send alert for transaction wraparound

migrate/20240619_lantern_doctor_queries.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+Sequel.migration do
+  up do
+    # percent toward transaction wraparound
+    sql = <<SQL
+ SELECT 2000000000 as max_old_xid,
+        setting AS autovacuum_freeze_max_age
+        FROM pg_catalog.pg_settings
+        WHERE name = 'autovacuum_freeze_max_age')
+, per_database_stats AS (
+    SELECT datname
+        , m.max_old_xid::int
+        , m.autovacuum_freeze_max_age::int
+        , age(d.datfrozenxid) AS oldest_current_xid
+    FROM pg_catalog.pg_database d
+    JOIN max_age m ON (true)
+    WHERE d.datallowconn )
+SELECT max(ROUND(100*(oldest_current_xid/max_old_xid::float))) > 85 FROM per_database_stats;
+SQL
+    DB[:lantern_doctor_query].insert(
+      id: "98cf148c-a88c-85b7-9bec-dbc912b022be",
+      name: "Percent towards tx wraparound is >85%",
+      db_name: "postgres",
+      schedule: "45 */10 * * *",
+      condition: "unknown",
+      sql: sql,
+      type: "system",
+      response_type: "bool",
+      severity: "warning"
+    )
+  end
+end

model/lantern/lantern_doctor_query.rb

@@ -169,6 +169,7 @@ def check_disk_space_usage(_db, _query_user)
         server_type = serv.primary? ? "primary" : "standby"
         output += "#{server_type} server - usage #{usage_percent}%\n"
       end
+    rescue
     end
     output.chomp
   end