We check for up to n=50 pushheads in the artifact code, to account for the case we have pushes on central/inbound that haven't completed the relevant builds yet. This number is pretty high, and made it pretty weird to see 1332498 crop up long after we turned off some buildbot builds. This represents the number of pushes we might see at one time that don't have builds completed, or within about an hour. I expect this number would be highest for someone pulling from inbound, we should check push trends there to see if we can lower it.