ngx.shared.DICT.set and exptime

amnon.david · 2013-12-15T20:43:47+00:00

For the life of me I cannot get this use case to work. I'm storing relevant headers in varchar fields and a (pre) gzipped content into a bytea field in a Pos...

ngx.shared.DICT.set and exptime

amnon.david

Hi,

I'm currently using the exptime parameter of ngx.shared.DICT.set to extend the validity of an entry in the openresty shared dictionary whenever some event occurs. However, I've noticed that it appears that the value of the entry expires after the period of the first ngx.shared.DICT.set operation, which means subsequent invocations of ngx.shared.DICT.set on the same key do not extend the lifetime of this key in the dictionary as I had expected.

I wanted to make sure I correctly understand the semantics of ngx.shared.DICT.set before diving deeper to see whether this can be an issue in my code - does setting the same key with the same value and same expiration time delay the expiration time of the key by the time specified ?

Thanks,

Amnon

agentzh

Hello!

On Sun, Dec 15, 2013 at 4:43 AM,  amnon.david wrote:
> However, I've noticed that it appears that the value of the
> entry expires after the period of the first ngx.shared.DICT.set operation,
> which means subsequent invocations of ngx.shared.DICT.set on the same key do
> not extend the lifetime of this key in the dictionary as I had expected.
>

set() overrides everything, including the expiration time. Consider
the following minimal example tested on my side:

    location = /t {
        content_by_lua '
            local dogs = ngx.shared.dogs
            dogs:set("foo", 32, 1)
            ngx.sleep(0.5)
            dogs:set("foo", 32, 1)
            ngx.sleep(0.6)
            local val = dogs:get("foo")
            ngx.say(val, " ", type(val))
        ';
    }

Then accessing /t gives

    32 number

which is expected. The second set() call overrides (and thus extend)
the exptime. If we comment out the second set() call, accessing /t
yields

    nil nil

The value is expired, also as expected.

Regards,
-agentzh