[ovs-dev] scale test testing requests (was: raft ovsdb clustering with scale test)

Ben Pfaff blp at ovn.org
Fri May 18 20:35:45 UTC 2018


I've spent some time stressing the database yesterday and today.  So
far, I can't reproduce these particular problems.  I do see various ways
to improve OVS and OVN and their tests.

Here are some suggestions I have for further testing:

1. You mentioned that programs were segfaulting.  They should not be
   doing that (obviously) but I wasn't able to get them to do so in my
   own testing.  It would be very helpful to have backtraces.  Would you
   mind trying to get them?

2. You mentioned that "perf" shows that lots of time is being spent
   writing snapshots.  It would be helpful to know whether this is a
   contributing factor in the failures.  (If it is, then I will work on
   making snapshots faster.)  One way to figure that out would be to
   disable snapshots entirely for testing.  That isn't acceptable in
   production because it will use up all the disk space eventually, but
   for testing one could apply the following patch:

diff --git a/ovsdb/storage.c b/ovsdb/storage.c
index 446cae0861ec..9fa9954b6d35 100644
--- a/ovsdb/storage.c
+++ b/ovsdb/storage.c
@@ -490,38 +490,8 @@ schedule_next_snapshot(struct ovsdb_storage *storage, bool quick)
 }
 
 bool
-ovsdb_storage_should_snapshot(const struct ovsdb_storage *storage)
+ovsdb_storage_should_snapshot(const struct ovsdb_storage *storage OVS_UNUSED)
 {
-    if (storage->raft || storage->log) {
-        /* If we haven't reached the minimum snapshot time, don't snapshot. */
-        long long int now = time_msec();
-        if (now < storage->next_snapshot_min) {
-            return false;
-        }
-
-        /* If we can't snapshot right now, don't. */
-        if (storage->raft && !raft_may_snapshot(storage->raft)) {
-            return false;
-        }
-
-        uint64_t log_len = (storage->raft
-                            ? raft_get_log_length(storage->raft)
-                            : storage->n_read + storage->n_written);
-        if (now < storage->next_snapshot_max) {
-            /* Maximum snapshot time not yet reached.  Take a snapshot if there
-             * have been at least 100 log entries and the log file size has
-             * grown a lot. */
-            bool grew_lots = (storage->raft
-                              ? raft_grew_lots(storage->raft)
-                              : ovsdb_log_grew_lots(storage->log));
-            return log_len >= 100 && grew_lots;
-        } else {
-            /* We have reached the maximum snapshot time.  Take a snapshot if
-             * there have been any log entries at all. */
-            return log_len > 0;
-        }
-    }
-
     return false;
 }
 

3. This isn't really a testing note but I do see that the way that OVSDB
   is proxying writes from a Raft follower to the leader is needlessly
   inefficient and I should rework it for better write performance.


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