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

[Igor Munkin <imun@tarantool.org>]

Olya,

Thanks for the patch!

On 29.06.20, Olga Arkhangelskaia wrote:
> The patch fixes the output of box.info:memory(). It used to return the same
> table as the box.info().
> 
> box.info.memory() can be written as box.info[“memory”](), that later has the only
> one argument on the stack - box.info.memory table we need to fill:
> box.info.memory() -> getmetatable(box.info.memory).__call(box.info.memory)[1]
> box.info:memory() call is the same as box.info[“memory”](box.info). So, it
> results in extra argument on the stack[1].
> box.info:mem()->getmetatable(box.info.memory).__call(box.info.memory, box.info).
> When function tries to fill box.info table - __call metamethod of box.info is
> trigged - resulting in box.info table returned as the result.

Nice passage! I guess it should be polished an added to the original
commit message.

> 
> There are two options to get rid if extra box.info table:
> 1. Create new table in the beginning of the function(eg. box.info.gc).
> Every time box.info.memory is called it will generate new table with the fresh
> info.
> 2. The second way is to ignore box.info argument on the stack and fill
> directly box.info.memory table, that was passed as an argument.
> 
> I have implemented the first approach because there is box.info.gc works
> the same way and we only need to add one line of code.
> However, I do not know why it was done in such a way on the first place.
> So if you have pros for the second options, please share with me.

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.

> 
> [1] https://www.lua.org/manual/5.1/manual.html#2.8
> 
> @Changelog:
> To retrieve information about memory usage box.info:memory() can be used.
> Olga Arkhangelskaia (1):
>   box: fixed box.info:memory()
> 
>  src/box/lua/info.c                            |  1 +
>  test/box-tap/gh-4668-box-info-memory.test.lua | 15 +++++++++++++++
>  2 files changed, 16 insertions(+)
>  create mode 100755 test/box-tap/gh-4668-box-info-memory.test.lua
> 
> -- 
> 2.20.1 (Apple Git-117)
> 

-- 
Best regards,
IM