---
title: "Batch Bisection Statistics API"
date: 2026-03-12
tags:
  - Merge Queue
  - API
description: "New API endpoint to track merge queue bisection events, helping users optimize their batch size configuration."
---

Bisection is a key signal for batch size optimization:

- **Frequent bisections** suggest the batch size may be too large, causing more CI failures and slower throughput
- **No bisections** may indicate room to increase batch size for better merge velocity
- **Deep bisections** (high depth) reveal that failures are hard to isolate, possibly due to flaky tests or complex interactions
## What's Tracked

### Bisection Start Events

Emitted when a failed batch is split into sub-batches:

- **Batch size before split** — how large the batch was when it failed
- **Number of sub-batches** — how many pieces it was divided into
- **Bisection depth** — 0 for the first split, increments for nested splits
- **Whether it's top-level** — distinguishes root splits from recursive ones
### Bisection End Events

Emitted when the culprit PR is identified:

- **Culprit PR numbers** — which PR(s) caused the failure
- **Remaining PR numbers** — PRs that were re-queued after culprit removal
- **Max failure resolution reached** — whether the bisection hit the configured retry limit