Pull Request Review Bottlenecks

What This Looks Like

A developer opens a pull request and waits. Hours pass. A day passes. They ping someone in chat. The reviewer is busy with their own work. Eventually, late in the afternoon or the next morning, comments arrive. The author has moved on to something else and has to reload context to respond. Another round of comments. Another wait. The PR finally merges two or three days after it was opened.

Common variations:

• The aging PR queue. The team has five or more open PRs at any given time. Some are days old. Developers start new work while they wait, which creates more PRs, which creates more review load, which slows reviews further.
• The designated reviewer. One or two senior developers review everything. They are overwhelmed. Their review queue is a bottleneck that the rest of the team works around by starting more work while they wait.
• The drive-by approval. Reviews are so slow that the team starts rubber-stamping PRs to unblock each other. The review step exists in name only. Quality drops, but at least things merge.
• The nitpick spiral. Reviewers leave dozens of style comments on formatting, naming, and conventions that could be caught by a linter. Each round triggers another round. A 50-line change accumulates 30 comments across three review cycles.
• The “I’ll get to it” pattern. When asked about a pending review, the answer is always “I’ll look at it after I finish this.” But they never finish “this” because they have their own work, and reviewing someone else’s code is never the priority.

The telltale sign: the team tracks PR age and the average is measured in days, not hours.

Why This Is a Problem

Slow code review is not just an inconvenience. It is a systemic bottleneck that undermines continuous integration, inflates cycle time, and degrades the quality it is supposed to protect.

It blocks continuous integration

Trunk-based development requires integrating to trunk at least once per day. A PR that sits for two days makes daily integration impossible. The branch diverges from trunk while it waits. Other developers make changes to the same files. By the time the review is done, the PR has merge conflicts that require additional work to resolve.

This is a compounding problem. Slow reviews cause longer-lived branches. Longer-lived branches cause larger merge conflicts. Larger merge conflicts make integration painful. Painful integration makes the team dread merging, which makes them delay opening PRs until the work is “complete,” which makes PRs larger, which makes reviews take longer.

In teams where reviews complete within hours, branches rarely live longer than a day. Merge conflicts are rare because changes are small and trunk has not moved far since the branch was created.

It inflates cycle time

Every hour a PR waits for review is an hour added to cycle time. For a story that takes four hours to code, a two-day review wait means the review step dominates the total cycle time. The coding was fast. The pipeline is fast. But the work sits idle for days because a human has not looked at it yet.

This wait time is pure waste. Nothing is happening to the code while it waits. No value is being delivered. The change is done but not integrated, tested in the full pipeline, or deployed. It is inventory sitting on the shelf.

When reviews happen within two hours, the review step nearly disappears from the cycle time measurement. Code flows from development to trunk to production with minimal idle time.

It degrades the review quality it is supposed to protect

Slow reviews produce worse reviews, not better ones. When a reviewer sits down to review a PR that was opened two days ago, they have no context on the author’s thinking. They review the code cold, missing the intent behind decisions. They leave comments that the author already considered and rejected, triggering unnecessary back-and-forth.

Large PRs make this worse. When a review has been delayed, the author often keeps working on the same branch, adding more changes to avoid opening a second PR while the first one waits. What started as a 50-line change becomes a 300-line change. Research consistently shows that reviewer effectiveness drops sharply after 200 lines. Large PRs get superficial reviews - the reviewer skims the diff, leaves a few surface-level comments, and approves because they do not have time to review it thoroughly.

Fast reviews are better reviews. A reviewer who looks at a 50-line change within an hour of it being opened has full context on what the team is working on, can ask the author questions in real time, and can give focused attention to a small, digestible change.

It creates hidden WIP

Every open PR is work in progress. The code is written but not integrated. The developer who authored it has moved on to something new, but their previous work is still “in progress” from the team’s perspective. A team of five with eight open PRs has eight items of hidden WIP that do not appear on the sprint board as “in progress” but consume the same attention.

This hidden WIP interacts badly with explicit WIP. A developer who has one story “in progress” on the board but three PRs waiting for review is actually juggling four streams of work. Each PR that gets comments requires a context switch back to code they wrote days ago. The cognitive overhead is real even if the board does not show it.

Impact on continuous delivery

Continuous delivery requires that every change move from commit to production quickly and predictably. Review bottlenecks create an unpredictable queue between “code complete” and “integrated.” The queue length varies based on reviewer availability, competing priorities, and team habits. Some PRs merge in hours, others take days. This variability makes delivery timelines unpredictable and prevents the steady flow of small changes that CD depends on.

The bottleneck also discourages the small, frequent changes that make CD safe. Developers learn that every PR costs a multi-day wait, so they batch changes into larger PRs to reduce the number of times they pay that cost. Larger PRs are riskier, harder to review, and more likely to cause problems - exactly the opposite of what CD requires.

How to Fix It

Step 1: Measure review turnaround time (Week 1)

You cannot fix what you do not measure. Start tracking two numbers:

• Time to first review: elapsed time from PR opened to first reviewer comment or approval.
• PR age at merge: elapsed time from PR opened to PR merged.

Most teams discover their average is far worse than they assumed. Developers think reviews happen in a few hours. The data shows days.

Step 2: Set a team review SLA (Week 1)

Agree as a team on a review turnaround target. A reasonable starting point:

• Reviews within 2 hours during working hours.
• PR age at merge under 24 hours.

Write this down as a working agreement. Post it on the board. This is not a suggestion - it is a team commitment.

Step 3: Make reviews a first-class activity (Week 2)

The core behavior change: reviewing code is not something you do when you have spare time. It is the highest-priority activity after your current task reaches a natural stopping point.

Concrete practices:

• Check for open PRs before starting new work. When a developer finishes a task or hits a natural pause, their first action is to check for pending reviews, not to pull a new story.
• Auto-assign reviewers. Do not wait for someone to volunteer. Configure your tools to assign a reviewer automatically when a PR is opened.
• Rotate reviewers. Do not let one or two people carry all the review load. Any team member should be able to review any PR. This spreads knowledge and distributes the work.
• Keep PRs small. Target under 200 lines of changed code. Small PRs get reviewed faster and more thoroughly. If a developer says their PR is “too large to split,” that is a work decomposition problem.

Step 4: Consider synchronous review (Week 3+)

The fastest review is one that happens in real time. If async review consistently exceeds the team’s SLA, move toward synchronous alternatives:

Pair programming eliminates the review bottleneck entirely. The code is reviewed as it is written. There is no PR, no queue, and no wait. For teams that struggle with review latency, pairing is often the most effective solution.

Step 5: Address the objections

Measuring Progress

Related Content

• Code Review - The practice guide for CD-compatible review techniques
• Trunk-Based Development - Daily integration requires fast reviews
• Push-Based Work Assignment - Push assignment makes reviews feel like a distraction from “my work”
• Too Much Work in Progress - Slow reviews create hidden WIP as PRs queue up
• Work Decomposition - Small PRs start with small stories