Function db_data_version_incr

db/exec.c:104–119

By making the update conditional on the current value we expect we * are implementing an optimistic lock: if the update results in * changes on the DB we know that the data_version did not change * under our feet and no other transaction ran in the meantime. * * Notice that this update effectively locks the row, so that other * operations attempting to change this outside the transaction wil

 * until our transaction is committed.
 */
static void db_data_version_incr(struct db *db)
{
       struct db_stmt *stmt = db_prepare_v2(
	       db, SQL("UPDATE vars "
		       "SET intval = intval + 1 "
		       "WHERE name = 'data_version'"
		       " AND intval = ?"));
       db_bind_int(stmt, 0, db->data_version);
       db_exec_prepared_v2(stmt);
       if (db_count_changes(stmt) != 1)
	       db_fatal("Optimistic lock on the database failed. There"
			" may be a concurrent access to the database."
			" Aborting since concurrent access is unsafe.");
       tal_free(stmt);
       db->data_version++;
}

void db_begin_transaction_(struct db *db, const char *location)
{