1 files changed, 71 insertions, 0 deletions
diff --git a/lib/gitlab/database/health_status/indicators/write_ahead_log.rb b/lib/gitlab/database/health_status/indicators/write_ahead_log.rb
new file mode 100644
index 00000000000..1614b17df48
--- /dev/null
+++ b/lib/gitlab/database/health_status/indicators/write_ahead_log.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module HealthStatus
+      module Indicators
+        class WriteAheadLog
+          include Gitlab::Utils::StrongMemoize
+
+          LIMIT = 42
+          PENDING_WAL_COUNT_SQL = <<~SQL
+            WITH
+            current_wal_file AS (
+              SELECT pg_walfile_name(pg_current_wal_insert_lsn()) AS pg_walfile_name
+            ),
+            current_wal AS (
+              SELECT
+                ('x' || substring(pg_walfile_name, 9, 8))::bit(32)::int AS log,
+                ('x' || substring(pg_walfile_name, 17, 8))::bit(32)::int AS seg,
+                pg_walfile_name
+              FROM current_wal_file
+            ),
+            archive_wal AS (
+              SELECT
+                ('x' || substring(last_archived_wal, 9, 8))::bit(32)::int AS log,
+                ('x' || substring(last_archived_wal, 17, 8))::bit(32)::int AS seg,
+                last_archived_wal
+              FROM pg_stat_archiver
+            )
+            SELECT ((current_wal.log - archive_wal.log) * 256) + (current_wal.seg - archive_wal.seg) AS pending_wal_count
+            FROM current_wal, archive_wal
+          SQL
+
+          def initialize(context)
+            @connection = context.connection
+          end
+
+          def evaluate
+            return Signals::NotAvailable.new(self.class, reason: 'indicator disabled') unless enabled?
+
+            unless pending_wal_count
+              return Signals::NotAvailable.new(self.class, reason: 'WAL archive queue can not be calculated')
+            end
+
+            if pending_wal_count > LIMIT
+              Signals::Stop.new(self.class, reason: "WAL archive queue is too big")
+            else
+              Signals::Normal.new(self.class, reason: 'WAL archive queue is within limit')
+            end
+          end
+
+          private
+
+          attr_reader :connection
+
+          def enabled?
+            Feature.enabled?(:batched_migrations_health_status_wal, type: :ops)
+          end
+
+          # Returns number of WAL segments pending archival
+          def pending_wal_count
+            Gitlab::Database::LoadBalancing::Session.current.use_primary do
+              connection.execute(PENDING_WAL_COUNT_SQL).to_a.first&.fetch('pending_wal_count')
+            end
+          end
+          strong_memoize_attr :pending_wal_count
+        end
+      end
+    end
+  end
+end