.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class RaiseHookUrlLimit < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     change_column :web_hooks, :url, :string, limit: 2000
   end
+
+  def down
+    # no-op, keep the new limit to prevent data loss
+  end
 end
diff --git a/db/migrate/20151210125931_add_index_to_ci_tables.rb b/db/migrate/20151210125931_add_index_to_ci_tables.rb
index d87d335cf6b..7e38a38d751 100644
--- a/db/migrate/20151210125931_add_index_to_ci_tables.rb
+++ b/db/migrate/20151210125931_add_index_to_ci_tables.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class AddIndexToCiTables < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     add_index :ci_builds, :gl_project_id
     add_index :ci_runner_projects, :gl_project_id
     add_index :ci_triggers, :gl_project_id
@@ -10,4 +12,15 @@ class AddIndexToCiTables < ActiveRecord::Migration
     add_index :projects, [:builds_enabled, :shared_runners_enabled]
     add_index :projects, [:ci_id]
   end
+
+  def down
+    remove_index :ci_builds, :gl_project_id if index_exists?(:ci_builds, :gl_project_id)
+    remove_index :ci_runner_projects, :gl_project_id if index_exists?(:ci_runner_projects, :gl_project_id)
+    remove_index :ci_triggers, :gl_project_id if index_exists?(:ci_triggers, :gl_project_id)
+    remove_index :ci_variables, :gl_project_id if index_exists?(:ci_variables, :gl_project_id)
+    remove_index :projects, :runners_token if index_exists?(:projects, :runners_token)
+    remove_index :projects, :builds_enabled if index_exists?(:projects, :builds_enabled)
+    remove_index :projects, [:builds_enabled, :shared_runners_enabled] if index_exists?(:projects, [:builds_enabled, :shared_runners_enabled])
+    remove_index :projects, [:ci_id] if index_exists?(:projects, [:ci_id])
+  end
 end
diff --git a/db/migrate/20151210125932_drop_null_for_ci_tables.rb b/db/migrate/20151210125932_drop_null_for_ci_tables.rb
index e1a0a964589..6b6b56b0a54 100644
--- a/db/migrate/20151210125932_drop_null_for_ci_tables.rb
+++ b/db/migrate/20151210125932_drop_null_for_ci_tables.rb
@@ -1,8 +1,10 @@
 # rubocop:disable all
 class DropNullForCiTables < ActiveRecord::Migration
+  DOWNTIME = false
+
   def change
-    remove_index :ci_variables, :project_id
-    remove_index :ci_runner_projects, :project_id
+    remove_index :ci_variables, column:  :project_id
+    remove_index :ci_runner_projects, column:  :project_id
     change_column_null :ci_triggers, :project_id, true
     change_column_null :ci_variables, :project_id, true
     change_column_null :ci_runner_projects, :project_id, true
diff --git a/db/migrate/20151229112614_influxdb_remote_database_setting.rb b/db/migrate/20151229112614_influxdb_remote_database_setting.rb
index d2ac906ead3..57abe3b1ea4 100644
--- a/db/migrate/20151229112614_influxdb_remote_database_setting.rb
+++ b/db/migrate/20151229112614_influxdb_remote_database_setting.rb
@@ -1,6 +1,8 @@
 # rubocop:disable all
 class InfluxdbRemoteDatabaseSetting < ActiveRecord::Migration
+  DOWNTIME = false
+
   def change
-    remove_column :application_settings, :metrics_database
+    remove_column :application_settings, :metrics_database, :string
   end
 end
diff --git a/db/migrate/20160128233227_change_lfs_objects_size_column.rb b/db/migrate/20160128233227_change_lfs_objects_size_column.rb
index 645c0cdb192..b7f61484eca 100644
--- a/db/migrate/20160128233227_change_lfs_objects_size_column.rb
+++ b/db/migrate/20160128233227_change_lfs_objects_size_column.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class ChangeLfsObjectsSizeColumn < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     change_column :lfs_objects, :size, :integer, limit: 8
   end
+
+  def down
+    # no-op, keep the new limit to prevent data loss
+  end
 end
diff --git a/db/migrate/20160320204112_index_namespaces_on_visibility_level.rb b/db/migrate/20160320204112_index_namespaces_on_visibility_level.rb
index 07ae7c95477..1452aa65ada 100644
--- a/db/migrate/20160320204112_index_namespaces_on_visibility_level.rb
+++ b/db/migrate/20160320204112_index_namespaces_on_visibility_level.rb
@@ -1,8 +1,16 @@
 # rubocop:disable all
 class IndexNamespacesOnVisibilityLevel < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     unless index_exists?(:namespaces, :visibility_level)
       add_index :namespaces, :visibility_level
     end
   end
+
+  def down
+    if index_exists?(:namespaces, :visibility_level)
+      add_index :namespaces, :visibility_level
+    end
+  end
 end
diff --git a/db/migrate/20160412173417_update_ci_commit.rb b/db/migrate/20160412173417_update_ci_commit.rb
index 858faeb060e..c0da9f1087b 100644
--- a/db/migrate/20160412173417_update_ci_commit.rb
+++ b/db/migrate/20160412173417_update_ci_commit.rb
@@ -2,10 +2,16 @@
 class UpdateCiCommit < ActiveRecord::Migration
   # This migration can be run online, but needs to be executed for the second time after restarting Unicorn workers
   # Otherwise Offline migration should be used.
-  def change
+  DOWNTIME = false
+
+  def up
     execute("UPDATE ci_commits SET status=#{status}, ref=#{ref}, tag=#{tag} WHERE status IS NULL")
   end
 
+  def down
+    # no-op
+  end
+
   private
 
   def status
diff --git a/db/migrate/20160508221410_set_type_on_legacy_diff_notes.rb b/db/migrate/20160508221410_set_type_on_legacy_diff_notes.rb
index 6dd958ff4a0..2b4e4d398dd 100644
--- a/db/migrate/20160508221410_set_type_on_legacy_diff_notes.rb
+++ b/db/migrate/20160508221410_set_type_on_legacy_diff_notes.rb
@@ -1,6 +1,12 @@
 # rubocop:disable all
 class SetTypeOnLegacyDiffNotes < ActiveRecord::Migration
-  def change
+  DOWNTIME = false
+
+  def up
     execute "UPDATE notes SET type = 'LegacyDiffNote' WHERE line_code IS NOT NULL"
   end
+
+  def down
+    # no-op
+  end
 end
diff --git a/db/migrate/20160525205328_remove_main_language_from_projects.rb b/db/migrate/20160525205328_remove_main_language_from_projects.rb
index dc4ceacddb1..1af143991ef 100644
--- a/db/migrate/20160525205328_remove_main_language_from_projects.rb
+++ b/db/migrate/20160525205328_remove_main_language_from_projects.rb
@@ -1,22 +1,10 @@
 # rubocop:disable all
-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 class RemoveMainLanguageFromProjects < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
-  # When using the methods "add_concurrent_index" or "add_column_with_default"
-  # you must disable the use of transactions as these methods can not run in an
-  # existing transaction. When using "add_concurrent_index" make sure that this
-  # method is the _only_ method called in the migration, any other changes
-  # should go in a separate migration. This ensures that upon failure _only_ the
-  # index creation fails and can be retried or reverted easily.
-  #
-  # To disable transactions uncomment the following line and remove these
-  # comments:
-  # disable_ddl_transaction!
+  DOWNTIME = false
 
   def change
-    remove_column :projects, :main_language
+    remove_column :projects, :main_language, :string
   end
 end
diff --git a/db/migrate/20160528043124_add_users_state_index.rb b/db/migrate/20160528043124_add_users_state_index.rb
index 6419d2ae71d..53b009ff0e7 100644
--- a/db/migrate/20160528043124_add_users_state_index.rb
+++ b/db/migrate/20160528043124_add_users_state_index.rb
@@ -1,10 +1,15 @@
 # rubocop:disable all
 class AddUsersStateIndex < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
-
   disable_ddl_transaction!
 
-  def change
+  DOWNTIME = false
+
+  def up
     add_concurrent_index :users, :state
   end
+
+  def down
+    remove_index :users, :state
+  end
 end
diff --git a/db/migrate/20160603182247_add_index_to_notification_settings.rb b/db/migrate/20160603182247_add_index_to_notification_settings.rb
index f6ae26d555f..6463e346582 100644
--- a/db/migrate/20160603182247_add_index_to_notification_settings.rb
+++ b/db/migrate/20160603182247_add_index_to_notification_settings.rb
@@ -1,10 +1,15 @@
 # rubocop:disable all
 class AddIndexToNotificationSettings < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
-
   disable_ddl_transaction!
 
-  def change
+  DOWNTIME = false
+
+  def up
     add_concurrent_index :notification_settings, [:user_id, :source_id, :source_type], { unique: true, name: "index_notifications_on_user_id_and_source_id_and_source_type" }
   end
+
+  def down
+    remove_index :notification_settings, column: [:user_id, :source_id, :source_type], unique: true, name: "index_notifications_on_user_id_and_source_id_and_source_type"
+  end
 end
diff --git a/db/migrate/20160610140403_remove_notification_setting_not_null_constraints.rb b/db/migrate/20160610140403_remove_notification_setting_not_null_constraints.rb
index 259abb08e47..09463dae3b5 100644
--- a/db/migrate/20160610140403_remove_notification_setting_not_null_constraints.rb
+++ b/db/migrate/20160610140403_remove_notification_setting_not_null_constraints.rb
@@ -1,11 +1,14 @@
 class RemoveNotificationSettingNotNullConstraints < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
   def up
     change_column :notification_settings, :source_type, :string, null: true
     change_column :notification_settings, :source_id, :integer, null: true
   end
 
   def down
-    change_column :notification_settings, :source_type, :string, null: false
-    change_column :notification_settings, :source_id, :integer, null: false
+    # no-op since the data would prevent the change of the null constraint
   end
 end
diff --git a/db/migrate/20160703180340_add_index_on_award_emoji_user_and_name.rb b/db/migrate/20160703180340_add_index_on_award_emoji_user_and_name.rb
index 0c25f87dfb4..1670fe19c5e 100644
--- a/db/migrate/20160703180340_add_index_on_award_emoji_user_and_name.rb
+++ b/db/migrate/20160703180340_add_index_on_award_emoji_user_and_name.rb
@@ -5,7 +5,13 @@ class AddIndexOnAwardEmojiUserAndName < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
   disable_ddl_transaction!
 
-  def change
+  DOWNTIME = false
+
+  def up
     add_concurrent_index(:award_emoji, [:user_id, :name])
   end
+
+  def down
+    remove_index :award_emoji, [:user_id, :name]
+  end
 end
diff --git a/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb b/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb
index 12e11bc3fbe..85bc7d867c2 100644
--- a/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb
+++ b/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb
@@ -1,6 +1,3 @@
-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 # rubocop:disable RemoveIndex
 class MergeRequestDiffRemoveUniq < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
@@ -25,9 +22,7 @@ class MergeRequestDiffRemoveUniq < ActiveRecord::Migration
   end
 
   def down
-    unless index_exists?(:merge_request_diffs, :merge_request_id)
-      add_concurrent_index(:merge_request_diffs, :merge_request_id, unique: true)
-    end
+    # no-op since the data would prevent the creation of a unique index
   end
 
   def constraint_exists?(name)
diff --git a/db/migrate/20160802010328_remove_builds_enable_index_on_projects.rb b/db/migrate/20160802010328_remove_builds_enable_index_on_projects.rb
index 6d7733762c8..7d382edab38 100644
--- a/db/migrate/20160802010328_remove_builds_enable_index_on_projects.rb
+++ b/db/migrate/20160802010328_remove_builds_enable_index_on_projects.rb
@@ -1,10 +1,15 @@
 # rubocop:disable RemoveIndex
+# rubocop:disable AddIndex
 class RemoveBuildsEnableIndexOnProjects < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
   DOWNTIME = false
 
-  def change
-    remove_index :projects, column: :builds_enabled if index_exists?(:projects, :builds_enabled)
+  def up
+    remove_index :projects, :builds_enabled if index_exists?(:projects, :builds_enabled)
+  end
+
+  def down
+    add_index :projects, :builds_enabled unless index_exists?(:projects, :builds_enabled)
   end
 end
diff --git a/db/migrate/20160808085602_add_index_for_build_token.rb b/db/migrate/20160808085602_add_index_for_build_token.rb
index 0446b2f2e15..d6771688dae 100644
--- a/db/migrate/20160808085602_add_index_for_build_token.rb
+++ b/db/migrate/20160808085602_add_index_for_build_token.rb
@@ -2,7 +2,6 @@
 class AddIndexForBuildToken < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
-  # Set this constant to true if this migration requires downtime.
   DOWNTIME = false
 
   disable_ddl_transaction!
@@ -12,6 +11,6 @@ class AddIndexForBuildToken < ActiveRecord::Migration
   end
 
   def down
-    remove_index :ci_builds, :token, unique: true if index_exists? :ci_builds, :token, unique: true
+    remove_index :ci_builds, :token if index_exists? :ci_builds, :token, unique: true
   end
 end
diff --git a/db/migrate/20160823081327_change_merge_error_to_text.rb b/db/migrate/20160823081327_change_merge_error_to_text.rb
index 7920389cd83..be244993de5 100644
--- a/db/migrate/20160823081327_change_merge_error_to_text.rb
+++ b/db/migrate/20160823081327_change_merge_error_to_text.rb
@@ -4,7 +4,11 @@ class ChangeMergeErrorToText < ActiveRecord::Migration
   DOWNTIME = true
   DOWNTIME_REASON = 'This migration requires downtime because it alters a column from varchar(255) to text.'
 
-  def change
+  def up
     change_column :merge_requests, :merge_error, :text, limit: 65535
   end
+
+  def down
+    change_column :merge_requests, :merge_error, :string
+  end
 end
diff --git a/db/migrate/20160824103857_drop_unused_ci_tables.rb b/db/migrate/20160824103857_drop_unused_ci_tables.rb
index 65cf46308d9..33bb56208d2 100644
--- a/db/migrate/20160824103857_drop_unused_ci_tables.rb
+++ b/db/migrate/20160824103857_drop_unused_ci_tables.rb
@@ -4,8 +4,27 @@ class DropUnusedCiTables < ActiveRecord::Migration
   # Set this constant to true if this migration requires downtime.
   DOWNTIME = false
 
-  def change
+  def up
     drop_table(:ci_services)
     drop_table(:ci_web_hooks)
   end
+
+  def down
+    create_table "ci_web_hooks", force: true do |t|
+      t.string   "url",        null: false
+      t.integer  "project_id", null: false
+      t.datetime "created_at"
+      t.datetime "updated_at"
+    end
+
+    create_table "ci_services", force: true do |t|
+      t.string   "type"
+      t.string   "title"
+      t.integer  "project_id",                 null: false
+      t.datetime "created_at"
+      t.datetime "updated_at"
+      t.boolean  "active",     default: false, null: false
+      t.text     "properties"
+    end
+  end
 end
diff --git a/db/migrate/20160919144305_add_type_to_labels.rb b/db/migrate/20160919144305_add_type_to_labels.rb
index 66172bda6ff..96d72d24184 100644
--- a/db/migrate/20160919144305_add_type_to_labels.rb
+++ b/db/migrate/20160919144305_add_type_to_labels.rb
@@ -4,11 +4,15 @@ class AddTypeToLabels < ActiveRecord::Migration
   DOWNTIME = true
   DOWNTIME_REASON = 'Labels will not work as expected until this migration is complete.'
 
-  def change
+  def up
     add_column :labels, :type, :string
 
     update_column_in_batches(:labels, :type, 'ProjectLabel') do |table, query|
       query.where(table[:project_id].not_eq(nil))
     end
   end
+
+  def down
+    remove_column :labels, :type
+  end
 end