Initie une bascule de log si aucune n'est déjà en cours.

DECLARE
        v_current_status        int4;
BEGIN
        -- ----
        -- Grab the central configuration lock to prevent race conditions
        -- while changing the sl_log_status sequence value.
        -- ----
        lock table sl_config_lock;

        -- ----
        -- Get the current log status.
        -- ----
        select last_value into v_current_status from sl_log_status;

        -- ----
        -- status = 0: sl_log_1 active, sl_log_2 clean
        -- Initiate a switch to sl_log_2.
        -- ----
        if v_current_status = 0 then
                perform "pg_catalog".setval('sl_log_status', 3);
                perform registry_set_timestamp(
                                'logswitch.laststart', now()::timestamp);
                raise notice 'Slony-I: Logswitch to sl_log_2 initiated';
                return 2;
        end if;

        -- ----
        -- status = 1: sl_log_2 active, sl_log_1 clean
        -- Initiate a switch to sl_log_1.
        -- ----
        if v_current_status = 1 then
                perform "pg_catalog".setval('sl_log_status', 2);
                perform registry_set_timestamp(
                                'logswitch.laststart', now()::timestamp);
                raise notice 'Slony-I: Logswitch to sl_log_1 initiated';
                return 1;
        end if;

        raise exception 'Previous logswitch still in progress';
END;