[Pgpool-general] PgPool and sequences

Pascal Cohen pcohen at wimba.com
Sun Dec 2 09:44:37 UTC 2007


Hello, I have read in the documentation that there is no guarantee that 
sequence may have the same value on all servers.

This is not perhaps not very probable (theoretical) but could such a 
following situation occur:

I have two servers replicated and I want to add in a users table (id, 
name) with a sequence users_seq, two users A and B:

First connection sends to PgPool: INSERT INTO USERS VALUES 
(next_val('users_seq'),'A');  -- ReqA
At the same time a second connection sends to PgPool: INSERT INTO USERS 
VALUES (next_val('users_seq'),'B'); -- ReqB

Could we have something like:
- On Server 1:
1 A
2 B
- On server 2:
1 B
2 A

I mean updates are not sent in the same order to all servers for any 
reason (several CPUs on server handling the request slower, or anything 
else). Is that possible ?

Thanks

Pascal


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