[Dovecot] expire plugin: columns not uniq

[Timo Sirainen]

On Mon, 2009-08-24 at 13:27 -0400, Timo Sirainen wrote:
> > CREATE TRIGGER mergeexpire BEFORE INSERT ON expires FOR EACH ROW
> > BEGIN 
> > 	UPDATE expires SET expire_stamp=NEW.expire_stamp 
> > 		WHERE username = NEW.username AND mailbox = NEW.mailbox; 
> > 	SELECT raise(ignore) 
> > 		WHERE (SELECT 1 FROM expires WHERE username = NEW.username AND mailbox = NEW.mailbox) IS NOT NULL;
> > END;
> > 
> > This seem some kind crudely to me, but it's working.
> 
> That looks correct to me. 

Oh, except there's a small race condition if the first row is being
added at the same time by two processes. That's why the PostgreSQL
trigger is so much more complex. But it should be somewhat rare I
guess..

Unless SQLite has some locks that prevent that? Anyway I was thinking
that two processes run the UPDATE part of the trigger and then both try
to INSERT. One of them succeeds and the other one fails. But the row
gets added anyway and the timestamp is the same anyway, so it probably
doesn't matter all that much, just logs an error.
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