Milo: Pubsub - Trim out pending build states if there are more than 25 per builder

milo/appengine/buildbot/pubsub.go

Index: milo/appengine/buildbot/pubsub.go
diff --git a/milo/appengine/buildbot/pubsub.go b/milo/appengine/buildbot/pubsub.go
index 81dd9bfbc5c2b51510ef89f411fedaf17b2a2868..cc3d42a9938e982df8d61d16fb9a9b915e057c03 100644
--- a/milo/appengine/buildbot/pubsub.go
+++ b/milo/appengine/buildbot/pubsub.go
@@ -75,6 +75,15 @@ type buildbotMasterEntry struct {
 
 func putDSMasterJSON(
 	c context.Context, master *buildbotMaster, internal bool) error {
+	// Trim pending build states.  These things are large and we can't really

[estaab, 2016/10/19 22:09:35]

How can we inform consumers that this was trimmed? We really need to do that.

[hinoka, 2016/10/19 22:23:11]

We send both the total number of pending builds (int) and details about the
first 25, so it would show up as something like

Pending Builds (100):
* detail...
* detail...
...23 more...

+	// store more than 25 of them.  If this becomes an issue again, we'll have
+	// to trim out things from the pending build state such as the changed
+	// file list, commit comments, etc.
+	for _, builder := range master.Builders {
+		if len(builder.PendingBuildStates) > 25 {
+			builder.PendingBuildStates = builder.PendingBuildStates[0:25]
+		}
+	}
 	entry := buildbotMasterEntry{
 		Name:     master.Name,
 		Internal: internal,