Extend decomposition prometheus metric with information about CI

This adds to `ci_dedicated_primary_connection="true"`
to `gitlab_database_decomposition_gitlab_schemas_used`
to indicate whether the given schemas are evaluated in context
of a Phase 4 rollout.

This allows us to monitor whether partial Phase 4 rollout
properly assigns connections to schemas.

Changelog: added

lib/gitlab/database/load_balancing/configuration.rb

@@ -78,15 +78,15 @@ module Gitlab
         end
 
         def primary_model_or_model_if_enabled
-          if force_no_sharing_primary_model?
+          if use_dedicated_connection?
             @model
           else
             @primary_model || @model
           end
         end
 
-        def force_no_sharing_primary_model?
-          return false unless @primary_model # Doesn't matter since we don't have an overriding primary model
+        def use_dedicated_connection?
+          return true unless @primary_model # We can only use dedicated connection, if re-use of connections is disabled
           return false unless ::Gitlab::SafeRequestStore.active?
 
           ::Gitlab::SafeRequestStore.fetch(:force_no_sharing_primary_model) do

lib/gitlab/database/query_analyzers/gitlab_schemas_metrics.rb

@@ -27,9 +27,15 @@ module Gitlab
             # to reduce amount of labels sort schemas used
             gitlab_schemas = gitlab_schemas.to_a.sort.join(",")
 
+            # Temporary feature to observe relation of `gitlab_schemas` to `db_config_name`
+            # depending on primary model
+            ci_dedicated_primary_connection = ::Ci::ApplicationRecord.connection_class? &&
+              ::Ci::ApplicationRecord.load_balancer.configuration.use_dedicated_connection?
+
             schemas_metrics.increment({
               gitlab_schemas: gitlab_schemas,
-              db_config_name: db_config_name
+              db_config_name: db_config_name,
+              ci_dedicated_primary_connection: ci_dedicated_primary_connection
             })
           end
 

spec/lib/gitlab/database/query_analyzers/gitlab_schemas_metrics_spec.rb

@@ -17,7 +17,7 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
     process_sql(ActiveRecord::Base, "SELECT 1 FROM projects")
   end
 
-  context 'properly observes all queries', :add_ci_connection do
+  context 'properly observes all queries', :add_ci_connection, :request_store do
     using RSpec::Parameterized::TableSyntax
 
     where do
@@ -28,7 +28,8 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
           expectations: {
             gitlab_schemas: "gitlab_main",
             db_config_name: "main"
-          }
+          },
+          setup: nil
         },
         "for query accessing gitlab_ci and gitlab_main" => {
           model: ApplicationRecord,
@@ -36,7 +37,8 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
           expectations: {
             gitlab_schemas: "gitlab_ci,gitlab_main",
             db_config_name: "main"
-          }
+          },
+          setup: nil
         },
         "for query accessing gitlab_ci and gitlab_main the gitlab_schemas is always ordered" => {
           model: ApplicationRecord,
@@ -44,7 +46,8 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
           expectations: {
             gitlab_schemas: "gitlab_ci,gitlab_main",
             db_config_name: "main"
-          }
+          },
+          setup: nil
         },
         "for query accessing CI database" => {
           model: Ci::ApplicationRecord,
@@ -53,6 +56,62 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
             gitlab_schemas: "gitlab_ci",
             db_config_name: "ci"
           }
+        },
+        "for query accessing CI database with re-use and disabled sharing" => {
+          model: Ci::ApplicationRecord,
+          sql: "SELECT 1 FROM ci_builds",
+          expectations: {
+            gitlab_schemas: "gitlab_ci",
+            db_config_name: "ci",
+            ci_dedicated_primary_connection: true
+          },
+          setup: ->(_) do
+            skip_if_multiple_databases_not_setup
+            stub_env('GITLAB_LOAD_BALANCING_REUSE_PRIMARY_ci', 'main')
+            stub_feature_flags(force_no_sharing_primary_model: true)
+          end
+        },
+        "for query accessing CI database with re-use and enabled sharing" => {
+          model: Ci::ApplicationRecord,
+          sql: "SELECT 1 FROM ci_builds",
+          expectations: {
+            gitlab_schemas: "gitlab_ci",
+            db_config_name: "ci",
+            ci_dedicated_primary_connection: false
+          },
+          setup: ->(_) do
+            skip_if_multiple_databases_not_setup
+            stub_env('GITLAB_LOAD_BALANCING_REUSE_PRIMARY_ci', 'main')
+            stub_feature_flags(force_no_sharing_primary_model: false)
+          end
+        },
+        "for query accessing CI database without re-use and disabled sharing" => {
+          model: Ci::ApplicationRecord,
+          sql: "SELECT 1 FROM ci_builds",
+          expectations: {
+            gitlab_schemas: "gitlab_ci",
+            db_config_name: "ci",
+            ci_dedicated_primary_connection: true
+          },
+          setup: ->(_) do
+            skip_if_multiple_databases_not_setup
+            stub_env('GITLAB_LOAD_BALANCING_REUSE_PRIMARY_ci', nil)
+            stub_feature_flags(force_no_sharing_primary_model: true)
+          end
+        },
+        "for query accessing CI database without re-use and enabled sharing" => {
+          model: Ci::ApplicationRecord,
+          sql: "SELECT 1 FROM ci_builds",
+          expectations: {
+            gitlab_schemas: "gitlab_ci",
+            db_config_name: "ci",
+            ci_dedicated_primary_connection: true
+          },
+          setup: ->(_) do
+            skip_if_multiple_databases_not_setup
+            stub_env('GITLAB_LOAD_BALANCING_REUSE_PRIMARY_ci', nil)
+            stub_feature_flags(force_no_sharing_primary_model: false)
+          end
         }
       }
     end
@@ -63,8 +122,15 @@ RSpec.describe Gitlab::Database::QueryAnalyzers::GitlabSchemasMetrics, query_ana
       end
 
       it do
+        stub_env('GITLAB_LOAD_BALANCING_REUSE_PRIMARY_ci', nil)
+
+        instance_eval(&setup) if setup
+
+        allow(::Ci::ApplicationRecord.load_balancer).to receive(:configuration)
+          .and_return(Gitlab::Database::LoadBalancing::Configuration.for_model(::Ci::ApplicationRecord))
+
         expect(described_class.schemas_metrics).to receive(:increment)
-          .with(expectations).and_call_original
+          .with({ ci_dedicated_primary_connection: anything }.merge(expectations)).and_call_original
 
         process_sql(model, sql)
       end