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'
@@ -310,7 +309,6 @@ 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

@@ -565,7 +565,6 @@ GEM
     mustermann (1.0.3)
     mustermann-grape (1.0.0)
       mustermann (~> 1.0.0)
-    mysql2 (0.4.10)
     nakayoshi_fork (0.0.4)
     net-dns (0.9.0)
     net-ldap (0.16.0)
@@ -675,11 +674,6 @@ 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
@@ -1203,7 +1197,6 @@ DEPENDENCIES
   mimemagic (~> 0.3.2)
   mini_magick
   minitest (~> 5.11.0)
-  mysql2 (~> 0.4.10)
   nakayoshi_fork (~> 0.0.4)
   net-dns (~> 0.9.0)
   net-ldap
@@ -1233,7 +1226,6 @@ 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?
+      return none if paths.empty?
 
-      paths.each do |path|
-        path = connection.quote(path)
-
-        where =
-          if cast_lower
-            "(LOWER(routes.path) = LOWER(#{path}))"
-          else
-            "(routes.path = #{path})"
-          end
-
-        wheres << where
+      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'
+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
+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
+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
+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::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
+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: 'timestamp' }
-  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: '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

db/migrate/20180521171529_increase_mysql_text_limit_for_gpg_keys.rb

-require_relative 'gpg_keys_limits_to_mysql'

db/migrate/20180831164904_fix_prometheus_metric_query_limits.rb

-# frozen_string_literal: true
-
-# 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/prometheus_metrics_limits_to_mysql')
-
-class FixPrometheusMetricQueryLimits < ActiveRecord::Migration[4.2]
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  def up
-    PrometheusMetricsLimitsToMysql.new.up
-  end
-
-  def down
-    # no-op
-  end
-end

db/migrate/20181030154446_add_missing_indexes_for_foreign_keys.rb

@@ -34,10 +34,6 @@ class AddMissingIndexesForForeignKeys < ActiveRecord::Migration[4.2]
   end
 
   def down
-    # MySQL requires index for FK,
-    # thus removal of indexes does fail
-    return if Gitlab::Database.mysql?
-
     remove_concurrent_index(:application_settings, :usage_stats_set_by_user_id)
     remove_concurrent_index(:ci_pipeline_schedules, :owner_id)
     remove_concurrent_index(:ci_trigger_requests, :trigger_id)

db/migrate/gpg_keys_limits_to_mysql.rb

-class IncreaseMysqlTextLimitForGpgKeys < ActiveRecord::Migration[4.2]
-  # Set this constant to true if this migration requires downtime.
-  DOWNTIME = false
-
-  def up
-    return unless Gitlab::Database.mysql?
-
-    change_column :gpg_keys, :key, :text, limit: 16.megabytes - 1
-  end
-
-  def down
-    # no-op
-  end
-end

db/migrate/limits_ci_build_trace_chunks_raw_data_for_mysql.rb

-class LimitsCiBuildTraceChunksRawDataForMysql < ActiveRecord::Migration[4.2]
-  def up
-    return unless Gitlab::Database.mysql?
-
-    # Mysql needs MEDIUMTEXT type (up to 16MB) rather than TEXT (up to 64KB)
-    # Because 'raw_data' is always capped by Ci::BuildTraceChunk::CHUNK_SIZE, which is 128KB
-    change_column :ci_build_trace_chunks, :raw_data, :binary, limit: 16.megabytes - 1 # MEDIUMTEXT
-  end
-end

db/migrate/limits_to_mysql.rb

-class LimitsToMysql < ActiveRecord::Migration[4.2]
-  def up
-    return unless ActiveRecord::Base.configurations[Rails.env]['adapter'] =~ /^mysql/
-
-    change_column :snippets, :content, :text, limit: 2147483647
-    change_column :notes, :st_diff, :text, limit: 2147483647
-  end
-end

db/migrate/markdown_cache_limits_to_mysql.rb

-class MarkdownCacheLimitsToMysql < ActiveRecord::Migration[4.2]
-  DOWNTIME = false
-
-  def up
-    return unless Gitlab::Database.mysql?
-
-    change_column :snippets, :content_html, :text, limit: 2147483647
-  end
-
-  def down
-    # no-op
-  end
-end

db/migrate/merge_request_diff_file_limits_to_mysql.rb

-class MergeRequestDiffFileLimitsToMysql < ActiveRecord::Migration[4.2]
-  DOWNTIME = false
-
-  def up
-    return unless Gitlab::Database.mysql?
-
-    change_column :merge_request_diff_files, :diff, :text, limit: 2147483647, default: nil
-  end
-
-  def down
-  end
-end

db/migrate/prometheus_metrics_limits_to_mysql.rb

-class PrometheusMetricsLimitsToMysql < ActiveRecord::Migration[4.2]
-  DOWNTIME = false
-
-  def up
-    return unless Gitlab::Database.mysql?
-
-    change_column :prometheus_metrics, :query, :text, limit: 4096, default: nil
-  end
-
-  def down
-  end
-end

db/post_migrate/20180409170809_populate_missing_project_ci_cd_settings.rb

@@ -9,10 +9,6 @@ class PopulateMissingProjectCiCdSettings < ActiveRecord::Migration[4.2]
   disable_ddl_transaction!
 
   def up
-    # MySQL does not support online upgrades, thus there can't be any missing
-    # rows.
-    return if Gitlab::Database.mysql?
-
     # Projects created after the initial migration but before the code started
     # using ProjectCiCdSetting won't have a corresponding row in
     # project_ci_cd_settings, so let's fix that.

db/post_migrate/20181219130552_update_project_import_visibility_level.rb

@@ -49,7 +49,7 @@ class UpdateProjectImportVisibilityLevel < ActiveRecord::Migration[5.0]
   def update_projects_visibility(visibility)
     say_with_time("Updating project visibility to #{visibility} on #{Project::IMPORT_TYPE} imports.") do
       Project.with_group_visibility(visibility).select(:id).each_batch(of: BATCH_SIZE) do |batch, _index|
-        batch_sql = Gitlab::Database.mysql? ? batch.pluck(:id).join(', ') : batch.select(:id).to_sql
+        batch_sql = batch.select(:id).to_sql
 
         say("Updating #{batch.size} items.", true)
 

db/post_migrate/20190204115450_migrate_auto_dev_ops_domain_to_cluster_domain.rb

@@ -16,26 +16,6 @@ class MigrateAutoDevOpsDomainToClusterDomain < ActiveRecord::Migration[5.0]
   private
 
   def update_clusters_domain_query
-    if Gitlab::Database.mysql?
-      mysql_query
-    else
-      postgresql_query
-    end
-  end
-
-  def mysql_query
-    <<~HEREDOC
-    UPDATE clusters, project_auto_devops, cluster_projects
-    SET
-      clusters.domain = project_auto_devops.domain
-    WHERE
-      cluster_projects.cluster_id = clusters.id
-      AND project_auto_devops.project_id = cluster_projects.project_id
-      AND project_auto_devops.domain != ''
-    HEREDOC
-  end
-
-  def postgresql_query
     <<~HEREDOC
     UPDATE clusters
     SET domain = project_auto_devops.domain

db/post_migrate/20190404143330_add_unique_constraint_to_approvals_user_id_and_merge_request_id.rb

@@ -21,34 +21,18 @@ class AddUniqueConstraintToApprovalsUserIdAndMergeRequestId < ActiveRecord::Migr
   def remove_duplicates
     add_concurrent_index :approvals, [:user_id, :merge_request_id, :id]
 
-    if Gitlab::Database.mysql?
-      execute <<-SQL
-        DELETE FROM a
-        USING approvals AS a
-        INNER JOIN (
-          SELECT user_id, merge_request_id, MIN(id) as min_id
-          FROM approvals
-          GROUP BY user_id, merge_request_id
-          HAVING COUNT(id) > 1
-        ) as approvals_with_duplicates
-        ON approvals_with_duplicates.user_id = a.user_id
-        AND approvals_with_duplicates.merge_request_id = a.merge_request_id
-        WHERE approvals_with_duplicates.min_id <> a.id;
-      SQL
-    else
-      execute <<-SQL
-        DELETE FROM approvals
-        USING (
-          SELECT user_id, merge_request_id, MIN(id) as min_id
-          FROM approvals
-          GROUP BY user_id, merge_request_id
-          HAVING COUNT(id) > 1
-        ) as approvals_with_duplicates
-        WHERE approvals_with_duplicates.user_id = approvals.user_id
-        AND approvals_with_duplicates.merge_request_id = approvals.merge_request_id
-        AND approvals_with_duplicates.min_id <> approvals.id;
-      SQL
-    end
+    execute <<-SQL
+      DELETE FROM approvals
+      USING (
+        SELECT user_id, merge_request_id, MIN(id) as min_id
+        FROM approvals
+        GROUP BY user_id, merge_request_id
+        HAVING COUNT(id) > 1
+      ) as approvals_with_duplicates
+      WHERE approvals_with_duplicates.user_id = approvals.user_id
+      AND approvals_with_duplicates.merge_request_id = approvals.merge_request_id
+      AND approvals_with_duplicates.min_id <> approvals.id;
+    SQL
 
     remove_concurrent_index :approvals, [:user_id, :merge_request_id, :id]
   end

lib/api/entities.rb

@@ -1052,15 +1052,8 @@ module API
       # rubocop: disable CodeReuse/ActiveRecord
       def self.preload_relation(projects_relation, options = {})
         relation = super(projects_relation, options)
-
-        # MySQL doesn't support LIMIT inside an IN subquery
-        if Gitlab::Database.mysql?
-          project_ids = relation.pluck('projects.id')
-          namespace_ids = relation.pluck(:namespace_id)
-        else
-          project_ids = relation.select('projects.id')
-          namespace_ids = relation.select(:namespace_id)
-        end
+        project_ids = relation.select('projects.id')
+        namespace_ids = relation.select(:namespace_id)
 
         options[:project_members] = options[:current_user]
           .project_members

lib/backup/database.rb

@@ -23,11 +23,6 @@ module Backup
 
       dump_pid =
         case config["adapter"]
-        when /^mysql/ then
-          progress.print "Dumping MySQL database #{config['database']} ... "
-          # Workaround warnings from MySQL 5.6 about passwords on cmd line
-          ENV['MYSQL_PWD'] = config["password"].to_s if config["password"]
-          spawn('mysqldump', *mysql_args, config['database'], out: compress_wr)
         when "postgresql" then
           progress.print "Dumping PostgreSQL database #{config['database']} ... "
           pg_env
@@ -57,11 +52,6 @@ module Backup
 
       restore_pid =
         case config["adapter"]
-        when /^mysql/ then
-          progress.print "Restoring MySQL database #{config['database']} ... "
-          # Workaround warnings from MySQL 5.6 about passwords on cmd line
-          ENV['MYSQL_PWD'] = config["password"].to_s if config["password"]
-          spawn('mysql', *mysql_args, config['database'], in: decompress_rd)
         when "postgresql" then
           progress.print "Restoring PostgreSQL database #{config['database']} ... "
           pg_env
@@ -80,23 +70,6 @@ module Backup
 
     protected
 
-    def mysql_args
-      args = {
-        'host'      => '--host',
-        'port'      => '--port',
-        'socket'    => '--socket',
-        'username'  => '--user',
-        'encoding'  => '--default-character-set',
-        # SSL
-        'sslkey'    => '--ssl-key',
-        'sslcert'   => '--ssl-cert',
-        'sslca'     => '--ssl-ca',
-        'sslcapath' => '--ssl-capath',
-        'sslcipher' => '--ssl-cipher'
-      }
-      args.map { |opt, arg| "#{arg}=#{config[opt]}" if config[opt] }.compact
-    end
-
     def pg_env
       args = {
         'username'  => 'PGUSER',

lib/forever.rb

 # frozen_string_literal: true
 
 class Forever
-  POSTGRESQL_DATE = DateTime.new(3000, 1, 1)
-  MYSQL_DATE = DateTime.new(2038, 01, 19)
+  DATE = DateTime.new(3000, 1, 1)
 
-  # MySQL timestamp has a range of '1970-01-01 00:00:01' UTC to '2038-01-19 03:14:07' UTC
   def self.date
-    if Gitlab::Database.postgresql?
-      POSTGRESQL_DATE
-    else
-      MYSQL_DATE
-    end
+    DATE
   end
 end

lib/gitlab/background_migration/fill_valid_time_for_pages_domain_certificate.rb

@@ -19,18 +19,11 @@ module Gitlab
 
       def perform(start_id, stop_id)
         PagesDomain.where(id: start_id..stop_id).find_each do |domain|
-          if Gitlab::Database.mysql?
-            domain.update_columns(
-              certificate_valid_not_before: domain.x509&.not_before,
-              certificate_valid_not_after: domain.x509&.not_after
-            )
-          else
-            # for some reason activerecord doesn't append timezone, iso8601 forces this
-            domain.update_columns(
-              certificate_valid_not_before: domain.x509&.not_before&.iso8601,
-              certificate_valid_not_after: domain.x509&.not_after&.iso8601
-            )
-          end
+          # for some reason activerecord doesn't append timezone, iso8601 forces this
+          domain.update_columns(
+            certificate_valid_not_before: domain.x509&.not_before&.iso8601,
+            certificate_valid_not_after: domain.x509&.not_after&.iso8601
+          )
         rescue => e
           Rails.logger.error "Failed to update pages domain certificate valid time. id: #{domain.id}, message: #{e.message}" # rubocop:disable Gitlab/RailsLogger
         end

lib/gitlab/background_migration/populate_untracked_uploads_dependencies.rb

@@ -176,23 +176,12 @@ module Gitlab
         self.table_name = 'projects'
 
         def self.find_by_full_path(path)
-          binary = Gitlab::Database.mysql? ? 'BINARY' : ''
-          order_sql = "(CASE WHEN #{binary} routes.path = #{connection.quote(path)} THEN 0 ELSE 1 END)"
+          order_sql = "(CASE WHEN routes.path = #{connection.quote(path)} THEN 0 ELSE 1 END)"
           where_full_path_in(path).reorder(order_sql).take
         end
 
         def self.where_full_path_in(path)
-          cast_lower = Gitlab::Database.postgresql?
-
-          path = connection.quote(path)
-
-          where =
-            if cast_lower
-              "(LOWER(routes.path) = LOWER(#{path}))"
-            else
-              "(routes.path = #{path})"
-            end
-
+          where = "(LOWER(routes.path) = LOWER(#{connection.quote(path)}))"
           joins("INNER JOIN routes ON routes.source_id = projects.id AND routes.source_type = 'Project'").where(where)
         end
       end

lib/gitlab/background_migration/prepare_untracked_uploads.rb

@@ -133,12 +133,9 @@ module Gitlab
       def insert_sql(file_paths)
         if postgresql_pre_9_5?
           "INSERT INTO #{table_columns_and_values_for_insert(file_paths)};"
-        elsif postgresql?
+        else
           "INSERT INTO #{table_columns_and_values_for_insert(file_paths)}"\
             " ON CONFLICT DO NOTHING;"
-        else # MySQL
-          "INSERT IGNORE INTO"\
-            " #{table_columns_and_values_for_insert(file_paths)};"
         end
       end
 

lib/gitlab/database.rb

@@ -4,13 +4,13 @@ module Gitlab
   module Database
     include Gitlab::Metrics::Methods
 
-    # The max value of INTEGER type is the same between MySQL and PostgreSQL:
     # https://www.postgresql.org/docs/9.2/static/datatype-numeric.html
-    # http://dev.mysql.com/doc/refman/5.7/en/integer-types.html
     MAX_INT_VALUE = 2147483647
+
     # The max value between MySQL's TIMESTAMP and PostgreSQL's timestampz:
     # https://www.postgresql.org/docs/9.1/static/datatype-datetime.html
     # https://dev.mysql.com/doc/refman/5.7/en/datetime.html
+    # FIXME: this should just be the max value of timestampz
     MAX_TIMESTAMP_VALUE = Time.at((1 << 31) - 1).freeze
 
     # Minimum schema version from which migrations are supported
@@ -39,11 +39,11 @@ module Gitlab
     end
 
     def self.human_adapter_name
-      postgresql? ? 'PostgreSQL' : 'MySQL'
-    end
-
-    def self.mysql?
-      adapter_name.casecmp('mysql2').zero?
+      if postgresql?
+        'PostgreSQL'
+      else
+        'Unknown'
+      end
     end
 
     def self.postgresql?
@@ -60,15 +60,14 @@ module Gitlab
 
     # Check whether the underlying database is in read-only mode
     def self.db_read_only?
-      if postgresql?
-        pg_is_in_recovery =
-          ActiveRecord::Base.connection.execute('SELECT pg_is_in_recovery()')
-            .first.fetch('pg_is_in_recovery')
+      pg_is_in_recovery =
+        ActiveRecord::Base
+          .connection
+          .execute('SELECT pg_is_in_recovery()')
+          .first
+          .fetch('pg_is_in_recovery')
 
-        Gitlab::Utils.to_boolean(pg_is_in_recovery)
-      else
-        false
-      end
+      Gitlab::Utils.to_boolean(pg_is_in_recovery)
     end
 
     def self.db_read_write?
@@ -118,51 +117,23 @@ module Gitlab
     end
 
     def self.nulls_last_order(field, direction = 'ASC')
-      order = "#{field} #{direction}"
-
-      if postgresql?
-        order = "#{order} NULLS LAST"
-      else
-        # `field IS NULL` will be `0` for non-NULL columns and `1` for NULL
-        # columns. In the (default) ascending order, `0` comes first.
-        order = "#{field} IS NULL, #{order}" if direction == 'ASC'
-      end
-
-      Arel.sql(order)
+      Arel.sql("#{field} #{direction} NULLS LAST")
     end
 
     def self.nulls_first_order(field, direction = 'ASC')
-      order = "#{field} #{direction}"
-
-      if postgresql?
-        order = "#{order} NULLS FIRST"
-      else
-        # `field IS NULL` will be `0` for non-NULL columns and `1` for NULL
-        # columns. In the (default) ascending order, `0` comes first.
-        order = "#{field} IS NULL, #{order}" if direction == 'DESC'
-      end
-
-      Arel.sql(order)
+      Arel.sql("#{field} #{direction} NULLS FIRST")
     end
 
     def self.random
-      postgresql? ? "RANDOM()" : "RAND()"
+      "RANDOM()"
     end
 
     def self.true_value
-      if postgresql?
-        "'t'"
-      else
-        1
-      end
+      "'t'"
     end
 
     def self.false_value
-      if postgresql?
-        "'f'"
-      else
-        0
-      end
+      "'f'"
     end
 
     def self.with_connection_pool(pool_size)
@@ -182,7 +153,7 @@ module Gitlab
     # rows - An Array of Hash instances, each mapping the columns to their
     #        values.
     # return_ids - When set to true the return value will be an Array of IDs of
-    #              the inserted rows, this only works on PostgreSQL.
+    #              the inserted rows
     # disable_quote - A key or an Array of keys to exclude from quoting (You
     #                 become responsible for protection from SQL injection for
     #                 these keys!)
@@ -191,7 +162,6 @@ module Gitlab
 
       keys = rows.first.keys
       columns = keys.map { |key| connection.quote_column_name(key) }
-      return_ids = false if mysql?
 
       disable_quote = Array(disable_quote).to_set
       tuples = rows.map do |row|
@@ -258,11 +228,7 @@ module Gitlab
     def self.database_version
       row = connection.execute("SELECT VERSION()").first
 
-      if postgresql?
-        row['version']
-      else
-        row.first
-      end
+      row['version']
     end
 
     private_class_method :database_version

lib/gitlab/database/date_time.rb

@@ -7,8 +7,7 @@ module Gitlab
       # the first of the `start_time_attrs` that isn't NULL. `SELECT` the resulting interval
       # along with an alias specified by the `as` parameter.
       #
-      # Note: For MySQL, the interval is returned in seconds.
-      #       For PostgreSQL, the interval is returned as an INTERVAL type.
+      # Note: the interval is returned as an INTERVAL type.
       def subtract_datetimes(query_so_far, start_time_attrs, end_time_attrs, as)
         diff_fn = subtract_datetimes_diff(query_so_far, start_time_attrs, end_time_attrs)
 
@@ -16,17 +15,10 @@ module Gitlab
       end
 
       def subtract_datetimes_diff(query_so_far, start_time_attrs, end_time_attrs)
-        if Gitlab::Database.postgresql?
-          Arel::Nodes::Subtraction.new(
-            Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(end_time_attrs)),
-            Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(start_time_attrs)))
-        elsif Gitlab::Database.mysql?
-          Arel::Nodes::NamedFunction.new(
-            "TIMESTAMPDIFF",
-            [Arel.sql('second'),
-             Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(start_time_attrs)),
-             Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(end_time_attrs))])
-        end
+        Arel::Nodes::Subtraction.new(
+          Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(end_time_attrs)),
+          Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(start_time_attrs))
+        )
       end
     end
   end

lib/gitlab/database/median.rb

@@ -17,13 +17,9 @@ module Gitlab
       def extract_median(results)
         result = results.compact.first
 
-        if Gitlab::Database.postgresql?
-          result = result.first.presence
+        result = result.first.presence
 
-          result['median']&.to_f if result
-        elsif Gitlab::Database.mysql?
-          result.to_a.flatten.first
-        end
+        result['median']&.to_f if result
       end
 
       def extract_medians(results)
@@ -34,31 +30,6 @@ module Gitlab
         end
       end
 
-      def mysql_median_datetime_sql(arel_table, query_so_far, column_sym)
-        query = arel_table.from
-                .from(arel_table.project(Arel.sql('*')).order(arel_table[column_sym]).as(arel_table.table_name))
-                .project(average([arel_table[column_sym]], 'median'))
-                .where(
-                  Arel::Nodes::Between.new(
-                    Arel.sql("(select @row_id := @row_id + 1)"),
-                    Arel::Nodes::And.new(
-                      [Arel.sql('@ct/2.0'),
-                       Arel.sql('@ct/2.0 + 1')]
-                    )
-                  )
-                ).
-                # Disallow negative values
-                where(arel_table[column_sym].gteq(0))
-
-        [
-          Arel.sql("CREATE TEMPORARY TABLE IF NOT EXISTS #{query_so_far.to_sql}"),
-          Arel.sql("set @ct := (select count(1) from #{arel_table.table_name});"),
-          Arel.sql("set @row_id := 0;"),
-          query.to_sql,
-          Arel.sql("DROP TEMPORARY TABLE IF EXISTS #{arel_table.table_name};")
-        ]
-      end
-
       def pg_median_datetime_sql(arel_table, query_so_far, column_sym, partition_column = nil)
         # Create a CTE with the column we're operating on, row number (after sorting by the column
         # we're operating on), and count of the table we're operating on (duplicated across) all rows
@@ -113,18 +84,8 @@ module Gitlab
 
       private
 
-      def median_queries(arel_table, query_so_far, column_sym, partition_column = nil)
-        if Gitlab::Database.postgresql?
-          pg_median_datetime_sql(arel_table, query_so_far, column_sym, partition_column)
-        elsif Gitlab::Database.mysql?
-          raise NotSupportedError, "partition_column is not supported for MySQL" if partition_column
-
-          mysql_median_datetime_sql(arel_table, query_so_far, column_sym)
-        end
-      end
-
       def execute_queries(arel_table, query_so_far, column_sym, partition_column = nil)
-        queries = median_queries(arel_table, query_so_far, column_sym, partition_column)
+        queries = pg_median_datetime_sql(arel_table, query_so_far, column_sym, partition_column)
 
         Array.wrap(queries).map { |query| ActiveRecord::Base.connection.execute(query) }
       end

lib/gitlab/database/migration_helpers.rb

@@ -68,10 +68,7 @@ module Gitlab
         end
       end
 
-      # Creates a new index, concurrently when supported
-      #
-      # On PostgreSQL this method creates an index concurrently, on MySQL this
-      # creates a regular index.
+      # Creates a new index, concurrently
       #
       # Example:
       #
@@ -85,9 +82,7 @@ module Gitlab
             'in the body of your migration class'
         end
 
-        if Database.postgresql?
-          options = options.merge({ algorithm: :concurrently })
-        end
+        options = options.merge({ algorithm: :concurrently })
 
         if index_exists?(table_name, column_name, options)
           Rails.logger.warn "Index not created because it already exists (this may be due to an aborted migration or similar): table_name: #{table_name}, column_name: #{column_name}" # rubocop:disable Gitlab/RailsLogger
@@ -99,9 +94,7 @@ module Gitlab
         end
       end
 
-      # Removes an existed index, concurrently when supported
-      #
-      # On PostgreSQL this method removes an index concurrently.
+      # Removes an existed index, concurrently
       #
       # Example:
       #
@@ -129,9 +122,7 @@ module Gitlab
         end
       end
 
-      # Removes an existing index, concurrently when supported
-      #
-      # On PostgreSQL this method removes an index concurrently.
+      # Removes an existing index, concurrently
       #
       # Example:
       #
@@ -170,8 +161,7 @@ module Gitlab
 
       # Adds a foreign key with only minimal locking on the tables involved.
       #
-      # This method only requires minimal locking when using PostgreSQL. When
-      # using MySQL this method will use Rails' default `add_foreign_key`.
+      # This method only requires minimal locking
       #
       # source - The source table containing the foreign key.
       # target - The target table the key points to.
@@ -187,27 +177,7 @@ module Gitlab
           raise 'add_concurrent_foreign_key can not be run inside a transaction'
         end
 
-        # While MySQL does allow disabling of foreign keys it has no equivalent
-        # of PostgreSQL's "VALIDATE CONSTRAINT". As a result we'll just fall
-        # back to the normal foreign key procedure.
-        if Database.mysql?
-          if foreign_key_exists?(source, target, column: column)
-            Rails.logger.warn "Foreign key not created because it exists already " \
-              "(this may be due to an aborted migration or similar): " \
-              "source: #{source}, target: #{target}, column: #{column}"
-            return
-          end
-
-          key_options = { column: column, on_delete: on_delete }
-
-          # The MySQL adapter tries to create a foreign key without a name when
-          # `:name` is nil, instead of generating a name for us.
-          key_options[:name] = name if name
-
-          return add_foreign_key(source, target, key_options)
-        else
-          on_delete = 'SET NULL' if on_delete == :nullify
-        end
+        on_delete = 'SET NULL' if on_delete == :nullify
 
         key_name = name || concurrent_foreign_key_name(source, column)
 
@@ -265,7 +235,7 @@ module Gitlab
 
       # Long-running migrations may take more than the timeout allowed by
       # the database. Disable the session's statement timeout to ensure
-      # migrations don't get killed prematurely. (PostgreSQL only)
+      # migrations don't get killed prematurely.
       #
       # There are two possible ways to disable the statement timeout:
       #
@@ -277,15 +247,6 @@ module Gitlab
       # otherwise the statement will still be disabled until connection is dropped
       # or `RESET ALL` is executed
       def disable_statement_timeout
-        # bypass disabled_statement logic when not using postgres, but still execute block when one is given
-        unless Database.postgresql?
-          if block_given?
-            yield
-          end
-
-          return
-        end
-
         if block_given?
           begin
             execute('SET statement_timeout TO 0')
@@ -535,13 +496,12 @@ module Gitlab
         quoted_old = quote_column_name(old_column)
         quoted_new = quote_column_name(new_column)
 
-        if Database.postgresql?
-          install_rename_triggers_for_postgresql(trigger_name, quoted_table,
-                                                 quoted_old, quoted_new)
-        else
-          install_rename_triggers_for_mysql(trigger_name, quoted_table,
-                                            quoted_old, quoted_new)
-        end
+        install_rename_triggers_for_postgresql(
+          trigger_name,
+          quoted_table,
+          quoted_old,
+          quoted_new
+        )
       end
 
       # Changes the type of a column concurrently.
@@ -584,11 +544,7 @@ module Gitlab
 
         check_trigger_permissions!(table)
 
-        if Database.postgresql?
-          remove_rename_triggers_for_postgresql(table, trigger_name)
-        else
-          remove_rename_triggers_for_mysql(trigger_name)
-        end
+        remove_rename_triggers_for_postgresql(table, trigger_name)
 
         remove_column(table, old)
       end
@@ -801,38 +757,12 @@ module Gitlab
         EOF
       end
 
-      # Installs the triggers necessary to perform a concurrent column rename on
-      # MySQL.
-      def install_rename_triggers_for_mysql(trigger, table, old, new)
-        execute <<-EOF.strip_heredoc
-        CREATE TRIGGER #{trigger}_insert
-        BEFORE INSERT
-        ON #{table}
-        FOR EACH ROW
-        SET NEW.#{new} = NEW.#{old}
-        EOF
-
-        execute <<-EOF.strip_heredoc
-        CREATE TRIGGER #{trigger}_update
-        BEFORE UPDATE
-        ON #{table}
-        FOR EACH ROW
-        SET NEW.#{new} = NEW.#{old}
-        EOF
-      end
-
       # Removes the triggers used for renaming a PostgreSQL column concurrently.
       def remove_rename_triggers_for_postgresql(table, trigger)
         execute("DROP TRIGGER IF EXISTS #{trigger} ON #{table}")
         execute("DROP FUNCTION IF EXISTS #{trigger}()")
       end
 
-      # Removes the triggers used for renaming a MySQL column concurrently.
-      def remove_rename_triggers_for_mysql(trigger)
-        execute("DROP TRIGGER IF EXISTS #{trigger}_insert")
-        execute("DROP TRIGGER IF EXISTS #{trigger}_update")
-      end
-
       # Returns the (base) name to use for triggers when renaming columns.
       def rename_trigger_name(table, old, new)
         'trigger_' + Digest::SHA256.hexdigest("#{table}_#{old}_#{new}").first(12)
@@ -882,8 +812,6 @@ module Gitlab
             order: index.orders
           }
 
-          # These options are not supported by MySQL, so we only add them if
-          # they were previously set.
           options[:using] = index.using if index.using
           options[:where] = index.where if index.where
 
@@ -923,26 +851,16 @@ module Gitlab
       end
 
       # This will replace the first occurrence of a string in a column with
-      # the replacement
-      # On postgresql we can use `regexp_replace` for that.
-      # On mysql we find the location of the pattern, and overwrite it
-      # with the replacement
+      # the replacement using `regexp_replace`
       def replace_sql(column, pattern, replacement)
         quoted_pattern = Arel::Nodes::Quoted.new(pattern.to_s)
         quoted_replacement = Arel::Nodes::Quoted.new(replacement.to_s)
 
-        if Database.mysql?
-          locate = Arel::Nodes::NamedFunction
-            .new('locate', [quoted_pattern, column])
-          insert_in_place = Arel::Nodes::NamedFunction
-            .new('insert', [column, locate, pattern.size, quoted_replacement])
+        replace = Arel::Nodes::NamedFunction.new(
+          "regexp_replace", [column, quoted_pattern, quoted_replacement]
+        )
 
-          Arel::Nodes::SqlLiteral.new(insert_in_place.to_sql)
-        else
-          replace = Arel::Nodes::NamedFunction
-            .new("regexp_replace", [column, quoted_pattern, quoted_replacement])
-          Arel::Nodes::SqlLiteral.new(replace.to_sql)
-        end
+        Arel::Nodes::SqlLiteral.new(replace.to_sql)
       end
 
       def remove_foreign_key_if_exists(*args)
@@ -984,11 +902,7 @@ database (#{dbname}) using a super user and running:
 
     ALTER #{user} WITH SUPERUSER
 
-For MySQL you instead need to run:
-
-    GRANT ALL PRIVILEGES ON #{dbname}.* TO #{user}@'%'
-
-Both queries will grant the user super user permissions, ensuring you don't run
+This query will grant the user super user permissions, ensuring you don't run
 into similar problems in the future (e.g. when new tables are created).
           EOF
         end
@@ -1091,10 +1005,6 @@ into similar problems in the future (e.g. when new tables are created).
       # This will include indexes using an expression on the column, for example:
       # `CREATE INDEX CONCURRENTLY index_name ON table (LOWER(column));`
       #
-      # For mysql, it falls back to the default ActiveRecord implementation that
-      # will not find custom indexes. But it will select by name without passing
-      # a column.
-      #
       # We can remove this when upgrading to Rails 5 with an updated `index_exists?`:
       # - https://github.com/rails/rails/commit/edc2b7718725016e988089b5fb6d6fb9d6e16882
       #
@@ -1105,10 +1015,8 @@ into similar problems in the future (e.g. when new tables are created).
         # does not find indexes without passing a column name.
         if indexes(table).map(&:name).include?(index.to_s)
           true
-        elsif Gitlab::Database.postgresql?
-          postgres_exists_by_name?(table, index)
         else
-          false
+          postgres_exists_by_name?(table, index)
         end
       end
 
@@ -1124,10 +1032,6 @@ into similar problems in the future (e.g. when new tables are created).
         connection.select_value(index_sql).to_i > 0
       end
 
-      def mysql_compatible_index_length
-        Gitlab::Database.mysql? ? 20 : nil
-      end
-
       private
 
       def validate_timestamp_column_name!(column_name)

lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb

@@ -51,14 +51,10 @@ module Gitlab
             quoted_old_full_path = quote_string(old_full_path)
             quoted_old_wildcard_path = quote_string("#{old_full_path}/%")
 
-            filter = if Database.mysql?
-                       "lower(routes.path) = lower('#{quoted_old_full_path}') "\
-                       "OR routes.path LIKE '#{quoted_old_wildcard_path}'"
-                     else
-                       "routes.id IN "\
-                       "( SELECT routes.id FROM routes WHERE lower(routes.path) = lower('#{quoted_old_full_path}') "\
-                       "UNION SELECT routes.id FROM routes WHERE routes.path ILIKE '#{quoted_old_wildcard_path}' )"
-                     end
+            filter =
+              "routes.id IN "\
+              "( SELECT routes.id FROM routes WHERE lower(routes.path) = lower('#{quoted_old_full_path}') "\
+              "UNION SELECT routes.id FROM routes WHERE routes.path ILIKE '#{quoted_old_wildcard_path}' )"
 
             replace_statement = replace_sql(Route.arel_table[:path],
                                             old_full_path,

lib/gitlab/import/database_helpers.rb

@@ -6,9 +6,7 @@ module Gitlab
       # Inserts a raw row and returns the ID of the inserted row.
       #
       # attributes - The attributes/columns to set.
-      # relation - An ActiveRecord::Relation to use for finding the ID of the row
-      #            when using MySQL.
-      # rubocop: disable CodeReuse/ActiveRecord
+      # relation - An ActiveRecord::Relation to use for finding the table name
       def insert_and_return_id(attributes, relation)
         # We use bulk_insert here so we can bypass any queries executed by
         # callbacks or validation rules, as doing this wouldn't scale when
@@ -16,12 +14,8 @@ module Gitlab
         result = Gitlab::Database
                  .bulk_insert(relation.table_name, [attributes], return_ids: true)
 
-        # MySQL doesn't support returning the IDs of a bulk insert in a way that
-        # is not a pain, so in this case we'll issue an extra query instead.
-        result.first ||
-          relation.where(iid: attributes[:iid]).limit(1).pluck(:id).first
+        result.first
       end
-      # rubocop: enable CodeReuse/ActiveRecord
     end
   end
 end

lib/mysql_zero_date.rb

-# frozen_string_literal: true
-
-# Disable NO_ZERO_DATE mode for mysql in rails 5.
-# We use zero date as a default value
-# (config/initializers/active_record_mysql_timestamp.rb), in
-# Rails 5 using zero date fails by default (https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/75450216)
-# and NO_ZERO_DATE has to be explicitly disabled. Disabling strict mode
-# is not sufficient.
-
-require 'active_record/connection_adapters/abstract_mysql_adapter'
-
-module MysqlZeroDate
-  def configure_connection
-    super
-
-    @connection.query "SET @@SESSION.sql_mode = REPLACE(@@SESSION.sql_mode, 'NO_ZERO_DATE', '');" # rubocop:disable Gitlab/ModuleWithInstanceVariables
-  end
-end
-
-ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter.prepend(MysqlZeroDate)

lib/serializers/json.rb

 # frozen_string_literal: true
 
 module Serializers
-  # This serializer exports data as JSON,
-  # it is designed to be used with interwork compatibility between MySQL and PostgreSQL
-  # implementations, as used version of MySQL does not support native json type
-  #
-  # Secondly, the loader makes the resulting hash to have deep indifferent access
+  # Make the resulting hash have deep indifferent access
   class JSON
     class << self
       def dump(obj)
-        # MySQL stores data as text
-        # look at ./config/initializers/ar_mysql_jsonb_support.rb
-        if Gitlab::Database.mysql?
-          obj = ActiveSupport::JSON.encode(obj)
-        end
-
         obj
       end
 
       def load(data)
         return if data.nil?
 
-        # On MySQL we store data as text
-        # look at ./config/initializers/ar_mysql_jsonb_support.rb
-        if Gitlab::Database.mysql?
-          data = ActiveSupport::JSON.decode(data)
-        end
-
         Gitlab::Utils.deep_indifferent_access(data)
       end
     end

lib/support/deploy/deploy.sh

@@ -28,7 +28,7 @@ sudo -u git -H git pull origin master
 echo 'Deploy: Bundle and migrate'
 
 # change it to your needs
-sudo -u git -H bundle --without aws development test mysql --deployment
+sudo -u git -H bundle --without aws development test --deployment
 
 sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
 sudo -u git -H bundle exec rake gitlab:assets:clean RAILS_ENV=production

lib/tasks/gitlab/db.rake

@@ -26,12 +26,9 @@ namespace :gitlab do
     task drop_tables: :environment do
       connection = ActiveRecord::Base.connection
 
-      # If MySQL, turn off foreign key checks
-      connection.execute('SET FOREIGN_KEY_CHECKS=0') if Gitlab::Database.mysql?
-
-      # connection.tables is deprecated in MySQLAdapter, but in PostgreSQLAdapter
-      # data_sources returns both views and tables, so use #tables instead
-      tables = Gitlab::Database.mysql? ? connection.data_sources : connection.tables
+      # In PostgreSQLAdapter, data_sources returns both views and tables, so use
+      # #tables instead
+      tables = connection.tables
 
       # Removes the entry from the array
       tables.delete 'schema_migrations'
@@ -40,12 +37,8 @@ namespace :gitlab do
 
       # Drop tables with cascade to avoid dependent table errors
       # PG: http://www.postgresql.org/docs/current/static/ddl-depend.html
-      # MySQL: http://dev.mysql.com/doc/refman/5.7/en/drop-table.html
       # Add `IF EXISTS` because cascade could have already deleted a table.
       tables.each { |t| connection.execute("DROP TABLE IF EXISTS #{connection.quote_table_name(t)} CASCADE") }
-
-      # If MySQL, re-enable foreign key checks
-      connection.execute('SET FOREIGN_KEY_CHECKS=1') if Gitlab::Database.mysql?
     end
 
     desc 'Configures the database by running migrate, or by loading the schema and seeding if needed'

lib/tasks/gitlab/setup.rake

@@ -31,7 +31,6 @@ namespace :gitlab do
     terminate_all_connections unless Rails.env.production?
 
     Rake::Task["db:reset"].invoke
-    Rake::Task["add_limits_mysql"].invoke
     Rake::Task["setup_postgresql"].invoke
     Rake::Task["db:seed_fu"].invoke
   rescue Gitlab::TaskAbortedByUserError

lib/tasks/migrate/add_limits_mysql.rake

-require Rails.root.join('db/migrate/limits_to_mysql')
-require Rails.root.join('db/migrate/markdown_cache_limits_to_mysql')
-require Rails.root.join('db/migrate/merge_request_diff_file_limits_to_mysql')
-require Rails.root.join('db/migrate/limits_ci_build_trace_chunks_raw_data_for_mysql')
-require Rails.root.join('db/migrate/gpg_keys_limits_to_mysql')
-require Rails.root.join('db/migrate/prometheus_metrics_limits_to_mysql')
-
-desc "GitLab | Add limits to strings in mysql database"
-task add_limits_mysql: :environment do
-  puts "Adding limits to schema.rb for mysql"
-  LimitsToMysql.new.up
-  MarkdownCacheLimitsToMysql.new.up
-  MergeRequestDiffFileLimitsToMysql.new.up
-  LimitsCiBuildTraceChunksRawDataForMysql.new.up
-  IncreaseMysqlTextLimitForGpgKeys.new.up
-  PrometheusMetricsLimitsToMysql.new.up
-end

scripts/create_mysql_user.sh

-#!/bin/bash
-
-mysql --user=root --host=mysql <<EOF
-CREATE USER IF NOT EXISTS 'gitlab'@'%';
-GRANT ALL PRIVILEGES ON gitlabhq_test.* TO 'gitlab'@'%';
-FLUSH PRIVILEGES;
-EOF

spec/features/projects/new_project_spec.rb

@@ -62,13 +62,7 @@ describe 'New project' do
         find('#import-project-tab').click
       end
 
-      context 'when using postgres', :postgresql do
-        it { expect(page).to have_link('Manifest file') }
-      end
-
-      context 'when using mysql', :mysql do
-        it { expect(page).not_to have_link('Manifest file') }
-      end
+      it { expect(page).to have_link('Manifest file') }
     end
 
     context 'Visibility level selector', :js do

spec/lib/forever_spec.rb

@@ -4,19 +4,9 @@ describe Forever do
   describe '.date' do
     subject { described_class.date }
 
-    context 'when using PostgreSQL' do
-      it 'returns Postgresql future date' do
-        allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
-
-        expect(subject).to eq(described_class::POSTGRESQL_DATE)
-      end
-    end
-
-    context 'when using MySQL' do
-      it 'returns MySQL future date' do
-        allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
-
-        expect(subject).to eq(described_class::MYSQL_DATE)
+    it 'returns Postgresql future date' do
+      Timecop.travel(Date.new(2999, 12, 31)) do
+        is_expected.to be > Date.today
       end
     end
   end

spec/lib/gitlab/cycle_analytics/usage_data_spec.rb

@@ -28,27 +28,7 @@ describe Gitlab::CycleAnalytics::UsageData do
       end
     end
 
-    shared_examples 'a valid usage data result' do
-      it 'returns the aggregated usage data of every selected project' do
-        result = subject.to_json
-
-        expect(result).to have_key(:avg_cycle_analytics)
-
-        CycleAnalytics::LevelBase::STAGES.each do |stage|
-          expect(result[:avg_cycle_analytics]).to have_key(stage)
-
-          stage_values    = result[:avg_cycle_analytics][stage]
-          expected_values = expect_values_per_stage[stage]
-
-          expected_values.each_pair do |op, value|
-            expect(stage_values).to have_key(op)
-            expect(stage_values[op]).to eq(value)
-          end
-        end
-      end
-    end
-
-    context 'when using postgresql', :postgresql do
+    context 'a valid usage data result' do
       let(:expect_values_per_stage) do
         {
           issue: {
@@ -89,51 +69,23 @@ describe Gitlab::CycleAnalytics::UsageData do
         }
       end
 
-      it_behaves_like 'a valid usage data result'
-    end
+      it 'returns the aggregated usage data of every selected project' do
+        result = subject.to_json
 
-    context 'when using mysql', :mysql do
-      let(:expect_values_per_stage) do
-        {
-          issue: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          plan: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          code: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          test: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          review: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          staging: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          },
-          production: {
-            average: nil,
-            sd: 0,
-            missing: 2
-          }
-        }
-      end
+        expect(result).to have_key(:avg_cycle_analytics)
+
+        CycleAnalytics::LevelBase::STAGES.each do |stage|
+          expect(result[:avg_cycle_analytics]).to have_key(stage)
 
-      it_behaves_like 'a valid usage data result'
+          stage_values    = result[:avg_cycle_analytics][stage]
+          expected_values = expect_values_per_stage[stage]
+
+          expected_values.each_pair do |op, value|
+            expect(stage_values).to have_key(op)
+            expect(stage_values[op]).to eq(value)
+          end
+        end
+      end
     end
   end
 end

spec/lib/gitlab/database/median_spec.rb

-require 'spec_helper'
-
-describe Gitlab::Database::Median do
-  let(:dummy_class) do
-    Class.new do
-      include Gitlab::Database::Median
-    end
-  end
-
-  subject(:median) { dummy_class.new }
-
-  describe '#median_datetimes' do
-    it 'raises NotSupportedError', :mysql do
-      expect { median.median_datetimes(nil, nil, nil, :project_id) }.to raise_error(dummy_class::NotSupportedError, "partition_column is not supported for MySQL")
-    end
-  end
-end

spec/lib/gitlab/database_spec.rb

@@ -24,21 +24,13 @@ describe Gitlab::Database do
       expect(described_class.human_adapter_name).to eq('PostgreSQL')
     end
 
-    it 'returns MySQL when using MySQL' do
+    it 'returns Unknown when using anything else' do
       allow(described_class).to receive(:postgresql?).and_return(false)
 
-      expect(described_class.human_adapter_name).to eq('MySQL')
+      expect(described_class.human_adapter_name).to eq('Unknown')
     end
   end
 
-  # These are just simple smoke tests to check if the methods work (regardless
-  # of what they may return).
-  describe '.mysql?' do
-    subject { described_class.mysql? }
-
-    it { is_expected.to satisfy { |val| val == true || val == false } }
-  end
-
   describe '.postgresql?' do
     subject { described_class.postgresql? }
 
@@ -52,15 +44,6 @@ describe Gitlab::Database do
       described_class.instance_variable_set(:@version, nil)
     end
 
-    context "on mysql" do
-      it "extracts the version number" do
-        allow(described_class).to receive(:database_version)
-          .and_return("5.7.12-standard")
-
-        expect(described_class.version).to eq '5.7.12-standard'
-      end
-    end
-
     context "on postgresql" do
       it "extracts the version number" do
         allow(described_class).to receive(:database_version)
@@ -80,7 +63,7 @@ describe Gitlab::Database do
   end
 
   describe '.postgresql_9_or_less?' do
-    it 'returns false when using MySQL' do
+    it 'returns false when not using postgresql' do
       allow(described_class).to receive(:postgresql?).and_return(false)
 
       expect(described_class.postgresql_9_or_less?).to eq(false)
@@ -134,7 +117,7 @@ describe Gitlab::Database do
   end
 
   describe '.join_lateral_supported?' do
-    it 'returns false when using MySQL' do
+    it 'returns false when not using postgresql' do
       allow(described_class).to receive(:postgresql?).and_return(false)
 
       expect(described_class.join_lateral_supported?).to eq(false)
@@ -156,7 +139,7 @@ describe Gitlab::Database do
   end
 
   describe '.replication_slots_supported?' do
-    it 'returns false when using MySQL' do
+    it 'returns false when not using postgresql' do
       allow(described_class).to receive(:postgresql?).and_return(false)
 
       expect(described_class.replication_slots_supported?).to eq(false)
@@ -248,43 +231,13 @@ describe Gitlab::Database do
   end
 
   describe '.nulls_last_order' do
-    context 'when using PostgreSQL' do
-      before do
-        expect(described_class).to receive(:postgresql?).and_return(true)
-      end
-
-      it { expect(described_class.nulls_last_order('column', 'ASC')).to eq 'column ASC NULLS LAST'}
-      it { expect(described_class.nulls_last_order('column', 'DESC')).to eq 'column DESC NULLS LAST'}
-    end
-
-    context 'when using MySQL' do
-      before do
-        expect(described_class).to receive(:postgresql?).and_return(false)
-      end
-
-      it { expect(described_class.nulls_last_order('column', 'ASC')).to eq 'column IS NULL, column ASC'}
-      it { expect(described_class.nulls_last_order('column', 'DESC')).to eq 'column DESC'}
-    end
+    it { expect(described_class.nulls_last_order('column', 'ASC')).to eq 'column ASC NULLS LAST'}
+    it { expect(described_class.nulls_last_order('column', 'DESC')).to eq 'column DESC NULLS LAST'}
   end
 
   describe '.nulls_first_order' do
-    context 'when using PostgreSQL' do
-      before do
-        expect(described_class).to receive(:postgresql?).and_return(true)
-      end
-
-      it { expect(described_class.nulls_first_order('column', 'ASC')).to eq 'column ASC NULLS FIRST'}
-      it { expect(described_class.nulls_first_order('column', 'DESC')).to eq 'column DESC NULLS FIRST'}
-    end
-
-    context 'when using MySQL' do
-      before do
-        expect(described_class).to receive(:postgresql?).and_return(false)
-      end
-
-      it { expect(described_class.nulls_first_order('column', 'ASC')).to eq 'column ASC'}
-      it { expect(described_class.nulls_first_order('column', 'DESC')).to eq 'column IS NULL, column DESC'}
-    end
+    it { expect(described_class.nulls_first_order('column', 'ASC')).to eq 'column ASC NULLS FIRST'}
+    it { expect(described_class.nulls_first_order('column', 'DESC')).to eq 'column DESC NULLS FIRST'}
   end
 
   describe '.with_connection_pool' do
@@ -394,10 +347,6 @@ describe Gitlab::Database do
     end
 
     context 'when using PostgreSQL' do
-      before do
-        allow(described_class).to receive(:mysql?).and_return(false)
-      end
-
       it 'allows the returning of the IDs of the inserted rows' do
         result = double(:result, values: [['10']])
 
@@ -463,31 +412,15 @@ describe Gitlab::Database do
   end
 
   describe '#true_value' do
-    it 'returns correct value for PostgreSQL' do
-      expect(described_class).to receive(:postgresql?).and_return(true)
-
+    it 'returns correct value' do
       expect(described_class.true_value).to eq "'t'"
     end
-
-    it 'returns correct value for MySQL' do
-      expect(described_class).to receive(:postgresql?).and_return(false)
-
-      expect(described_class.true_value).to eq 1
-    end
   end
 
   describe '#false_value' do
-    it 'returns correct value for PostgreSQL' do
-      expect(described_class).to receive(:postgresql?).and_return(true)
-
+    it 'returns correct value' do
       expect(described_class.false_value).to eq "'f'"
     end
-
-    it 'returns correct value for MySQL' do
-      expect(described_class).to receive(:postgresql?).and_return(false)
-
-      expect(described_class.false_value).to eq 0
-    end
   end
 
   describe '.read_only?' do
@@ -497,43 +430,33 @@ describe Gitlab::Database do
   end
 
   describe '.db_read_only?' do
-    context 'when using PostgreSQL' do
-      before do
-        allow(ActiveRecord::Base.connection).to receive(:execute).and_call_original
-        allow(described_class).to receive(:postgresql?).and_return(true)
-      end
-
-      it 'detects a read only database' do
-        allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => "t" }])
-
-        expect(described_class.db_read_only?).to be_truthy
-      end
+    before do
+      allow(ActiveRecord::Base.connection).to receive(:execute).and_call_original
+      allow(described_class).to receive(:postgresql?).and_return(true)
+    end
 
-      it 'detects a read only database' do
-        allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => true }])
+    it 'detects a read only database' do
+      allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => "t" }])
 
-        expect(described_class.db_read_only?).to be_truthy
-      end
+      expect(described_class.db_read_only?).to be_truthy
+    end
 
-      it 'detects a read write database' do
-        allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => "f" }])
+    it 'detects a read only database' do
+      allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => true }])
 
-        expect(described_class.db_read_only?).to be_falsey
-      end
+      expect(described_class.db_read_only?).to be_truthy
+    end
 
-      it 'detects a read write database' do
-        allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => false }])
+    it 'detects a read write database' do
+      allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => "f" }])
 
-        expect(described_class.db_read_only?).to be_falsey
-      end
+      expect(described_class.db_read_only?).to be_falsey
     end
 
-    context 'when using MySQL' do
-      before do
-        expect(described_class).to receive(:postgresql?).and_return(false)
-      end
+    it 'detects a read write database' do
+      allow(ActiveRecord::Base.connection).to receive(:execute).with('SELECT pg_is_in_recovery()').and_return([{ "pg_is_in_recovery" => false }])
 
-      it { expect(described_class.db_read_only?).to be_falsey }
+      expect(described_class.db_read_only?).to be_falsey
     end
   end
 

spec/lib/gitlab/import/database_helpers_spec.rb

@@ -15,32 +15,15 @@ describe Gitlab::Import::DatabaseHelpers do
     let(:attributes) { { iid: 1, title: 'foo' } }
     let(:project) { create(:project) }
 
-    context 'on PostgreSQL' do
-      it 'returns the ID returned by the query' do
-        expect(Gitlab::Database)
-          .to receive(:bulk_insert)
-          .with(Issue.table_name, [attributes], return_ids: true)
-          .and_return([10])
+    it 'returns the ID returned by the query' do
+      expect(Gitlab::Database)
+        .to receive(:bulk_insert)
+        .with(Issue.table_name, [attributes], return_ids: true)
+        .and_return([10])
 
-        id = subject.insert_and_return_id(attributes, project.issues)
+      id = subject.insert_and_return_id(attributes, project.issues)
 
-        expect(id).to eq(10)
-      end
-    end
-
-    context 'on MySQL' do
-      it 'uses a separate query to retrieve the ID' do
-        issue = create(:issue, project: project, iid: attributes[:iid])
-
-        expect(Gitlab::Database)
-          .to receive(:bulk_insert)
-          .with(Issue.table_name, [attributes], return_ids: true)
-          .and_return([])
-
-        id = subject.insert_and_return_id(attributes, project.issues)
-
-        expect(id).to eq(issue.id)
-      end
+      expect(id).to eq(10)
     end
   end
 end

spec/lib/serializers/json_spec.rb

@@ -6,24 +6,8 @@ describe Serializers::JSON do
 
     subject { described_class.dump(obj) }
 
-    context 'when MySQL is used' do
-      before do
-        allow(Gitlab::Database).to receive(:adapter_name) { 'mysql2' }
-      end
-
-      it 'encodes as string' do
-        is_expected.to eq('{"key":"value"}')
-      end
-    end
-
-    context 'when PostgreSQL is used' do
-      before do
-        allow(Gitlab::Database).to receive(:adapter_name) { 'postgresql' }
-      end
-
-      it 'returns a hash' do
-        is_expected.to eq(obj)
-      end
+    it 'returns a hash' do
+      is_expected.to eq(obj)
     end
   end
 
@@ -31,7 +15,13 @@ describe Serializers::JSON do
     let(:data_string) { '{"key":"value","variables":[{"key":"VAR1","value":"VALUE1"}]}' }
     let(:data_hash) { JSON.parse(data_string) }
 
-    shared_examples 'having consistent accessor' do
+    context 'when loading a hash' do
+      subject { described_class.load(data_hash) }
+
+      it 'decodes a string' do
+        is_expected.to be_a(Hash)
+      end
+
       it 'allows to access with symbols' do
         expect(subject[:key]).to eq('value')
         expect(subject[:variables].first[:key]).to eq('VAR1')
@@ -43,59 +33,11 @@ describe Serializers::JSON do
       end
     end
 
-    context 'when MySQL is used' do
-      before do
-        allow(Gitlab::Database).to receive(:adapter_name) { 'mysql2' }
-      end
-
-      context 'when loading a string' do
-        subject { described_class.load(data_string) }
-
-        it 'decodes a string' do
-          is_expected.to be_a(Hash)
-        end
-
-        it_behaves_like 'having consistent accessor'
-      end
-
-      context 'when loading a different type' do
-        subject { described_class.load({ key: 'hash' }) }
-
-        it 'raises an exception' do
-          expect { subject }.to raise_error(TypeError)
-        end
-      end
-
-      context 'when loading a nil' do
-        subject { described_class.load(nil) }
-
-        it 'returns nil' do
-          is_expected.to be_nil
-        end
-      end
-    end
-
-    context 'when PostgreSQL is used' do
-      before do
-        allow(Gitlab::Database).to receive(:adapter_name) { 'postgresql' }
-      end
-
-      context 'when loading a hash' do
-        subject { described_class.load(data_hash) }
-
-        it 'decodes a string' do
-          is_expected.to be_a(Hash)
-        end
-
-        it_behaves_like 'having consistent accessor'
-      end
-
-      context 'when loading a nil' do
-        subject { described_class.load(nil) }
+    context 'when loading a nil' do
+      subject { described_class.load(nil) }
 
-        it 'returns nil' do
-          is_expected.to be_nil
-        end
+      it 'returns nil' do
+        is_expected.to be_nil
       end
     end
   end

spec/models/concerns/case_sensitivity_spec.rb

@@ -28,28 +28,13 @@ describe CaseSensitivity do
         .to contain_exactly(model_1)
     end
 
-    # Using `mysql` & `postgresql` metadata-tags here because both adapters build
-    # the query slightly differently
-    context 'for MySQL', :mysql do
-      it 'builds a simple query' do
-        query = model.iwhere(path: %w(MODEL-1 model-2), name: 'model 1').to_sql
-        expected_query = <<~QRY.strip
-        SELECT `namespaces`.* FROM `namespaces` WHERE (`namespaces`.`path` IN ('MODEL-1', 'model-2')) AND (`namespaces`.`name` = 'model 1')
-        QRY
-
-        expect(query).to eq(expected_query)
-      end
-    end
+    it 'builds a query using LOWER' do
+      query = model.iwhere(path: %w(MODEL-1 model-2), name: 'model 1').to_sql
+      expected_query = <<~QRY.strip
+      SELECT \"namespaces\".* FROM \"namespaces\" WHERE (LOWER(\"namespaces\".\"path\") IN (LOWER('MODEL-1'), LOWER('model-2'))) AND (LOWER(\"namespaces\".\"name\") = LOWER('model 1'))
+      QRY
 
-    context 'for PostgreSQL', :postgresql do
-      it 'builds a query using LOWER' do
-        query = model.iwhere(path: %w(MODEL-1 model-2), name: 'model 1').to_sql
-        expected_query = <<~QRY.strip
-        SELECT \"namespaces\".* FROM \"namespaces\" WHERE (LOWER(\"namespaces\".\"path\") IN (LOWER('MODEL-1'), LOWER('model-2'))) AND (LOWER(\"namespaces\".\"name\") = LOWER('model 1'))
-        QRY
-
-        expect(query).to eq(expected_query)
-      end
+      expect(query).to eq(expected_query)
     end
   end
 end

spec/spec_helper.rb

@@ -268,10 +268,6 @@ RSpec.configure do |config|
     example.run if Gitlab::Database.postgresql?
   end
 
-  config.around(:each, :mysql) do |example|
-    example.run if Gitlab::Database.mysql?
-  end
-
   # This makes sure the `ApplicationController#can?` method is stubbed with the
   # original implementation for all view specs.
   config.before(:each, type: :view) do

spec/workers/background_migration_worker_spec.rb

@@ -55,21 +55,13 @@ describe BackgroundMigrationWorker, :sidekiq, :clean_gitlab_redis_shared_state d
   end
 
   describe '#healthy_database?' do
-    context 'using MySQL', :mysql do
-      it 'returns true' do
-        expect(worker.healthy_database?).to eq(true)
-      end
-    end
-
-    context 'using PostgreSQL', :postgresql do
-      context 'when replication lag is too great' do
-        it 'returns false' do
-          allow(Postgresql::ReplicationSlot)
-            .to receive(:lag_too_great?)
-            .and_return(true)
+    context 'when replication lag is too great' do
+      it 'returns false' do
+        allow(Postgresql::ReplicationSlot)
+          .to receive(:lag_too_great?)
+          .and_return(true)
 
-          expect(worker.healthy_database?).to eq(false)
-        end
+        expect(worker.healthy_database?).to eq(false)
       end
 
       context 'when replication lag is small enough' do