Better migration locking behaviour

sql/migrations/create.sql

@@ -2,4 +2,12 @@ CREATE TABLE IF NOT EXISTS migrations (
     id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
     name text UNIQUE NOT NULL,
     applied_at timestamptz NOT NULL DEFAULT CURRENT_TIMESTAMP
-)
+);
+
+CREATE TABLE IF NOT EXISTS migrations_lock (
+    id integer PRIMARY KEY,
+    is_locked boolean NOT NULL DEFAULT false
+);
+
+INSERT INTO migrations_lock (id, is_locked) VALUES (1, false) 
+    ON CONFLICT DO NOTHING;

sql/migrations/lock.sql

@@ -0,0 +1,3 @@
+WITH rows as (
+    UPDATE migrations_lock SET is_locked = true WHERE is_locked = false RETURNING 1
+) SELECT COUNT(*) FROM rows;

sql/migrations/unlock.sql

@@ -0,0 +1 @@
+UPDATE migrations_lock SET is_locked = false WHERE is_locked = true;