On Mon, Mar 8, 2021 at 5:58 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > > Magnus Hagander <mag...@hagander.net> writes: > > On Mon, Mar 8, 2021 at 5:33 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > >> It does seem that --single-transaction is a better idea than fiddling with > >> the transaction wraparound parameters, since the latter is just going to > >> put off the onset of trouble. However, we'd have to do something about > >> the lock consumption. Would it be sane to have the backend not bother to > >> take any locks in binary-upgrade mode? > > > I believe the problem occurs when writing them rather than when > > reading them, and I don't think we have a binary upgrade mode there. > > You're confusing pg_dump's --binary-upgrade switch (indeed applied on > the dumping side) with the backend's -b switch (IsBinaryUpgrade, > applied on the restoring side).
Ah. Yes, I am. > > We could invent one of course. Another option might be to exclusively > > lock pg_largeobject, and just say that if you do that, we don't have > > to lock the individual objects (ever)? > > What was in the back of my mind is that we've sometimes seen complaints > about too many locks needed to dump or restore a database with $MANY > tables; so the large-object case seems like just a special case. It is -- but I guess it's more likely to have 100M large objects than to have 100M tables. (and the cutoff point comes a lot earlier than 100M). But the fundamental onei s the same. > The answer up to now has been "raise max_locks_per_transaction enough > so you don't see the failure". Having now consumed a little more > caffeine, I remember that that works in pg_upgrade scenarios too, > since the user can fiddle with the target cluster's postgresql.conf > before starting pg_upgrade. > > So it seems like the path of least resistance is > > (a) make pg_upgrade use --single-transaction when calling pg_restore > > (b) document (better) how to get around too-many-locks failures. Agreed. Certainly seems like a better path forward than arbitrarily pushing the limit on number of transactions which just postpones the problem. -- Magnus Hagander Me: https://www.hagander.net/ Work: https://www.redpill-linpro.com/
