After every merge the train fetches the merge commit and compares its tree with the tree that was gated.
Merged pull requests per hour (UTC)
Per round; bisection included. Below 1 means batching paid off.
Per round: round duration divided by pull requests merged.
Each gate run: waiting (from the round start, or from when its parent batch went red), gating, then landing.
A red batch is split in halves and each half is gated again, until the failing pull request is held on its own.
Held pull requests are not read again until their head or what they depended on changes.