presto-main/src/main/java/io/prestosql/execution/QueryTracker.java/QueryTracker/start
class QueryTracker:    public synchronized void start()
    {
        checkState(backgroundTask == null, "QueryTracker already started");
        backgroundTask = queryManagementExecutor.scheduleWithFixedDelay(() -> {
            try {
                failAbandonedQueries();
            }
            catch (Throwable e) {
                log.error(e, "Error cancelling abandoned queries");
            }

            try {
                enforceTimeLimits();
            }
            catch (Throwable e) {
                log.error(e, "Error enforcing query timeout limits");
            }

            try {
                removeExpiredQueries();
            }
            catch (Throwable e) {
                log.error(e, "Error removing expired queries");
            }

            try {
                pruneExpiredQueries();
            }
            catch (Throwable e) {
                log.error(e, "Error pruning expired queries");
            }
        }, 1, 1, TimeUnit.SECONDS);
    }