mcp: avoid double-copy of payload in writeEvent#1106
Open
george1410 wants to merge 1 commit into
Open
Conversation
george1410
marked this pull request as ready for review
July 22, 2026 11:26
writeEvent built the SSE frame with fmt.Fprintf(&b, "data: %s\n\n", string(evt.Data)), which copies the payload into a fresh string and then again into the buffer, growing it via repeated bytes.growSlice doublings. For large MCP responses (e.g. ~162KB tools/list) under a burst of concurrent writes this ~3x amplifies allocations and peak heap. Write the payload directly into a pre-grown buffer instead. Output framing is byte-identical. Benchmarks (162KB payload): 517KB->172KB per op, 9->4 allocs/op, ~3x faster. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
george1410
force-pushed
the
incident-io/writeevent-no-double-copy
branch
from
July 22, 2026 11:28
1f1803a to
0061a33
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
writeEventbuilt the SSE frame withfmt.Fprintf(&b, "data: %s\n\n", string(evt.Data)), which copies the payload into a fresh string and then again into the buffer, growing it via repeatedbytes.growSlicedoublings. For large MCP responses (e.g. ~162KBtools/list) under a burst of concurrent writes this ~3x amplifies allocations and peak heap.Write the payload directly into a pre-grown buffer instead. Output framing is byte-identical. Benchmarks (162KB payload): 517KB->172KB per op, 9->4 allocs/op, ~3x faster.