1 files changed, 66 insertions, 0 deletions
diff --git a/db/post_migrate/20180119121225_remove_redundant_pipeline_stages.rb b/db/post_migrate/20180119121225_remove_redundant_pipeline_stages.rb
new file mode 100644
index 00000000000..61ea85eb2a7
--- /dev/null
+++ b/db/post_migrate/20180119121225_remove_redundant_pipeline_stages.rb
@@ -0,0 +1,66 @@
+class RemoveRedundantPipelineStages < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up(attempts: 100)
+    remove_redundant_pipeline_stages!
+    remove_outdated_index!
+    add_unique_index!
+  rescue ActiveRecord::RecordNotUnique
+    retry if (attempts -= 1) > 0
+
+    raise StandardError, <<~EOS
+      Failed to add an unique index to ci_stages, despite retrying the
+      migration 100 times.
+
+      See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16580.
+    EOS
+  end
+
+  def down
+    remove_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
+    add_concurrent_index :ci_stages, [:pipeline_id, :name]
+  end
+
+  private
+
+  def remove_outdated_index!
+    return unless index_exists?(:ci_stages, [:pipeline_id, :name])
+
+    remove_concurrent_index :ci_stages, [:pipeline_id, :name]
+  end
+
+  def add_unique_index!
+    add_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
+  end
+
+  def remove_redundant_pipeline_stages!
+    disable_statement_timeout
+
+    redundant_stages_ids = <<~SQL
+      SELECT id FROM ci_stages WHERE (pipeline_id, name) IN (
+        SELECT pipeline_id, name FROM ci_stages
+          GROUP BY pipeline_id, name HAVING COUNT(*) > 1
+      )
+    SQL
+
+    execute <<~SQL
+      UPDATE ci_builds SET stage_id = NULL WHERE stage_id IN (#{redundant_stages_ids})
+    SQL
+
+    if Gitlab::Database.postgresql?
+      execute <<~SQL
+        DELETE FROM ci_stages WHERE id IN (#{redundant_stages_ids})
+      SQL
+    else # We can't modify a table we are selecting from on MySQL
+      execute <<~SQL
+        DELETE a FROM ci_stages AS a, ci_stages AS b
+          WHERE a.pipeline_id = b.pipeline_id AND a.name = b.name
+            AND a.id <> b.id
+      SQL
+    end
+  end
+end