SRCache with Lua - would subrequest ever read from file or always from memory ?

ddragosd · 2016-03-29T14:22:29+00:00

Thanks, that's what I've done and it works. For anyone else reading this in the future, this is essentially what I've done:http { include m...

SRCache with Lua - would subrequest ever read from file or always from memory ?

ddragosd

Hi,

I'm working on a simple cache-manager module - [1] to make it easier to manage a multi-layered cache data store using a simple interface:

my_cache:get(key)

my_cache:put(key,value)

my_cache can be configured with multiple data stores such as Redis and shared_dict; a put method would save the key,value pair in both stores, and a get operation would lookup the key first in the shared_dict and then if it's not there it would lookup the key in Redis, then it would save the returned value from Redis into the shared_dict for the next time get is invoked.

This module works OOTB with the srcache module but in my tests I'm not able to test the scenario when the file is buffered to disk and the lua code needs to invoke ngx.req.get_body_file()

I've been trying to define the subrequest with client_body_in_file_only on; but in the logs I keep seeing:

[debug] 17#0: *1 lua start to read buffered request body

[debug] 17#0: *1 lua req body post read, c:3

[debug] 17#0: *1 lua has read buffered request body in a single run

Even though NGINX is buffering the response to disk:

[warn] 17#0: *1 an upstream response is buffered to a temporary file /usr/local/api-gateway/proxy_temp/1/00/0000000001 while reading upstream, client: 192.168.75.1, server: , request: "GET /cache/img_test.JPG HTTP/1.1", upstream: "http://127.0.0.1:80/html/img_test.JPG", host: "192.168.75.158"

Content-Length: 2858221

Should we conclude that subrequests and/or srcache would always read the content from the memory regardless of what NGINX does ? If not, how should I write a test for this use case ? Is there a setting I could use to force lua to read from the file ?

Thanks,

dragos dascalita haut

[1] - https://github.com/adobe-apiplatform/api-gateway-cachemanager

ddragosd

Update: I've tried with a ~30MB payload and the logs show the same thing:

[debug] 17#0: *1 lua start to read buffered request body

[debug] 17#0: *1 lua req body post read, c:3

[debug] 17#0: *1 lua has read buffered request body in a single run

I've also set max_ranges 0; to disable 206 Partial Content which srcache skips by default.

At this point, based on my test results I'm tempted to conclude that for srcache the content is never read from a file, but it's always read using ngx.req.get_body_data()

Feel free to keep me honest.

Thanks,

dragos

On Monday, March 28, 2016 at 11:22:30 PM UTC-7, Dragos Dascalita Haut wrote:

Hi,
I'm working on a simple cache-manager module - [1] to make it easier to manage a multi-layered cache data store using a simple interface:

my_cache:get(key)
my_cache:put(key,value)

my_cache can be configured with multiple data stores such as Redis and shared_dict; a put method would save the key,value pair in both stores, and a get operation would lookup the key first in the shared_dict and then if it's not there it would lookup the key in Redis, then it would save the returned value from Redis into the shared_dict for the next time get is invoked.

This module works OOTB with the srcache module but in my tests I'm not able to test the scenario when the file is buffered to disk and the lua code needs to invoke ngx.req.get_body_file()
I've been trying to define the subrequest with client_body_in_file_only on; but in the logs I keep seeing:

[debug] 17#0: *1 lua start to read buffered request body

[debug] 17#0: *1 lua req body post read, c:3

[debug] 17#0: *1 lua has read buffered request body in a single run

Even though NGINX is buffering the response to disk:

[warn] 17#0: *1 an upstream response is buffered to a temporary file /usr/local/api-gateway/proxy_temp/1/00/0000000001 while reading upstream, client: 192.168.75.1, server: , request: "GET /cache/img_test.JPG HTTP/1.1", upstream: "http://127.0.0.1:80/html/img_test.JPG", host: "192.168.75.158"

Content-Length: 2858221

Should we conclude that subrequests and/or srcache would always read the content from the memory regardless of what NGINX does ? If not, how should I write a test for this use case ? Is there a setting I could use to force lua to read from the file ?

Thanks,
dragos dascalita haut

[1] - https://github.com/adobe-apiplatform/api-gateway-cachemanager

agentzh

Hello!

On Mon, Mar 28, 2016 at 11:22 PM, Dragos Dascalita Haut wrote:
> Should we conclude that subrequests and/or srcache would always read the
> content from the memory regardless of what NGINX does ? If not, how should I
> write a test for this use case ? Is there a setting I could use to force lua
> to read from the file ?
>

ngx_srcache's srcache_fetch triggers client request body reading using
NGINX core's own facility. So disk buffering should work as usual
AFAIK. If things do not work for you, then maybe you should prepare a
minimal and standalone example that I can run and analyze easily on my
side :)

Thanks and sorry for the delay on my side!

Best regards,
-agentzh