Change to db_config.name for logging metrics per database

As GitLab is planning on moving `ci_*` tables to a separate database we
need to start expanding our observability/logging/metrics to allow us to
distinguish between the different databases being queried.

We had already implemented logging per database by including the
database name (ie. what Postgres calls the database) in the log
statements in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63490 but later we
learnt this wasn't a good idea because we may want to use 2 different
Postgres servers with the same Database name (in fact that's what our
current migration plan involves). As such we need to use the name that
the GitLab application uses to distinguish between the 2 different
databases. This is the name used to configure the `config/database.yml`
and must be unique.

In the default case it does not have a name and Rails will call it
`primary`. This has the unfortunate result that this MR will add JSON
log keys `db_replica_primary_duration_s` and
`db_primary_primary_duration_s` because we already use the words
`primary/replica` to distinguish between our read-write primary and
read-only replicas. We plan to eventually force the
`config/database.yml` to name these `main` and `ci` and at that time
these log statements will be a little clearer. In the meantime this is
behind a feature flag so should not bother people that aren't intending
to try and make sense of these metrics.

lib/gitlab/database.rb

@@ -352,11 +352,11 @@ module Gitlab
       end
     end
 
-    def self.dbname(ar_connection)
+    def self.db_config_name(ar_connection)
       if ar_connection.respond_to?(:pool) &&
           ar_connection.pool.respond_to?(:db_config) &&
-          ar_connection.pool.db_config.respond_to?(:database)
-        return ar_connection.pool.db_config.database
+          ar_connection.pool.db_config.respond_to?(:name)
+        return ar_connection.pool.db_config.name
       end
 
       'unknown'

lib/gitlab/metrics/subscribers/active_record.rb

@@ -74,9 +74,9 @@ module Gitlab
               end
 
               if Feature.enabled?(:multiple_database_metrics, default_enabled: :yaml)
-                ::Gitlab::SafeRequestStore[:duration_by_database]&.each do |dbname, duration_by_role|
+                ::Gitlab::SafeRequestStore[:duration_by_database]&.each do |name, duration_by_role|
                   duration_by_role.each do |db_role, duration|
-                    payload[:"db_#{db_role}_#{dbname}_duration_s"] = duration.to_f.round(3)
+                    payload[:"db_#{db_role}_#{name}_duration_s"] = duration.to_f.round(3)
                   end
                 end
               end
@@ -113,11 +113,11 @@ module Gitlab
           ::Gitlab::SafeRequestStore[duration_key] = (::Gitlab::SafeRequestStore[duration_key].presence || 0) + duration
 
           # Per database metrics
-          dbname = ::Gitlab::Database.dbname(event.payload[:connection])
+          name = ::Gitlab::Database.db_config_name(event.payload[:connection])
           ::Gitlab::SafeRequestStore[:duration_by_database] ||= {}
-          ::Gitlab::SafeRequestStore[:duration_by_database][dbname] ||= {}
-          ::Gitlab::SafeRequestStore[:duration_by_database][dbname][db_role] ||= 0
-          ::Gitlab::SafeRequestStore[:duration_by_database][dbname][db_role] += duration
+          ::Gitlab::SafeRequestStore[:duration_by_database][name] ||= {}
+          ::Gitlab::SafeRequestStore[:duration_by_database][name][db_role] ||= 0
+          ::Gitlab::SafeRequestStore[:duration_by_database][name][db_role] += duration
         end
 
         def ignored_query?(payload)

spec/lib/gitlab/database_spec.rb

@@ -487,19 +487,19 @@ RSpec.describe Gitlab::Database do
     end
   end
 
-  describe '.dbname' do
-    it 'returns the dbname for the connection' do
+  describe '.db_config_name' do
+    it 'returns the db_config name for the connection' do
       connection = ActiveRecord::Base.connection
 
-      expect(described_class.dbname(connection)).to be_a(String)
-      expect(described_class.dbname(connection)).to eq(connection.pool.db_config.database)
+      expect(described_class.db_config_name(connection)).to be_a(String)
+      expect(described_class.db_config_name(connection)).to eq(connection.pool.db_config.name)
     end
 
     context 'when the pool is a NullPool' do
       it 'returns unknown' do
         connection = double(:active_record_connection, pool: ActiveRecord::ConnectionAdapters::NullPool.new)
 
-        expect(described_class.dbname(connection)).to eq('unknown')
+        expect(described_class.db_config_name(connection)).to eq('unknown')
       end
     end
   end

spec/lib/gitlab/sidekiq_logging/structured_logger_spec.rb

@@ -298,7 +298,7 @@ RSpec.describe Gitlab::SidekiqLogging::StructuredLogger do
           allow(Gitlab::Database::LoadBalancing).to receive(:enable?).and_return(true)
         end
 
-        let(:dbname) { ::Gitlab::Database.dbname(ActiveRecord::Base.connection) }
+        let(:db_config_name) { ::Gitlab::Database.db_config_name(ActiveRecord::Base.connection) }
 
         let(:expected_end_payload_with_db) do
           expected_end_payload.merge(
@@ -314,7 +314,7 @@ RSpec.describe Gitlab::SidekiqLogging::StructuredLogger do
             'db_primary_cached_count' => 0,
             'db_primary_wal_count' => 0,
             'db_primary_duration_s' => a_value > 0,
-            "db_primary_#{dbname}_duration_s" => a_value > 0,
+            "db_primary_#{db_config_name}_duration_s" => a_value > 0,
             'db_primary_wal_cached_count' => 0,
             'db_replica_wal_cached_count' => 0
           )

spec/support/shared_examples/metrics/active_record_subscriber_shared_examples.rb

@@ -23,7 +23,7 @@ RSpec.shared_examples 'store ActiveRecord info in RequestStore' do |db_role|
             db_replica_wal_cached_count: 0,
             db_replica_wal_count: 0
           }
-          expected[:"db_primary_#{::Gitlab::Database.dbname(connection)}_duration_s"] = 0.002 if record_query
+          expected[:"db_primary_#{::Gitlab::Database.db_config_name(connection)}_duration_s"] = 0.002 if record_query
         elsif db_role == :replica
           expected = {
             db_count: record_query ? 1 : 0,
@@ -40,7 +40,7 @@ RSpec.shared_examples 'store ActiveRecord info in RequestStore' do |db_role|
             db_primary_wal_cached_count: 0,
             db_primary_wal_count: 0
           }
-          expected[:"db_replica_#{::Gitlab::Database.dbname(connection)}_duration_s"] = 0.002 if record_query
+          expected[:"db_replica_#{::Gitlab::Database.db_config_name(connection)}_duration_s"] = 0.002 if record_query
         else
           expected = {
             db_count: record_query ? 1 : 0,
@@ -64,7 +64,7 @@ RSpec.shared_examples 'store ActiveRecord info in RequestStore' do |db_role|
         subscriber.sql(event)
         connection = event.payload[:connection]
 
-        expect(described_class.db_counter_payload).not_to include(:"db_replica_#{::Gitlab::Database.dbname(connection)}_duration_s")
+        expect(described_class.db_counter_payload).not_to include(:"db_replica_#{::Gitlab::Database.db_config_name(connection)}_duration_s")
       end
     end
   end