3 files changed, 71 insertions, 11 deletions
diff --git a/doc/development/migration_style_guide.md b/doc/development/migration_style_guide.md
index 243ac7f0c98..1e060ffd941 100644
--- a/doc/development/migration_style_guide.md
+++ b/doc/development/migration_style_guide.md
@@ -136,11 +136,14 @@ class MyMigration < ActiveRecord::Migration
   disable_ddl_transaction!
 
   def up
-    remove_concurrent_index :table_name, :column_name if index_exists?(:table_name, :column_name)
+    remove_concurrent_index :table_name, :column_name
   end
 end
 ```
 
+Note that it is not necessary to check if the index exists prior to
+removing it.
+
 ## Adding indexes
 
 If you need to add a unique index please keep in mind there is the possibility
diff --git a/lib/gitlab/database/migration_helpers.rb b/lib/gitlab/database/migration_helpers.rb
index 21287a8efd0..55160ca8708 100644
--- a/lib/gitlab/database/migration_helpers.rb
+++ b/lib/gitlab/database/migration_helpers.rb
@@ -59,6 +59,11 @@ module Gitlab
           disable_statement_timeout
         end
 
+        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}"
+          return
+        end
+
         add_index(table_name, column_name, options)
       end
 
@@ -83,6 +88,11 @@ module Gitlab
           disable_statement_timeout
         end
 
+        unless index_exists?(table_name, column_name, options)
+          Rails.logger.warn "Index not removed because it does not exist (this may be due to an aborted migration or similar): table_name: #{table_name}, column_name: #{column_name}"
+          return
+        end
+
         remove_index(table_name, options.merge({ column: column_name }))
       end
 
@@ -107,6 +117,11 @@ module Gitlab
           disable_statement_timeout
         end
 
+        unless index_exists_by_name?(table_name, index_name)
+          Rails.logger.warn "Index not removed because it does not exist (this may be due to an aborted migration or similar): table_name: #{table_name}, index_name: #{index_name}"
+          return
+        end
+
         remove_index(table_name, options.merge({ name: index_name }))
       end
 
diff --git a/spec/lib/gitlab/database/migration_helpers_spec.rb b/spec/lib/gitlab/database/migration_helpers_spec.rb
index 1de3a14b809..9074e17ae80 100644
--- a/spec/lib/gitlab/database/migration_helpers_spec.rb
+++ b/spec/lib/gitlab/database/migration_helpers_spec.rb
@@ -67,17 +67,35 @@ describe Gitlab::Database::MigrationHelpers do
 
           model.add_concurrent_index(:users, :foo, unique: true)
         end
+
+        it 'does nothing if the index exists already' do
+          expect(model).to receive(:index_exists?)
+            .with(:users, :foo, { algorithm: :concurrently, unique: true }).and_return(true)
+          expect(model).not_to receive(:add_index)
+
+          model.add_concurrent_index(:users, :foo, unique: true)
+        end
       end
 
       context 'using MySQL' do
-        it 'creates a regular index' do
-          expect(Gitlab::Database).to receive(:postgresql?).and_return(false)
+        before do
+          allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
+        end
 
+        it 'creates a regular index' do
           expect(model).to receive(:add_index)
             .with(:users, :foo, {})
 
           model.add_concurrent_index(:users, :foo)
         end
+
+        it 'does nothing if the index exists already' do
+          expect(model).to receive(:index_exists?)
+            .with(:users, :foo, { unique: true }).and_return(true)
+          expect(model).not_to receive(:add_index)
+
+          model.add_concurrent_index(:users, :foo, unique: true)
+        end
       end
     end
 
@@ -95,6 +113,7 @@ describe Gitlab::Database::MigrationHelpers do
     context 'outside a transaction' do
       before do
         allow(model).to receive(:transaction_open?).and_return(false)
+        allow(model).to receive(:index_exists?).and_return(true)
       end
 
       context 'using PostgreSQL' do
@@ -103,18 +122,41 @@ describe Gitlab::Database::MigrationHelpers do
           allow(model).to receive(:disable_statement_timeout)
         end
 
-        it 'removes the index concurrently by column name' do
-          expect(model).to receive(:remove_index)
-            .with(:users, { algorithm: :concurrently, column: :foo })
+        describe 'by column name' do
+          it 'removes the index concurrently' do
+            expect(model).to receive(:remove_index)
+              .with(:users, { algorithm: :concurrently, column: :foo })
 
-          model.remove_concurrent_index(:users, :foo)
+            model.remove_concurrent_index(:users, :foo)
+          end
+
+          it 'does nothing if the index does not exist' do
+            expect(model).to receive(:index_exists?)
+              .with(:users, :foo, { algorithm: :concurrently, unique: true }).and_return(false)
+            expect(model).not_to receive(:remove_index)
+
+            model.remove_concurrent_index(:users, :foo, unique: true)
+          end
         end
 
-        it 'removes the index concurrently by index name' do
-          expect(model).to receive(:remove_index)
-            .with(:users, { algorithm: :concurrently, name: "index_x_by_y" })
+        describe 'by index name' do
+          before do
+            allow(model).to receive(:index_exists_by_name?).with(:users, "index_x_by_y").and_return(true)
+          end
+
+          it 'removes the index concurrently by index name' do
+            expect(model).to receive(:remove_index)
+              .with(:users, { algorithm: :concurrently, name: "index_x_by_y" })
+
+            model.remove_concurrent_index_by_name(:users, "index_x_by_y")
+          end
+
+          it 'does nothing if the index does not exist' do
+            expect(model).to receive(:index_exists_by_name?).with(:users, "index_x_by_y").and_return(false)
+            expect(model).not_to receive(:remove_index)
 
-          model.remove_concurrent_index_by_name(:users, "index_x_by_y")
+            model.remove_concurrent_index_by_name(:users, "index_x_by_y")
+          end
         end
       end