[ovs-dev] [PATCH v3] ovsdb-cs: Perform forced reconnects without a backoff.

[Ilya Maximets]

On 7/21/21 2:51 PM, Dumitru Ceara wrote:
> The ovsdb-cs layer triggers a forced reconnect in various cases:
> - when an inconsistency is detected in the data received from the
>   remote server.
> - when the remote server is running in clustered mode and transitioned
>   to "follower", if the client is configured in "leader-only" mode.
> - when explicitly requested by upper layers (e.g., by the user
>   application, through the IDL layer).
> 
> In such cases it's desirable that reconnection should happen as fast as
> possible, without the current exponential backoff maintained by the
> underlying reconnect object.  Furthermore, since 3c2d6274bcee ("raft:
> Transfer leadership before creating snapshots."), leadership changes
> inside the clustered database happen more often and, therefore,
> "leader-only" clients need to reconnect more often too.
> 
> Forced reconnects call jsonrpc_session_force_reconnect() which will not
> reset backoff.  To make sure clients reconnect as fast as possible in
> the afore mentioned scenarios we first call the new API,
> jsonrpc_session_reset_backoff(), in ovsdb-cs, for sessions that are in
> state CS_S_MONITORING (i.e., the remote is likely still alive and
> functioning fine).
> 
> jsonrpc_session_reset_backoff() resets the number of backoff-free
> reconnect retries to the number of remotes configured for the session,
> ensuring that all remotes are retried exactly once with backoff 0.
> 
> This commit also updates the Python IDL and jsonrpc implementations.
> The Python IDL wasn't tracking the IDL_S_MONITORING state explicitly,
> we now do that too.  Tests were also added to make sure the IDL forced
> reconnects happen without backoff.
> 
> Reported-at: https://bugzilla.redhat.com/1977264
> Suggested-by: Ilya Maximets <i.maximets at ovn.org>
> Signed-off-by: Dumitru Ceara <dceara at redhat.com>
> ---
> v3:
> - Addressed Ilya's comments:
>   - rephrase commit log.
>   - fix jsonrpc_session_reset_backoff() comment.
>   - add extra backoff-free try only to connected jsonrpc sessions.
>   - fix comment for OVSDB_CHECK_CLUSTER_IDL_PY().
> 
> v2:
> https://patchwork.ozlabs.org/project/openvswitch/patch/20210721105614.25498-1-dceara@redhat.com/
> - Reworked the patch based on the discussion with Ilya:
>   - add a new jsonrpc_session_reset_backoff() API to be used by the
>     ovsdb-cs layer to avoid backoffs when reconnecting due to
>     inconsistent data/remote becoming follower.
> v1:
> https://patchwork.ozlabs.org/project/openvswitch/patch/20210629112035.17402-1-dceara@redhat.com/
> ---


Thanks!  Applied to master.  I also backported this down to 2.15
as it's the likely version stable versions of OVN are built with.

Best regards, Ilya Maximets.