Replace lua with luajit

[xiaobiaozhao]

Luajit has better performance and I think luajit can be used instead of Lua

Luajit official performance report
https://luajit.org/performance_x86.html

luajit vs c
https://mp.weixin.qq.com/s/MDTb9SSkdnOm5VIMEjA9QA

1. If use luajit insteand of lua，kvrocks can run a lua scripte in db side.
2. If lua scripte has high performance，user can move some logic to kvrocks, less network traffic betten db and client.

[git-hulk]

@tisonkun proposed this in another thread but the only concern is
that will break the consistency with Redis(Lua 5.1).

[tisonkun]

LuaJIT claims that it's compatible with Lua 5.1 but we must have some test coverage to confidently make the change.

[git-hulk]

Cool, I didn't notice LuaJIT is compatible with Lua 5.1. If so, I think we can have
a try if @xiaobiaozhao willing to do that. I will be happy to be involved in testing
the compatibility and functionality.

[PragmaTwice]

I think this idea is amazing, although some investigation is needed:

• does the API of luajit have a huge difference than lua?
• does luajit have something equal to lua-cjson (or other in-use lua extension)?
• redis did some change to the original lua codebase, could we transplant it to luajit?

[PragmaTwice]

I have make a kvrocks demo with luajit. It works well.

• luajit and lua5.1 have same api
• lua-cjson works well on luajit
• As far as I know, Redis hasn't changed Lua, just added some Lua extensions that can be ported to Luajit

You can check here: https://github.com/redis/redis/commits/unstable/deps/lua/src
They did some changes to lua codebases, not only lua extensions (they also modified some logic in lua extensions).
And some issues in lua-cjson with luajit: mpx/lua-cjson#40.

[PragmaTwice]

I mean, I'm really looking forward to this change, but this change might be more complicated than expected, so it needs more work.

[xiaobiaozhao]

I've already done that

[PragmaTwice]

I've already done that

That is amazing! Look forward to your PR. 🥰

[xiaobiaozhao]

Here is my PR with luajit replace lua on my fork.

xiaobiaozhao#1

[ShooterIT]

Some redis issue or PR, FYI
redis/redis#7382
redis/redis#8180

[ShooterIT]

+1, go ahead