[ovs-git] [openvswitch/ovs] 8190df: ovsdb-server: Don't drop all connections on read/w...

[numansiddique]

  Branch: refs/heads/branch-2.12
  Home:   https://github.com/openvswitch/ovs
  Commit: 8190df660ca6e8f58a579323bd5503c9357c9f21
      https://github.com/openvswitch/ovs/commit/8190df660ca6e8f58a579323bd5503c9357c9f21
  Author: Numan Siddique <nusiddiq at redhat.com>
  Date:   2019-10-14 (Mon, 14 Oct 2019)

  Changed paths:
    M ovsdb/jsonrpc-server.c

  Log Message:
  -----------
  ovsdb-server: Don't drop all connections on read/write status change.

The commit [1] force drops all connections when the db read/write status changes.
Prior to the commit [1], when there was read/write status change, the existing
jsonrpc sessions with 'db_change_aware' set to true, were not updated with the
changed 'read_only' value. If the db status was changed to 'standby', the existing
clients could still write to the db.

In the case of pacemaker OVN HA, OVN OCF script 'start' action starts the
ovsdb-servers in read-only state and later, it sets to read-write in the
'promote' action. We have observed that if some ovn-controllers connect to
the SB ovsdb-server (in read-only state) just before the 'promote' action,
the connection is not reset all the times and these ovn-controllers remain connected
to the SB ovsdb-server in read-only state all the time. Even though
the commit [1] calls 'ovsdb_jsonrpc_server_reconnect()' with 'forced' flag
set to true when the db read/write status changes, somehow the FSM misses resetting
the connections of these ovn-controllers.

I think this needs to be addressed in the FSM. This patch doesn't address
this FSM issue. Instead it changes the behavior of 'ovsdb_jsonrpc_server_set_read_only()'
by setting the 'read_only' flag of all the jsonrpc sessions instead of forcefully
resetting the connection.

I think there is no need to reset the connection. In large scale production
deployements with OVN, this results in unnecessary waste of CPU cycles as ovn-controllers
will have to connect twice - once during 'start' action and again during 'promote'.

[1] - 2a9679e3b2c6("ovsdb-server: drop all connections on read/write status change")

Acked-by: Dumitru Ceara <dceara at redhat.com>
Signed-off-by: Numan Siddique <nusiddiq at redhat.com>
Signed-off-by: Ben Pfaff <blp at ovn.org>