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[Bug]Deep clone of entire message history causes 30+ second delay with 200 messages #10187
Description
Description
Deep clone of entire message history causes 30+ second delay with 200 messages
Description
In long sessions (~200 messages), sending a new message takes 30+ seconds before getting any response. The delay is caused by a deep clone of the entire message history on every loop iteration.
Location
packages/opencode/src/session/prompt.ts, line 573:
const sessionMessages = clone(msgs)Why this is slow
The clone() function from remeda recursively copies:
- Every message object
- Every part (text, tool calls, attachments)
- All nested content including large tool outputs
With 200 messages × 5 parts each = 1000+ objects deep cloned per iteration.
Plugins
No response
OpenCode version
Latest
Steps to reproduce
- Build up a session with 100+ messages (long refactoring task)
- Send a new message
- Wait 30+ seconds before the model starts responding
- Observe the delay increases with message count
Screenshot and/or share link
No response
Operating System
macOS 26.2
Terminal
wave
Activity
[-]Deep clone of entire message history causes 30+ second delay with 200 messages[/-][+][Bug]Deep clone of entire message history causes 30+ second delay with 200 messages[/+]github-actions commentedon Jan 23, 2026
This issue might be a duplicate of existing issues. Please check:
Feel free to ignore if none of these address your specific case.
perf(opencode): replace deep clone with lazy shallow copy in prompt loop
Jaakkonen commentedon Feb 19, 2026
Reproduced this issue on latest main commit and took a flamegraph with
bun run --cpu-prof src/index.ts servewhile continuing a long session.This causes 100% CPU usage and really slow conversation. The PR #10190 seems to be fixing this issue properly.
After fixing that cloning issue the flamegraph looks something like
This can be fixed with a 1-line patch like
const sessionMessages = clone(msgs)->const sessionMessages = step > 1 && lastFinished ? structuredClone(msgs) : msgsutilizing Bun fast structuredClone.github-actions commentedon Apr 21, 2026
To stay organized issues are automatically closed after 60 days of no activity. If the issue is still relevant please open a new one.