Use an array for fetching same_family_pipeline_ids

The `OR` on DB causes a significant harm when
fetching data from DB, without an index.

We can alleviate it by using a pure `pluck(:id).

app/models/ci/pipeline.rb

@@ -819,15 +819,8 @@ module Ci
     # If pipeline is a child of another pipeline, include the parent
     # and the siblings, otherwise return only itself and children.
     def same_family_pipeline_ids
-      if (parent = parent_pipeline)
-        Ci::Pipeline.where(id: parent.id)
-          .or(Ci::Pipeline.where(id: parent.child_pipelines.select(:id)))
-          .select(:id)
-      else
-        Ci::Pipeline.where(id: self.id)
-          .or(Ci::Pipeline.where(id: self.child_pipelines.select(:id)))
-          .select(:id)
-      end
+      parent = parent_pipeline || self
+      [parent.id] + parent.child_pipelines.pluck(:id)
     end
 
     def bridge_triggered?

changelogs/unreleased/fix-same-family-pipeline-ids.yml

+---
+title: Use an array for fetching same_family_pipeline_ids
+merge_request: 36883
+author:
+type: fixed

spec/models/ci/pipeline_spec.rb

@@ -2684,7 +2684,7 @@ RSpec.describe Ci::Pipeline, :mailer do
 
     context 'when pipeline is not child nor parent' do
       it 'returns just the pipeline id' do
-        expect(same_family_pipeline_ids).to contain_exactly(pipeline)
+        expect(same_family_pipeline_ids).to contain_exactly(pipeline.id)
       end
     end
 
@@ -2707,7 +2707,7 @@ RSpec.describe Ci::Pipeline, :mailer do
       end
 
       it 'returns parent sibling and self ids' do
-        expect(same_family_pipeline_ids).to contain_exactly(parent, pipeline, sibling)
+        expect(same_family_pipeline_ids).to contain_exactly(parent.id, pipeline.id, sibling.id)
       end
     end
 
@@ -2723,7 +2723,7 @@ RSpec.describe Ci::Pipeline, :mailer do
       end
 
       it 'returns self and child ids' do
-        expect(same_family_pipeline_ids).to contain_exactly(pipeline, child)
+        expect(same_family_pipeline_ids).to contain_exactly(pipeline.id, child.id)
       end
     end
   end