ovsdb-server: Allow replication from older schema version servers.

Presently, replication is not allowed if there is a schema version mismatch between
the schema returned by the active ovsdb-server and the local db schema. This is
causing failures in OVN DB HA deployments during uprades.

In the case of OpenStack tripleo deployment with OVN, OVN DB ovsdb-servers are
deployed on a multi node controller cluster in active/standby mode. During
minor updates or major upgrades, the cluster is updated one at a time. If
a node A is running active OVN DB ovsdb-servers and when it is updated, another
node B becomes active. After the update when OVN DB ovsdb-servers in A are started,
these ovsdb-servers fail to replicate from the active if there is a schema
version mismatch.

This patch addresses this issue by allowing replication even if there is a
schema version mismatch only if all the active db schema tables and its colums are
present in the local db schema.

This should not result in any data loss.

Signed-off-by: Numan Siddique <numans@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/ovsdb-replication.at b/tests/ovsdb-replication.at
index f81381bdb..82c416052 100644
--- a/tests/ovsdb-replication.at
+++ b/tests/ovsdb-replication.at
@@ -19,6 +19,29 @@ replication_schema () {
     }
 EOF
 }
+replication_schema_v2 () {
+    cat <<'EOF'
+    {"name": "mydb",
+     "tables": {
+       "a": {
+         "columns": {
+           "number": {"type": "integer"},
+           "name": {"type": "string"}},
+         "indexes": [["number"]]},
+       "b": {
+         "columns": {
+           "number": {"type": "integer"},
+           "name": {"type": "string"},
+           "foo" : {"type": "string"}},
+         "indexes": [["number"]]},
+       "c": {
+         "columns": {
+           "number": {"type": "integer"},
+           "name": {"type": "string"}},
+         "indexes": [["number"]]}}
+    }
+EOF
+}
 ]
 m4_divert_pop([PREPARE_TESTS])