> On 3/21/07, Warren Little <[EMAIL PROTECTED]> wrote: > >> Also, is there a guide to configuring Slony-I on an active system, or is >> the >> procedure the same (aside for the standard "backup all data before you >> begin") > > You may want to schedule a brief maintenance window when initially > adding tables since it requires an exclusive lock. Which is part of > the standard procedures, however I thought I'd mention it specifically > to make sure you don't miss it.
There's a difference between the locking for this and other locking; the SET ADD TABLE action requires a brief exclusive lock to attach the replication trigger to each table. Unlike behaviour on subscribers, where there winds up being one grand transaction requiring exclusive locks on ALL the replicated tables, all at once, the actions initially on the master are (hopefully) brief, and go individually, table by table. If you have processes on the master database that hold lots of locks, this can bite you. If you don't have heavy locking going on there, SET ADD TABLE may be able to slip through fairly trouble-free alongside the other traffic. We've frequently been able to add new tables (not yet used by the application) on the fly while application users are connected. Tables that are thus far unused will be pretty easy on locking. It's less clear what'll happen with busy tables that are widely used. In such a case, it's entirely possible for there to be a few seconds of pause as the request for the exclusive lock blocks everything that comes in behind it, but still has to wait until all the requests that came in before it clear their way through. Whether that's milliseconds or seconds or more depends on the usage pattern... _______________________________________________ Slony1-general mailing list [email protected] http://lists.slony.info/mailman/listinfo/slony1-general
