Redis eval vs Openresty lua script

fc28222 · 2013-10-28T03:54:47+00:00

Hello! On Sat, Oct 26, 2013 at 8:23 PM, Roberto Ostinelli wrote: > > I thought that require statements actually cached lua code (i.e. these get > p...

Redis eval vs Openresty lua script

fc28222

I am trying to write a custom lua-redis function that potential involved thousands of temporary variable (like getting the thousands of values from redis first and then do manipulation in lua).

So one can use the redis eval function to run such a script, or by using openresty, one can write the lua script that use lua-resty-redis.

In principle, which method should be preferred?

agentzh

Hello!

On Fri, Oct 25, 2013 at 11:50 PM,  <fc2...@gmail.com> wrote:
> I am trying to write a custom lua-redis function that potential involved
> thousands of temporary variable (like getting the thousands of values from
> redis first and then do manipulation in lua).
> So one can use the redis eval function to run such a script, or by using
> openresty, one can write the lua script that use lua-resty-redis.
> In principle, which method should be preferred?
>

It depends. Generally, in-redis Lua script should stay simple enough
to prevent blocking the single-threaded Redis server for too long.

Why not just compare two approaches yourself? :)

Best regards,
-agentzh

fc28222

Hello agentzh,

Thank a lot. I did try to test for speed myself, but I am not quite sure if I am using the right way since I am new to lua.

I used ngx.say(os.clock()) at the end of my lua script. Supposedly it is the whole run time of the lua script?

However how can I monitor the run time of a specific function inside a lua script? something like

local start = ngx.now()

ngx.say(start)

--calling the function

local end = ngx.now()

ngx.say(end)

It didn't work. Would you mind pointing me the right way? And how can I monitor speed in an nginx location block? Is it just simple ab?

Thanks in advance.

Best Regards,

arthurx

agentzh於 2013年10月28日星期一UTC+8上午3時58分33秒寫道：

Hello!

On Fri, Oct 25, 2013 at 11:50 PM, <fc2...@gmail.com> wrote:
> I am trying to write a custom lua-redis function that potential involved
> thousands of temporary variable (like getting the thousands of values from
> redis first and then do manipulation in lua).
> So one can use the redis eval function to run such a script, or by using
> openresty, one can write the lua script that use lua-resty-redis.
> In principle, which method should be preferred?
>

It depends. Generally, in-redis Lua script should stay simple enough
to prevent blocking the single-threaded Redis server for too long.

Why not just compare two approaches yourself? :)

Best regards,
-agentzh

agentzh

Hello!

On Sun, Oct 27, 2013 at 10:24 PM, arthurx wrote:
>
> I used ngx.say(os.clock()) at the end of my lua script. Supposedly it is the
> whole run time of the lua script?
> However how can I monitor the run time of a specific function inside a lua
> script?

I usually use the following code to test the speed of a Lua function,
say, foo():

    local begin = ngx.now()
    for i = 1, 20000 do
        foo()
    end
    ngx.update_time()
    local elapsed = ngx.now() - begin
    ngx.say("elapsed: ", elapsed)

The magic number 20000 is just an example, and you should adjust it
according to the actual overhead of foo() to prevent waiting for too
short or too long.

Note how we use ngx.update_time() to update the cached time in the Nginx core.

> And how can I
> monitor speed in an nginx location block? Is it just simple ab?

Well, ab works. Just always specify the -k option to save the TCP
connect() overhead.

Regards,
-agentzh

fc28222

Thanks a lot agentzh!