On 2016-06-23 18:59:57 -0400, Alvaro Herrera wrote: > Andres Freund wrote: > > > I'm looking into three approaches right now: > > > > 3) Use WAL logging for the already_marked = true case. > > > > 3) This approach so far seems the best. It's possible to reuse the > > xl_heap_lock record (in an afaics backwards compatible manner), and in > > most cases the overhead isn't that large. It's of course annoying to > > emit more WAL, but it's not that big an overhead compared to extending a > > file, or to toasting. It's also by far the simplest fix. > > I suppose it's fine if we crash midway from emitting this wal record and > the actual heap_update one, since the xmax will appear to come from an > aborted xid, right?
Yea, that should be fine. > I agree that the overhead is probably negligible, considering that this > only happens when toast is invoked. It's probably not as great when the > new tuple goes to another page, though. I think it has to happen in both cases unfortunately. We could try to add some optimizations (e.g. only release lock & WAL log if the target page, via fsm, is before the current one), but I don't really want to go there in the back branches. Andres -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers