[ovs-discuss] "ovs-vsctl get openvswitch . other_config" results in "WARN connection dropped"

[Ilya Maximets]

This warning is caused by db_change_aware message that idl sends to
ovsdb-server, but never actually waits for confirmation.  And while
trying to send the confirmation, ovsdb-server discovers that connection
was already closed on the other side.

This issue was already debugged by Dumitru and we even have a patch:
  http://patchwork.ozlabs.org/project/openvswitch/patch/1594380801-32134-1-git-send-email-dceara@redhat.com/

The problem I have with this patch and 'db_change_aware' handling in
general is that it's hacked into idl state machine instead of graceful
integration.  That is the actual root cause why idl doesn't wait for
the reply from the server.

The patch above is a not so clean way to fix the original not so clean
implementation.  So, it probably doesn't make things worse, but makes me
uncomfortable anyway.  On the other hand, graceful integration to the
state machine sounds like a too much work for such a simple thing.
And I guess, that was the thought behind the original implementation
of 'db_change_aware'.

I'm in doubts.

We might explore different ways to fix that though, e.g. allow
ovsdb-server to not reply to 'db_change_aware' requests if client
will set a special flag, or something like that.  Or we could
simply reduce the logging level for this kind of message on a
server side (might be not a good thing to do).

Best regards, Ilya Maximets.

> Probably, some debugging of the situation could lead to figuring out
> what's going on and thereby avoiding the messages.  I don't have the
> necessary cycles to do that myself.
> 
> On Mon, Feb 01, 2021 at 10:33:58PM +0000, Tobias Hofmann (tohofman) wrote:
>> I just see the warning, however on our system we periodically run “ovs-vsctl get openvswitch . other_config” which bloats the log file over time. I’d like to prevent that.
>> 
>> From: Ben Pfaff <blp at ovn.org>
>> Date: Monday, 1. February 2021 at 22:09
>> To: Tobias Hofmann (tohofman) <tohofman at cisco.com>
>> Cc: ovs-discuss at openvswitch.org <ovs-discuss at openvswitch.org>
>> Subject: Re: [ovs-discuss] "ovs-vsctl get openvswitch . other_config" results in "WARN connection dropped"
>> On Mon, Feb 01, 2021 at 01:41:05PM +0000, Tobias Hofmann (tohofman) via discuss wrote:
>> > Hello everybody,
>> >
>> > I have Open vSwitch 2.11.1 installed with DPDK 18.11.0 and DB Schema 7.16.1.
>> > Every time I execute: “ovs-vsctl get open_vswitch . other_config”. I get the following WARN message in ovsdb-server.log:
>> > 2021-02-01T13:31:21.773Z|07709|jsonrpc|WARN|unix#7443: receive error: Connection reset by peer
>> > 2021-02-01T13:31:21.774Z|07710|reconnect|WARN|unix#7443: connection dropped (Connection reset by peer)
>> >
>> > When running: ”ovs-vsctl show” I don’t see any of these WARN logs.
>> > Interestingly, when running: “ovs-vsctl -vjsonrpc get open_vswitch . other_config”. I also DO NOT see any WARN log messages.
>> >
>> > Does anyone have an idea what causes this issue and how to fix it?
>> 
>> Do you see some actual issue, or just a warning message in the log?  The
>> most probable reason for the message is that ovsdb-server has some RPC
>> message queued up to send ovs-vsctl, but ovs-vsctl is done and exits
>> without reading it.  Probably, adding -vjsonrpc slows ovs-vsctl down
>> enough that it reads that RPC, suppressing the log.