lots of [io.netty.channel.nio.NioEventLoop select] warnings

[Siqin WANG]

Hello,

In our production environment, we have a lots of netty warning as below :

Jul 23, 2015 3:17:25 PM io.netty.channel.nio.NioEventLoop select

WARNING: Selector.select() returned prematurely 512 times in a row; rebuilding selector.

Jul 23, 2015 3:17:25 PM io.netty.channel.nio.NioEventLoop rebuildSelector

INFO: Migrated 1 channel(s) to the new Selector.

...

I've searched for some explanation on the internet. It is said to be a netty solution of a jdk bug (https://github.com/netty/netty/issues/2426).

Is it normal to have such kind of warnings while running a vertx application ? 

Thank you.

Siqin

[Nat]

What version of Netty do you use in your production environment?

[Siqin WANG]

Hi Nat,

We don't use Netty directly in our application. So it is the 4.0.21.Final version (netty-all-4.0.21.Final.jar) which is used by Vertx (v 2.1.5).

And I wonder if these warnings can be related to the cause of the exceptions mentioned in my early posts.

Thanks.

Siqin 

[Nat]

What linux kernel are you using? I have seen people mentioning that Linux 3.10 is the cause of this issue.

[Siqin WANG]

It's 3.19.0-25-generic.

Is it normal to have theses warnings ?

[Nat]

How often does it occur? If it does not happen very very often, it should be okay.

[Siqin WANG]

That depends on whether the load is important. When that happens, the warnings occur every 5-10 minutes.

[Nat]

This particular bug was causing a high CPU issue due to excessive selector list rebuild. If it only occurs once every 5-10 minutes, it should be okay.