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Slow perceived response time due to excessive storage writes during streaming #11329
Description
Description
During streaming responses, OpenCode writes to storage (JSON files) on every reasoning-delta event. With fast streaming APIs, this results in hundreds of file writes per second.
Impact
- High I/O overhead from frequent file system operations
- Increased latency between receiving content and displaying it
- Slower perceived response time compared to native CLI tools (e.g., kiro-cli)
Root Cause
In processor.ts, every delta triggers a storage write:
case "reasoning-delta":
if (part.text) await Session.updatePart({ part, delta: value.text })Session.updatePart calls Storage.write which writes to the file system on every call.
Proposed Solution
Throttle storage writes during streaming:
- Accumulate content in memory
- Only flush to storage every 50ms
- Always flush on
reasoning-end
Environment
- OpenCode version: latest
- Tested with Kiro API streaming responses
Activity
github-actions commentedon Jan 30, 2026
This issue might be a duplicate of existing issues. Please check:
Feel free to ignore if none of these address your specific case.
taetaetae commentedon Jan 30, 2026
Thanks for flagging #6172! After reviewing it, I believe these are different issues addressing different bottlenecks:
textBufferViewMeasureForDimensions→mmapSession.updatePart→Storage.write→Bun.writeprocessor.ts#6172 addresses CPU usage from re-rendering the entire text buffer on every update.
This issue addresses I/O overhead from writing to disk on every streaming delta in
processor.ts:Both optimizations are complementary - fixing one doesn't fix the other. The PR #11328 addresses this specific storage I/O bottleneck.
buildkloe commentedon Feb 1, 2026
Confirming significant disk I/O impact
Experiencing 11.2 MB/s sustained writes from OpenCode (desktop and CLI) during normal usage or idle state - more than any other process on the system. This is visible in macOS Activity Monitor as continuous disk activity even no operation at all.
I'm a bit worry about the impact:
SSD wear from constant writes during every session
Competes with other disk I/O (spotlight indexing)
Battery drain on laptops
Would love to see FIX/PR #11328 prioritized.
Thank you!
github-actions commentedon Apr 3, 2026
To stay organized issues are automatically closed after 90 days of no activity. If the issue is still relevant please open a new one.