Remove dead MySQL code

None of this code can be reached any more, so it can all be removed

Gemfile

@@ -16,7 +16,6 @@ gem 'sprockets', '~> 3.7.0'
 gem 'default_value_for', '~> 3.2.0'
 # Supported DBs
-gem 'mysql2', '~> 0.4.10', group: :mysql
 gem 'pg', '~> 1.1', group: :postgres
 gem 'rugged', '~> 0.28'
@@ -298,7 +297,6 @@ gem 'batch-loader', '~> 1.4.0'
 # Perf bar
 gem 'peek', '~> 1.0.1'
 gem 'peek-gc', '~> 0.0.2'
-gem 'peek-mysql2', '~> 1.2.0', group: :mysql
 gem 'peek-pg', '~> 1.3.0', group: :postgres
 gem 'peek-rblineprof', '~> 0.2.0'

Gemfile.lock

@@ -536,7 +536,6 @@ GEM
     mustermann (1.0.3)
     mustermann-grape (1.0.0)
       mustermann (~> 1.0.0)
-    mysql2 (0.4.10)
     nakayoshi_fork (0.0.4)
     net-ldap (0.16.0)
     net-ssh (5.2.0)
@@ -644,11 +643,6 @@ GEM
       railties (>= 4.0.0)
     peek-gc (0.0.2)
       peek
-    peek-mysql2 (1.2.0)
-      concurrent-ruby
-      concurrent-ruby-ext
-      mysql2
-      peek
     peek-pg (1.3.0)
       concurrent-ruby
       concurrent-ruby-ext
@@ -1163,7 +1157,6 @@ DEPENDENCIES
   mimemagic (~> 0.3.2)
   mini_magick
   minitest (~> 5.11.0)
-  mysql2 (~> 0.4.10)
   nakayoshi_fork (~> 0.0.4)
   net-ldap
   net-ssh (~> 5.2)
@@ -1191,7 +1184,6 @@ DEPENDENCIES
   org-ruby (~> 0.9.12)
   peek (~> 1.0.1)
   peek-gc (~> 0.0.2)
-  peek-mysql2 (~> 1.2.0)
   peek-pg (~> 1.3.0)
   peek-rblineprof (~> 0.2.0)
   pg (~> 1.1)

app/models/ci/pipeline.rb

@@ -236,8 +236,6 @@ module Ci
       if limit
         ids = relation.limit(limit).select(:id)
-        # MySQL does not support limit in subquery
-        ids = ids.pluck(:id) if Gitlab::Database.mysql?
         relation = relation.where(id: ids)
       end

app/models/concerns/case_sensitivity.rb

@@ -40,14 +40,10 @@ module CaseSensitivity
     end
     def lower_value(value)
-      return value if Gitlab::Database.mysql?
-
       Arel::Nodes::NamedFunction.new('LOWER', [Arel::Nodes.build_quoted(value)])
     end
     def lower_column(column)
-      return column if Gitlab::Database.mysql?
-
       column.lower
     end
   end

app/models/concerns/routable.rb

@@ -33,29 +33,12 @@ module Routable
     #
     # Returns a single object, or nil.
     def find_by_full_path(path, follow_redirects: false)
-      # On MySQL we want to ensure the ORDER BY uses a case-sensitive match so
-      # any literal matches come first, for this we have to use "BINARY".
-      # Without this there's still no guarantee in what order MySQL will return
-      # rows.
-      #
-      # Why do we do this?
-      #
-      # Even though we have Rails validation on Route for unique paths
-      # (case-insensitive), there are old projects in our DB (and possibly
-      # clients' DBs) that have the same path with different cases.
-      # See https://gitlab.com/gitlab-org/gitlab-ce/issues/18603. Also note that
-      # our unique index is case-sensitive in Postgres.
-      binary = Gitlab::Database.mysql? ? 'BINARY' : ''
-      order_sql = Arel.sql("(CASE WHEN #{binary} routes.path = #{connection.quote(path)} THEN 0 ELSE 1 END)")
+      order_sql = Arel.sql("(CASE WHEN routes.path = #{connection.quote(path)} THEN 0 ELSE 1 END)")
       found = where_full_path_in([path]).reorder(order_sql).take
       return found if found
       if follow_redirects
-        if Gitlab::Database.postgresql?
-          joins(:redirect_routes).find_by("LOWER(redirect_routes.path) = LOWER(?)", path)
-        else
-          joins(:redirect_routes).find_by(redirect_routes: { path: path })
-        end
+        joins(:redirect_routes).find_by("LOWER(redirect_routes.path) = LOWER(?)", path)
       end
     end
@@ -67,27 +50,13 @@ module Routable
     #
     # Returns an ActiveRecord::Relation.
     def where_full_path_in(paths)
-      wheres = []
-      cast_lower = Gitlab::Database.postgresql?
-      paths.each do |path|
-        path = connection.quote(path)
-
-        where =
-          if cast_lower
-            "(LOWER(routes.path) = LOWER(#{path}))"
-          else
-            "(routes.path = #{path})"
-          end
-
-        wheres << where
+      return none if paths.empty?
+      wheres = paths.map do |path|
+        "(LOWER(routes.path) = LOWER(#{connection.quote(path)}))"
       end
-      if wheres.empty?
-        none
-      else
-        joins(:route).where(wheres.join(' OR '))
-      end
+      joins(:route).where(wheres.join(' OR '))
     end
   end

app/models/deployment.rb

@@ -128,17 +128,8 @@ class Deployment < ApplicationRecord
       merge_requests = merge_requests.where("merge_request_metrics.merged_at >= ?", previous_deployment.finished_at)
     end
-    # Need to use `map` instead of `select` because MySQL doesn't allow `SELECT`ing from the same table
-    # that we're updating.
-    merge_request_ids =
-      if Gitlab::Database.postgresql?
-        merge_requests.select(:id)
-      elsif Gitlab::Database.mysql?
-        merge_requests.map(&:id)
-      end
-
     MergeRequest::Metrics
-      .where(merge_request_id: merge_request_ids, first_deployed_to_production_at: nil)
+      .where(merge_request_id: merge_requests.select(:id), first_deployed_to_production_at: nil)
       .update_all(first_deployed_to_production_at: finished_at)
   end

app/uploaders/records_uploads.rb

@@ -23,15 +23,7 @@ module RecordsUploads
       return unless model
       return unless file && file.exists?
-      # MySQL InnoDB may encounter a deadlock if a deletion and an
-      # insert is in the same transaction due to its next-key locking
-      # algorithm, so we need to skip the transaction.
-      # https://gitlab.com/gitlab-org/gitlab-ce/issues/55161#note_131556351
-      if Gitlab::Database.mysql?
-        readd_upload
-      else
-        Upload.transaction { readd_upload }
-      end
+      Upload.transaction { readd_upload }
     end
     def readd_upload

config/application.rb

@@ -22,11 +22,6 @@ module Gitlab
     require_dependency Rails.root.join('lib/gitlab/middleware/read_only')
     require_dependency Rails.root.join('lib/gitlab/middleware/basic_health_check')
-    # This needs to be loaded before DB connection is made
-    # to make sure that all connections have NO_ZERO_DATE
-    # setting disabled
-    require_dependency Rails.root.join('lib/mysql_zero_date')
-
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.

config/database.yml.mysql

-#
-# PRODUCTION
-#
-production:
-  adapter: mysql2
-  encoding: utf8
-  collation: utf8_general_ci
-  reconnect: false
-  database: gitlabhq_production
-  pool: 10
-  username: git
-  password: "secure password"
-  host: localhost
-  # socket: /tmp/mysql.sock
-
-#
-# Development specific
-#
-development:
-  adapter: mysql2
-  encoding: utf8
-  collation: utf8_general_ci
-  reconnect: false
-  database: gitlabhq_development
-  pool: 5
-  username: root
-  password: "secure password"
-  host: localhost
-  # socket: /tmp/mysql.sock
-
-#
-# Staging specific
-#
-staging:
-  adapter: mysql2
-  encoding: utf8
-  collation: utf8_general_ci
-  reconnect: false
-  database: gitlabhq_staging
-  pool: 10
-  username: git
-  password: "secure password"
-  host: localhost
-  # socket: /tmp/mysql.sock
-
-# Warning: The database defined as "test" will be erased and
-# re-generated from your development database when you run "rake".
-# Do not set this db to the same as development or production.
-test: &test
-  adapter: mysql2
-  encoding: utf8mb4
-  collation: utf8mb4_general_ci
-  reconnect: false
-  database: gitlabhq_test
-  pool: 5
-  username: root
-  password:
-  host: localhost
-  # socket: /tmp/mysql.sock
-  prepared_statements: false

config/initializers/active_record_data_types.rb

 # ActiveRecord custom data type for storing datetimes with timezone information.
 # See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11229
-if Gitlab::Database.postgresql?
-  require 'active_record/connection_adapters/postgresql_adapter'
-  module ActiveRecord::ConnectionAdapters::PostgreSQL::OID
-    # Add the class `DateTimeWithTimeZone` so we can map `timestamptz` to it.
-    class DateTimeWithTimeZone < DateTime
-      def type
-        :datetime_with_timezone
-      end
+require 'active_record/connection_adapters/postgresql_adapter'
+module ActiveRecord::ConnectionAdapters::PostgreSQL::OID
+  # Add the class `DateTimeWithTimeZone` so we can map `timestamptz` to it.
+  class DateTimeWithTimeZone < DateTime
+    def type
+      :datetime_with_timezone
     end
   end
-  module RegisterDateTimeWithTimeZone
-    # Run original `initialize_type_map` and then register `timestamptz` as a
-    # `DateTimeWithTimeZone`.
-    #
-    # Apparently it does not matter that the original `initialize_type_map`
-    # aliases `timestamptz` to `timestamp`.
-    #
-    # When schema dumping, `timestamptz` columns will be output as
-    # `t.datetime_with_timezone`.
-    def initialize_type_map(mapping = type_map)
-      super mapping
-
-      mapping.register_type 'timestamptz' do |_, _, sql_type|
-        precision = extract_precision(sql_type)
-        ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::OID::DateTimeWithTimeZone.new(precision: precision)
-      end
-    end
-  end
-
-  class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
-    prepend RegisterDateTimeWithTimeZone
-
-    # Add column type `datetime_with_timezone` so we can do this in
-    # migrations:
-    #
-    #   add_column(:users, :datetime_with_timezone)
-    #
-    NATIVE_DATABASE_TYPES[:datetime_with_timezone] = { name: 'timestamptz' }
-  end
-elsif Gitlab::Database.mysql?
-  require 'active_record/connection_adapters/mysql2_adapter'
-
-  module RegisterDateTimeWithTimeZone
-    # Run original `initialize_type_map` and then register `timestamp` as a
-    # `MysqlDateTimeWithTimeZone`.
-    #
-    # When schema dumping, `timestamp` columns will be output as
-    # `t.datetime_with_timezone`.
-    def initialize_type_map(mapping = type_map)
-      super mapping
-
-      mapping.register_type(/timestamp/i) do |sql_type|
-        precision = extract_precision(sql_type)
-        ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlDateTimeWithTimeZone.new(precision: precision)
-      end
+end
+module RegisterDateTimeWithTimeZone
+  # Run original `initialize_type_map` and then register `timestamptz` as a
+  # `DateTimeWithTimeZone`.
+  #
+  # Apparently it does not matter that the original `initialize_type_map`
+  # aliases `timestamptz` to `timestamp`.
+  #
+  # When schema dumping, `timestamptz` columns will be output as
+  # `t.datetime_with_timezone`.
+  def initialize_type_map(mapping = type_map)
+    super mapping
+
+    mapping.register_type 'timestamptz' do |_, _, sql_type|
+      precision = extract_precision(sql_type)
+      ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::OID::DateTimeWithTimeZone.new(precision: precision)
     end
   end
-  class ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter
-    prepend RegisterDateTimeWithTimeZone
-
-    # Add the class `DateTimeWithTimeZone` so we can map `timestamp` to it.
-    class MysqlDateTimeWithTimeZone < ActiveRecord::Type::DateTime
-      def type
-        :datetime_with_timezone
-      end
-    end
-    # Add column type `datetime_with_timezone` so we can do this in
-    # migrations:
-    #
-    #   add_column(:users, :datetime_with_timezone)
-    #
-    NATIVE_DATABASE_TYPES[:datetime_with_timezone] = { name: 'timestamp' }
-  end
+end
+class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
+  prepend RegisterDateTimeWithTimeZone
+  # Add column type `datetime_with_timezone` so we can do this in
+  # migrations:
+  #
+  #   add_column(:users, :datetime_with_timezone)
+  #
+  NATIVE_DATABASE_TYPES[:datetime_with_timezone] = { name: 'timestamptz' }
 end
 # Ensure `datetime_with_timezone` columns are correctly written to schema.rb

config/initializers/active_record_mysql_timestamp.rb

-# Make sure that MySQL won't try to use CURRENT_TIMESTAMP when the timestamp
-# column is NOT NULL. See https://gitlab.com/gitlab-org/gitlab-ce/issues/36405
-# And also: https://bugs.mysql.com/bug.php?id=75098
-# This patch was based on:
-# https://github.com/rails/rails/blob/15ef55efb591e5379486ccf53dd3e13f416564f6/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb#L34-L36
-
-if Gitlab::Database.mysql?
-  require 'active_record/connection_adapters/abstract/schema_creation'
-
-  module MySQLTimestampFix
-    def add_column_options!(sql, options)
-      # By default, TIMESTAMP columns are NOT NULL, cannot contain NULL values,
-      # and assigning NULL assigns the current timestamp. To permit a TIMESTAMP
-      # column to contain NULL, explicitly declare it with the NULL attribute.
-      # See http://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html
-      if sql.end_with?('timestamp') && !options[:primary_key]
-        if options[:null] != false
-          sql << ' NULL'
-        elsif options[:column].default.nil?
-          sql << ' DEFAULT 0'
-        end
-      end
-
-      super
-    end
-  end
-
-  ActiveRecord::ConnectionAdapters::AbstractAdapter::SchemaCreation
-    .prepend(MySQLTimestampFix)
-end

config/initializers/ar_mysql_jsonb_support.rb

-# frozen_string_literal: true
-
-require 'active_record/connection_adapters/abstract_mysql_adapter'
-require 'active_record/connection_adapters/mysql/schema_definitions'
-
-# MySQL (5.6) and MariaDB (10.1) are currently supported versions within GitLab,
-# Since they do not support native `json` datatype we force to emulate it as `text`
-
-if Gitlab::Database.mysql?
-  module ActiveRecord
-    module ConnectionAdapters
-      class AbstractMysqlAdapter
-        JSON_DATASIZE = 1.megabyte
-
-        NATIVE_DATABASE_TYPES.merge!(
-          json: { name: "text", limit: JSON_DATASIZE },
-          jsonb: { name: "text", limit: JSON_DATASIZE }
-        )
-      end
-
-      module MySQL
-        module ColumnMethods
-          # We add `jsonb` helper, as `json` is already defined for `MySQL` since Rails 5
-          def jsonb(*args, **options)
-            args.each { |name| column(name, :json, options) }
-          end
-        end
-      end
-    end
-  end
-end

config/initializers/ar_native_database_types.rb

-require 'active_record/connection_adapters/abstract_mysql_adapter'
-
-module ActiveRecord
-  module ConnectionAdapters
-    class AbstractMysqlAdapter
-      NATIVE_DATABASE_TYPES.merge!(
-        bigserial: { name: 'bigint(20) auto_increment PRIMARY KEY' },
-        serial: { name: 'int auto_increment PRIMARY KEY' }
-      )
-    end
-  end
-end

config/initializers/connection_fix.rb

-# from http://gist.github.com/238999
-#
-# If your workers are inactive for a long period of time, they'll lose
-# their MySQL connection.
-#
-# This hack ensures we re-connect whenever a connection is
-# lost. Because, really. why not?
-#
-# Stick this in RAILS_ROOT/config/initializers/connection_fix.rb (or somewhere similar)
-#
-# From:
-#   http://coderrr.wordpress.com/2009/01/08/activerecord-threading-issues-and-resolutions/
-
-if defined?(ActiveRecord::ConnectionAdapters::Mysql2Adapter)
-  module ActiveRecord::ConnectionAdapters
-    class Mysql2Adapter
-      alias_method :execute_without_retry, :execute
-
-      def execute(*args)
-        execute_without_retry(*args)
-      rescue ActiveRecord::StatementInvalid => e
-        if e.message =~ /server has gone away/i
-          warn "Lost connection to MySQL server during query"
-          reconnect!
-          retry
-        else
-          raise e
-        end
-      end
-    end
-  end
-end

config/initializers/mysql_ignore_postgresql_options.rb

-# This patches ActiveRecord so indexes created using the MySQL adapter ignore
-# any PostgreSQL specific options (e.g. `using: :gin`).
-#
-# These patches do the following for MySQL:
-#
-# 1. Indexes created using the :opclasses option are ignored (as they serve no
-#    purpose on MySQL).
-# 2. When creating an index with `using: :gin` the `using` option is discarded
-#    as :gin is not a valid value for MySQL.
-# 3. The `:opclasses` option is stripped from add_index_options in case it's
-#    used anywhere other than in the add_index methods.
-
-if defined?(ActiveRecord::ConnectionAdapters::Mysql2Adapter)
-  module ActiveRecord
-    module ConnectionAdapters
-      class Mysql2Adapter < AbstractMysqlAdapter
-        alias_method :__gitlab_add_index, :add_index
-        alias_method :__gitlab_add_index_options, :add_index_options
-
-        def add_index(table_name, column_name, options = {})
-          unless options[:opclasses]
-            __gitlab_add_index(table_name, column_name, options)
-          end
-        end
-
-        def add_index_options(table_name, column_name, options = {})
-          if options[:using] && options[:using] == :gin
-            options = options.dup
-            options.delete(:using)
-          end
-
-          if options[:opclasses]
-            options = options.dup
-            options.delete(:opclasses)
-          end
-
-          __gitlab_add_index_options(table_name, column_name, options)
-        end
-      end
-    end
-  end
-end

config/initializers/mysql_set_length_for_binary_indexes.rb

-# This patches ActiveRecord so indexes for binary columns created using the
-# MySQL adapter apply a length of 20. Otherwise MySQL can't create an index on
-# binary columns.
-
-module MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema
-  # This method is used in Rails 5 schema loading as t.index
-  def index(column_names, options = {})
-    # Ignore indexes that use opclasses,
-    # also see config/initializers/mysql_ignore_postgresql_options.rb
-    if options[:opclasses]
-      warn "WARNING: index on columns #{column_names} uses unsupported option, skipping."
-      return
-    end
-
-    options[:length] ||= {}
-    Array(column_names).each do |column_name|
-      column = columns.find { |c| c.name == column_name }
-
-      if column&.type == :binary
-        options[:length][column_name] = 20
-      end
-    end
-
-    super(column_names, options)
-  end
-end
-
-if defined?(ActiveRecord::ConnectionAdapters::MySQL::TableDefinition)
-  ActiveRecord::ConnectionAdapters::MySQL::TableDefinition.send(:prepend, MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema)
-end

config/initializers/peek.rb

@@ -2,11 +2,7 @@ Rails.application.config.peek.adapter = :redis, { client: ::Redis.new(Gitlab::Re
 Peek.into Peek::Views::Host
-if Gitlab::Database.mysql?
-  require 'peek-mysql2'
-  PEEK_DB_CLIENT = ::Mysql2::Client
-  PEEK_DB_VIEW = Peek::Views::Mysql2
-elsif Gitlab::Database.postgresql?
+if Gitlab::Database.postgresql?
   require 'peek-pg'
   PEEK_DB_CLIENT = ::PG::Connection
   PEEK_DB_VIEW = Peek::Views::PG

db/migrate/20180206200543_reset_events_primary_key_sequence.rb

@@ -12,24 +12,10 @@ class ResetEventsPrimaryKeySequence < ActiveRecord::Migration[4.2]
   end
   def up
-    if Gitlab::Database.postgresql?
-      reset_primary_key_for_postgresql
-    else
-      reset_primary_key_for_mysql
-    end
+    reset_pk_sequence!(Event.table_name)
   end
   def down
     # No-op
   end
-
-  def reset_primary_key_for_postgresql
-    reset_pk_sequence!(Event.table_name)
-  end
-
-  def reset_primary_key_for_mysql
-    amount = Event.pluck('COALESCE(MAX(id), 1)').first
-
-    execute "ALTER TABLE #{Event.table_name} AUTO_INCREMENT = #{amount}"
-  end
 end

db/migrate/20180403035759_create_project_ci_cd_settings.rb

@@ -30,12 +30,6 @@ class CreateProjectCiCdSettings < ActiveRecord::Migration[4.2]
   end
   def add_foreign_key_with_retry
-    if Gitlab::Database.mysql?
-      # When using MySQL we don't support online upgrades, thus projects can't
-      # be deleted while we are running this migration.
-      return add_project_id_foreign_key
-    end
-
     # Between the initial INSERT and the addition of the foreign key some
     # projects may have been removed, leaving orphaned rows in our new settings
     # table.

db/migrate/20180406204716_add_limits_ci_build_trace_chunks_raw_data_for_mysql.rb

-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-require Rails.root.join('db/migrate/limits_ci_build_trace_chunks_raw_data_for_mysql')
-
-class AddLimitsCiBuildTraceChunksRawDataForMysql < ActiveRecord::Migration[4.2]
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  def up
-    LimitsCiBuildTraceChunksRawDataForMysql.new.up
-  end
-end