Batching

Testing each PR individually means one CI run per PR. With 10 PRs, that’s 10 CI runs. Batching groups multiple PRs into a single CI run, dramatically cutting CI cost and resource usage.

	Without Batching	With Batching
PRs	4	4
CI runs	4	1
Cost	4x	1x

How It Works

1. Multiple PRs enter the queue
2. The merge queue combines them into a single test branch
3. CI runs once against the combined changes
4. If it passes, all PRs merge together

Handling Failures

If the batch fails, the merge queue needs to identify which PR caused the failure. Common strategies:

Speculative Bisection

Test overlapping subsets in parallel. This allows partial merges while identifying failures.

Batch [1,2,3,4] fails
  → Test [1,2] and [1,2,3] in parallel
  → [1,2] passes → merge PR #1 and #2
  → [1,2,3] fails → PR #3 is the problem
  → Remove PR #3
  → Put PR #4 back in queue

Configuration Options

Setting	Description
Batch size	Maximum PRs per batch (e.g., 5, 10, unlimited)
Batch wait time	Time to wait for more PRs before starting CI

Trade-offs

Pros:

• Dramatically reduces CI cost and resource usage
• Fewer CI runs means less infrastructure load
• Works well with speculative checks for both speed and efficiency

Cons:

• One failure affects the whole batch
• Bisection adds latency when failures occur
• May need larger CI runners for combined changes