Using lua-resty-redis. Always need to call so_keepalive?

ssimpson · 2014-03-01T07:38:54+00:00

On Wed, Feb 26, 2014 at 9:58 AM, David Birdsong <david....@gmail.com> wrote: Having just gone through learning about this over the last few days, he...

Using lua-resty-redis. Always need to call so_keepalive?

ssimpson

I'm using lua-resty-redis with nginx to talk to a redis server. The manual page for lua-resty-redis shows a call so so_keepalive to return the connection to the pool at the end of the example program. It doesn't show a call to so_keepalive for an error return. Does this call need to be done for all returns? Is the connection returned to the connection pool automatically when the lua script runs out of scope? Thank you.

agentzh

Hello!

On Fri, Feb 28, 2014 at 3:38 PM,  ssimpson wrote:
> I'm using lua-resty-redis with nginx to talk to a redis server. The manual
> page for lua-resty-redis shows a call so so_keepalive to return the
> connection to the pool at the end of the example program. It doesn't show a
> call to so_keepalive for an error return.

You mean "set_keepalive" instead of "so_keepalive" here, right?

Yes, you should only put a good connection into the pool.

> Does this call need to be done for
> all returns?

Nope, just for code paths you can safely reuse the connections. Also
keep in mind that Redis connections can carry state, as in pub/sub
mode. Reusing stateful Redis connections requires special caution.

> Is the connection returned to the connection pool automatically
> when the lua script runs out of scope? Thank you.
>

The connection is automatically shut down when the cosocket object is
collected. The decision has been made that blindly putting unused
connections into the pool is a dangerous thing to do. In many cases,
only the user knows whether the current connection is safe to get
reused.

Best regards,
-agentzh

ssimpson

Sorry. I meant set_keepalive. My bad. So if you don't know why the request didn't work, don't reuse the connection by putting it back in the pool. Got it. I assume doing a close() here is equivalent to doing nothing since the cosocket object will be collected anyways.

agentzh

Hello!

On Mon, Mar 3, 2014 at 8:39 AM,  wrote:
> So if you don't know why the request
> didn't work, don't reuse the connection by putting it back in the pool. Got
> it.

For most socket errors (the only exception right now is the read
timeout error), the underlying cosocket will automatically close the
connection. So double-close such cosocket has no good.

> I assume doing a close() here is equivalent to doing nothing since the
> cosocket object will be collected anyways.
>

But calling close() explicitly when the cosocket is not closed (like
due to errors) is more efficient than letting the Lua GC do the work
with a delay.

Regards,
-agentzh