Merge bitcoin/bitcoin#25970: Add headerssync tuning parameters optimization script to repo

3d420d8f28f2d351abf8b0afe90848110e15d50c Add instructions for headerssync-params.py to release-process.md (Pieter Wuille)
53d7d35b5899685cd1577156250068e0cab502f4 Update parameters in headerssync.cpp (Pieter Wuille)
7899402cff708319b1c5181242a97557eefe1ae7 Add headerssync-params.py script to the repository (Pieter Wuille)

Pull request description:

  Builds upon #25946, as it incorporates changes based on the selected values there.

  This adds the headerssync tuning parameters optimization script from https://gist.github.com/sipa/016ae445c132cdf65a2791534dfb7ae1 to the repository, updates the parameters based on its output, and adds release process instructions for doing this update in the future.

  A few considerations:
  * It would be a bit cleaner to have these parameters be part of `CChainParams`, but due to the nature of the approach, it really only applies to chains with unforgeable proof-of-work, which we really can only reasonably expect from mainnet, so I think it's fine to keep them local to `headerssync.cpp`. Keeping them as compile-time evaluatable constants also has a (likely negligible) performance impact (avoiding runtime modulo operations).
  * If we want to make sure the chainparams and headerssync params don't go out of date, it could be possible to run the script in CI, and and possibly even have the parameters be generated automatically at build time. I think that's overkill for how unfrequently these need to change, and running the script has non-trivial cost (~minutes in the normal python interpreter).
  * A viable alternative is just leaving this out-of-repo entirely, and just do ad-hoc updating from time to time. Having it in the repo and release notes does make sure it's not forgotten, though adds a cost to contributors/maintainers who follow the process.

ACKs for top commit:
  ajtowns:
    reACK 3d420d8f28f2d351abf8b0afe90848110e15d50c

Tree-SHA512: 03188301c20423c72c1cbd008ccce89b93e2898edcbeecc561b2928a0d64e9a829ab0744dc3b017c23de8b02f3c107ae31e694302d3931f4dc3540e184de1963

1 files changed, 5 insertions, 5 deletions

diff --git a/src/headerssync.cpp b/src/headerssync.cpp
index f891063cd2..1b5d7305e8 100644
--- a/src/headerssync.cpp
+++ b/src/headerssync.cpp
@@ -9,15 +9,15 @@
 #include <util/check.h>
 #include <util/vector.h>
 
-// The two constants below are computed using the simulation script on
-// https://gist.github.com/sipa/016ae445c132cdf65a2791534dfb7ae1
+// The two constants below are computed using the simulation script in
+// contrib/devtools/headerssync-params.py.
 
-//! Store a commitment to a header every HEADER_COMMITMENT_PERIOD blocks.
-constexpr size_t HEADER_COMMITMENT_PERIOD{584};
+//! Store one header commitment per HEADER_COMMITMENT_PERIOD blocks.
+constexpr size_t HEADER_COMMITMENT_PERIOD{600};
 
 //! Only feed headers to validation once this many headers on top have been
 //! received and validated against commitments.
-constexpr size_t REDOWNLOAD_BUFFER_SIZE{13959}; // 13959/584 = ~23.9 commitments
+constexpr size_t REDOWNLOAD_BUFFER_SIZE{14308}; // 14308/600 = ~23.8 commitments
 
 // Our memory analysis assumes 48 bytes for a CompressedHeader (so we should
 // re-calculate parameters if we compress further)