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-- ----------
-- txid.sql
--
-- SQL script for loading the transaction ID compatible datatype
--
-- Copyright (c) 2003-2004, PostgreSQL Global Development Group
-- Author: Jan Wieck, Afilias USA INC.
--
-- ----------
--
-- now the epoch storage
--
CREATE SCHEMA txid;
-- remember txid settings
-- use bigint so we can do arithmetic with it
create table txid.epoch (
epoch bigint,
last_value bigint
);
-- make sure there exist exactly one row
insert into txid.epoch values (0, 1);
-- then protect it
create function txid.epoch_guard()
returns trigger as $$
begin
if TG_OP = 'UPDATE' then
-- epoch: allow only small increase
if NEW.epoch > OLD.epoch and NEW.epoch < (OLD.epoch + 3) then
return NEW;
end if;
-- last_value: allow only increase
if NEW.epoch = OLD.epoch and NEW.last_value > OLD.last_value then
return NEW;
end if;
end if;
raise exception 'bad operation on txid.epoch';
end;
$$ language plpgsql;
-- the trigger
create trigger epoch_guard_trigger
before insert or update or delete on txid.epoch
for each row execute procedure txid.epoch_guard();
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