Re: [Tarantool-patches] [PATCH] Move txn from shema to a separate module (use C API instead of FFI)

[Igor Munkin <imun@tarantool.org>]

Kostja,

On 29.11.19, Konstantin Osipov wrote:
> * Igor Munkin <imun@tarantool.org> [19/11/28 21:39]:
> 
> > Great, we discussed with Leonid and Sasha offline and agreed to make
> > several benchmarks to be provided in this thread. With no benchmarks all
> > our estimates can be simply wrong.
> 
> For benchmarks, it is always good to refresh them but since you've
> been working with LuaJIT for a while you must know some of 
> the conclusions already:
> 
> * JITed code can be 5-8x faster than Lua + Lua/C
> * FFI is 1.5-2x slower than Lua/C in non-JIT mode. So using FFI
>   is an extra cost if JIT is OFF.
> * The way traces are collected, cached and stored has its own
>   overhead, so JIT ON can be harmful to performance if Lua code
>   base gets big.

Additionally, enabling JIT can nerf performance on a heterogeneous data
considering the guarded *LOADs.

I can confirm nothing for the numbers you've written above. There are
several benchmarks for LuaJIT itself regarding a different workload. My
point was about benchmarks for LuaJIT within Tarantool, since we are
going to tune it for Tarantool environment primarily.

> 
> In practice, for Tarantool apps, I found all of the above to not
> have much impact. The #1 cause of performance slowdown in
> Tarantool apps is boxing/unboxing Tarantool tuples and garbage
> collection.
> 
> So to measure the real impact of the change, micro-benchmarking
> is insufficient. One has to use run e.g. vshard or data
> grid or other complex app stress test with wal_mode=off to 
> see the effect of such change.
> 
> -- 
> Konstantin Osipov, Moscow, Russia

-- 
Best regards,
IM