Remove dead MySQL code

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

5 files changed, 8 insertions, 62 deletions

diff --git a/app/models/ci/pipeline.rb b/app/models/ci/pipeline.rb
index 2262282e647..c2eb51ba100 100644
--- a/app/models/ci/pipeline.rb
+++ b/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
 
diff --git a/app/models/concerns/case_sensitivity.rb b/app/models/concerns/case_sensitivity.rb
index c93b6589ee7..abddbf1c7e3 100644
--- a/app/models/concerns/case_sensitivity.rb
+++ b/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
diff --git a/app/models/concerns/routable.rb b/app/models/concerns/routable.rb
index 9becab632f3..116e8967651 100644
--- a/app/models/concerns/routable.rb
+++ b/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
 
diff --git a/app/models/deployment.rb b/app/models/deployment.rb
index b69cda4f2f9..68586e7a1fd 100644
--- a/app/models/deployment.rb
+++ b/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
 
diff --git a/app/uploaders/records_uploads.rb b/app/uploaders/records_uploads.rb
index 00b51f92b12..3b2a9d2f80e 100644
--- a/app/uploaders/records_uploads.rb
+++ b/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