Weird procedure question - Mailing list pgsql-general

Hi all,

   I've got an interesting use case that I am stuck on. It's a bit of a
complicated environment, but I'll try to keep it simple.

   In short; I have a history schema that has tables that match the
public schema, plus one 'history_id' column that has a simple sequential
bigserial value. Then I have a procedure and trigger that, on UPDATE or
INSERT, copies the data to history. Example use case is that I can
UPDATE a sensor value in the public table and it's also INSERTs the data
into history. So public shows just the most recent values, but I can see
changes over time in the history schema.

   I have built my system to support writing to one or more DBs. I keep
a list of connected DBs and send INSERT/UPDATE calls to a method that
then runs the UPDATE/INSERT against all connected databases, as a form
of redundancy. This all works fine.

   The problem I've hit is that the 'history_id' differs between the
various databases. So I want to switch this to 'history_uuid' and use
UUIDs instead of bigserial.

   Now the question;

   Can I tell a produce to use a specific UUID?

   The idea is to generate a UUID for 'history_uuid' so that I have
consistency across databases. Of course, if an UPDATE will change
multiple rows, then I'll need to predefine multiple UUIDs. This is where
things start to get really complicated I think... Maybe I could pass an
array of UUIDs? I don't care if I find out which UUID was used for which
record, just that the same UUID was used for the same record when the
procedure is (re)run on other DBs.

   The databases are not clustered, on purpose. I've been trying to
handle all the HA stuff in my application for various reasons.

If it helps, here is an example pair of tables, the procedure and the
trigger I currently use;

====
CREATE TABLE host_variable (
     host_variable_uuid uuid                        not null    primary key,
     host_variable_host_uuid    uuid                        not null,
     host_variable_name text                        not null,
     host_variable_value text                        not null,
     modified_date              timestamp with time zone    not null
);
ALTER TABLE host_variable OWNER TO admin;

CREATE TABLE history.host_variable (
     history_id                 bigserial,
     host_variable_uuid         uuid,
     host_variable_host_uuid    uuid,
     host_variable_name         text,
     host_variable_value        text,
     modified_date              timestamp with time zone    not null
);
ALTER TABLE history.host_variable OWNER TO admin;

CREATE FUNCTION history_host_variable() RETURNS trigger
AS $$
DECLARE
     history_host_variable RECORD;
BEGIN
     SELECT INTO history_host_variable * FROM host_variable WHERE
host_uuid = new.host_uuid;
     INSERT INTO history.host_variable
         (host_variable_uuid,
          host_variable_host_uuid,
          host_variable_name,
          host_variable_value,
          modified_date)
     VALUES
         (history_host_variable.host_variable_uuid,
          history_host_variable.host_variable_host_uuid,
          history_host_variable.host_variable_name,
          history_host_variable.host_variable_value,
          history_host_variable.modified_date);
     RETURN NULL;
END;
$$
LANGUAGE plpgsql;
ALTER FUNCTION history_host_variable() OWNER TO admin;

CREATE TRIGGER trigger_host_variable
     AFTER INSERT OR UPDATE ON host_variable
     FOR EACH ROW EXECUTE PROCEDURE history_host_variable();
====

   I know this might sound odd, but I didn't want to complicate things
with how my system works. However, if it would help solve the problem,
I'm happy to dig into more detail.

   Thanks!