fuzz: Fix timeout in `txorphan` #35289

pull marcofleon wants to merge 1 commits into bitcoin:master from marcofleon:2026/05/fix-txorphan-timeout changing 1 files +4 −0

marcofleon commented at 1:42 PM on May 14, 2026: contributor

The EraseForBlock branch in the txorphan harness could produce a block with 1000 transactions in it, each with potentially up to 200,000 inputs, resulting in way too many map lookups. This was producing inputs that were taking 2 seconds or longer per iteration, which is too long.

Fix by only adding transactions to the block up to the block weight limit. This matches production behavior, as EraseForBlock is only called on a newly connected block.
fuzz: Fix txorphan timeout by limiting block weight 004a7e3cfb
DrahtBot added the label Fuzzing on May 14, 2026
DrahtBot commented at 1:42 PM on May 14, 2026: contributor



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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35289.



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ACK maflcko, sedited, instagibbs

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marcofleon commented at 1:47 PM on May 14, 2026: contributor
Can be tested by running the harness on this input: txorphan-timeout.txt
```
FUZZ=txorphan ./fuzzbuild/bin/fuzz txorphan-timeout.txt
```
On master, it should take more than 2 seconds and with this PR significantly less.

Here's the flamegraph:

<img width="1200" height="406" alt="solution-6d51c5dbc793ebfce64809c2546ba34baf05bdd4" src="https://github.com/user-attachments/assets/5ab65615-6096-4581-b785-faba59d89f07" />
maflcko commented at 2:33 PM on May 14, 2026: member

lgtm ACK 004a7e3cfbc5b2118536651d2201cf8b72c87736
fanquake added the label Needs Backport (31.x) on May 14, 2026
sedited approved
sedited commented at 3:11 PM on May 14, 2026: contributor

ACK 004a7e3cfbc5b2118536651d2201cf8b72c87736
instagibbs commented at 3:14 PM on May 14, 2026: member

ACK 004a7e3cfbc5b2118536651d2201cf8b72c87736

Don't love "EraseForBlock" but this seems more realistic at least
sedited merged this on May 14, 2026
sedited closed this on May 14, 2026
fanquake referenced this in commit 7a97580997 on May 14, 2026
fanquake removed the label Needs Backport (31.x) on May 14, 2026
fanquake commented at 3:50 PM on May 14, 2026: member

Backported to 31.x in #35231.
nervana21 commented at 3:48 PM on May 15, 2026: contributor
post-merge tACK 004a7e3cfbc5b2118536651d2201cf8b72c87736

I used txorphan-timeout.txt and ran: FUZZ=txorphan build_fuzz/bin/fuzz -runs=1 fuzz_input/

Prior to this patch:
```
Done 2 runs in 10 second(s)

real    0m11.047s
user    0m10.505s
sys     0m0.165s
```
After applying this patch:
```
Done 2 runs in 0 second(s)

real    0m0.907s
user    0m0.260s
sys     0m0.193s
```