Re: [Tarantool-patches] [PATCH 0/1] fix box.info:memory()

[Alexander Turenko <alexander.turenko@tarantool.org>]

> > > I have no idea why it is implemented in such complex way, maybe Sasha
> > > does? Why box.info.memory yields an empty "callable" table on each
> > > lookup? Why it can't just return a function to be called or a table with
> > > memory metrics as a result of the lookup? Unfortunately the latter
> > > approach breaks the backward compatibility but the first one can save
> > > some time on short-term objects creation (I guess no one checks
> > > box.info.memory type). Thoughts? Please also consider the comments I
> > > left for the patch itself.
> > 
> > I don't see a reason. The history of src/box/lua/info.c changes shows
> > that this way was initially implemented for box.info.phia() (which was
> > renamed later to box.info.vinyl()). Then box.info.memory(),
> > box.info.gc() and box.info.sql() were added in the same way.
> > box.info.phia() was moved from box.phia().
> > 
> > I agree with you. We should define a case to estimate impact of
> > replacing a table + metamethod with a function. Not even to make a
> > decision whether it worth to change, but to imagine the situation at
> > whole.
> > 
> > I would consider metrics collection case using tarantool/metrics every
> > minute when default metrics are enabled. I guess it'll call
> > box.info.vinyl(), box.info.memory() and box.info.gc() once for each
> > metrics collection. So the proposed change will safe 3 extra short-term
> > object creations per minute.
> > 
> > I don't see a case when those functions should be called more often and
> > become a part of hot path. So I would say that reducing of GC object
> > allocations here does not look worthful for me considering possible
> > impact of subtle differences (like serialization of `box.info` or other
> > differences we can miss) that may fail some scripts or tools.
> 
> Yes, it's definitely not a part of the hot path, *but* still implicitly
> affects the platform performance a little. Maybe we need to file an
> issue for such investigation? It would be nice to look on this part
> under the particular workload.

I would take it with a little priority, but of course I don't have
objections against filing an issue if you see an area for improvement.