Andres Freund <and...@2ndquadrant.com> writes: > On 2012-12-06 18:42:22 +0000, Simon Riggs wrote: >> "in-between state" means what? And what danger do you see? > > For example during table rewrites we have a temporary pg_class entry > thats a full copy of the table, with a separate oid, relfilenode and > everything. That gets dropped rather unceremonially, without the usual > safety checks. If the user did anything referencing that table we would > possibly have a corrupt catalog or even a segfault at our hands. > > For normal triggers the code takes quite some care to avoid such > dangers.
I think we need to be solving that problem when we implement new firing points for event trigger. The 'table_rewrite' event needs to fire at a time when the code can cope with it. That's the main difficulty in adding events in that system, asserting their code location safety. > Event triggers get called *during* the ALTER TABLE. So if were not > careful they see something thats not easy to handle. They need to fire before catalogs are modified, or after, not in between, I agree with that. I don't see other ways of implementing that than carefully placing the call to user code in the backend's code. > I am for example not sure what would happen if we had a "rewrite" event > trigger which inserts a log entry into a logtable. Not a stupid idea, > right? > Now imagine we had a deferred unique key on that logtable and the > logtable is the one that gets rewritten... The log insert needs to happen either before or after the rewrite, in terms of catalog state. I don't see any magic bullet here. -- Dimitri Fontaine http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
