On Sat, Mar 9, 2019 at 7:58 PM Andrew Dunstan <andrew.duns...@2ndquadrant.com> wrote: > > On 3/9/19 12:55 PM, Tom Lane wrote: > >> Maybe we could leave the default units as msec but store it and allow > >> specifying as usec. Not sure how well the GUC mechanism would cope with > >> that. > > I took a quick look at that and I'm afraid it'd be a mess. GUC doesn't > > really distinguish between a variable's storage unit, its default input > > unit, or its default output unit (as seen in e.g. pg_settings). Perhaps > > we could split those into two or three distinct concepts, but it seems > > complicated and bug-prone. Also I think we'd still be forced into > > making obviously-incompatible changes in what pg_settings shows for > > this variable, since what it shows right now is integer ms. That last > > isn't a deal-breaker perhaps, but 100% compatibility isn't going to > > happen this way. > > > > The idea of converting vacuum_cost_delay into a float variable, while > > keeping its native unit as ms, seems probably more feasible from a > > compatibility standpoint. There are two sub-possibilities: > > > > 1. Just do that and lose units support for the variable. I don't > > think this is totally unreasonable, because up to now ms is the > > *only* workable unit for it: > > > > regression=# set vacuum_cost_delay = '1s'; > > ERROR: 1000 is outside the valid range for parameter "vacuum_cost_delay" > > (0 .. 100) > > > > Still, it'd mean that anyone who'd been explicitly setting it with > > an "ms" qualifier would have to change their postgresql.conf entry. > > > > 2. Add support for units for float variables, too. I don't think > > this'd be a huge amount of work, and we'd surely have other uses > > for it in the long run. > > > > I'm inclined to go look into #2. Anybody think this is a bad idea? > > Sounds good to me, seems much more likely to be future-proof.
Agreed.
