ovsdb raft: Fix election timer parsing in snapshot RPC.

Commit a76ba82 took care of saving and restoring election timer in
file header snapshot, but it didn't handle the parsing of election
timer in install_snapshot_request/reply RPC, which results in problems,
e.g. when election timer change log is compacted in snapshot and then a
new node join the cluster, the new node will use the default timer
instead of the new value.  This patch fixed it by parsing election
timer in snapshot RPC.

At the same time the patch updates the test case to cover the DB compact and
join senario. The test reveals another 2 problems related to clustered DB
compact, as commented in the test case's XXX, which need to be addressed
separately.

Signed-off-by: Han Zhou <hzhou@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

ovsdb/raft-rpc.c

@@ -511,6 +511,7 @@ raft_install_snapshot_request_to_jsonrpc(
     json_object_put(args, "last_servers", json_clone(rq->last_servers));
     json_object_put_format(args, "last_eid",
                            UUID_FMT, UUID_ARGS(&rq->last_eid));
+    raft_put_uint64(args, "election_timer", rq->election_timer);
 
     json_object_put(args, "data", json_clone(rq->data));
 }
@@ -527,6 +528,9 @@ raft_install_snapshot_request_from_jsonrpc(
     rq->last_index = raft_parse_required_uint64(p, "last_index");
     rq->last_term = raft_parse_required_uint64(p, "last_term");
     rq->last_eid = raft_parse_required_uuid(p, "last_eid");
+    /* election_timer is optional in file header, but is always populated in
+     * install_snapshot_request. */
+    rq->election_timer = raft_parse_required_uint64(p, "election_timer");
 
     rq->data = json_nullable_clone(
         ovsdb_parser_member(p, "data", OP_OBJECT | OP_ARRAY));
@@ -541,6 +545,7 @@ raft_format_install_snapshot_request(
     ds_put_format(s, " last_term=%"PRIu64, rq->last_term);
     ds_put_format(s, " last_eid="UUID_FMT, UUID_ARGS(&rq->last_eid));
     ds_put_cstr(s, " last_servers=");
+    ds_put_format(s, " election_timer=%"PRIu64, rq->election_timer);
 
     struct hmap servers;
     struct ovsdb_error *error =

ovsdb/raft.c

@@ -3257,7 +3257,7 @@ raft_send_install_snapshot_request(struct raft *raft,
             .last_servers = raft->snap.servers,
             .last_eid = raft->snap.eid,
             .data = raft->snap.data,
-            .election_timer = raft->election_timer,
+            .election_timer = raft->election_timer, /* use latest value */
         }
     };
     raft_send(raft, &rpc);

tests/ovsdb-cluster.at

@@ -233,6 +233,55 @@ done
 OVS_WAIT_UNTIL([ovs-appctl -t "`pwd`"/s1 cluster/status $schema_name | grep "Election timer: 4000"])
 OVS_WAIT_UNTIL([ovs-appctl -t "`pwd`"/s2 cluster/status $schema_name | grep "Election timer: 4000"])
 
+# Latest timer should be restored after DB compact and restart.
+# This is to test the install_snapshot RPC.
+
+# XXX: Insert data before compact, because otherwise transaction will trigger
+# busy loop after compact.
+# poll_loop|DBG|wakeup due to 0-ms timeout at ../ovsdb/trigger.c:164 (89% CPU usage)
+AT_CHECK([ovsdb-client transact unix:s1.ovsdb '[["idltest",
+      {"op": "insert",
+       "table": "simple",
+       "row": {"i": 1}}]]'], [0], [ignore], [ignore])
+
+# Compact online
+for i in `seq $n`; do
+    AT_CHECK([ovs-appctl -t "`pwd`"/s$i ovsdb-server/compact])
+done
+
+# XXX: Insert data after compact, because otherwise vote will fail after
+# cluster restart after compact. There will be error logs like:
+# raft|ERR|internal error: deferred vote_request message completed but not ready to send because message index 9 is past last synced index 0: s2 vote_request: term=6 last_log_index=9 last_log_term=4
+AT_CHECK([ovsdb-client transact unix:s1.ovsdb '[["idltest",
+      {"op": "insert",
+       "table": "simple",
+       "row": {"i": 1}}]]'], [0], [ignore], [ignore])
+
+for i in `seq $n`; do
+    printf "\ns$i: stopping\n"
+    OVS_APP_EXIT_AND_WAIT_BY_TARGET([`pwd`/s$i], [s$i.pid])
+done
+for i in `seq $n`; do
+    AT_CHECK([ovsdb-server -v -vconsole:off -vsyslog:off --detach --no-chdir --log-file=s$i.log --pidfile=s$i.pid --unixctl=s$i --remote=punix:s$i.ovsdb s$i.db])
+done
+for i in `seq $n`; do
+    OVS_WAIT_UNTIL([ovs-appctl -t "`pwd`"/s$i cluster/status $schema_name | grep "Election timer: 4000"])
+done
+
+# Wait until cluster is ready
+for i in `seq $n`; do
+    OVS_WAIT_WHILE([ovs-appctl -t "`pwd`"/s$i cluster/status $schema_name | grep "Leader: unknown"])
+done
+
+# Newly joined member should use latest timer value
+AT_CHECK([ovsdb-tool join-cluster s4.db $schema_name unix:s4.raft unix:s1.raft])
+AT_CHECK([ovsdb-server -v -vconsole:off -vsyslog:off --detach --no-chdir --log-file=s4.log --pidfile=s4.pid --unixctl=s4 --remote=punix:s4.ovsdb s4.db])
+OVS_WAIT_UNTIL([ovs-appctl -t "`pwd`"/s4 cluster/status $schema_name | grep "Election timer: 4000"])
+# for i in `seq 10`; do
+#     ovs-appctl -t "`pwd`"/s4 cluster/status $schema_name
+#     sleep 1
+# done
+
 AT_CLEANUP