From: Frenchanfry <andujon18@gmail.com>
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Subject: [bitcoindev] By: Doctorbuzz1 {GitHub} Limit "Bulk Dust" with a default filter or consensus.
Date: Wed, 29 Oct 2025 17:03:45 -0700 (PDT) [thread overview]
Message-ID: <b0dee827-c2fe-4a68-9b41-f1447ba3c1d3n@googlegroups.com> (raw)
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A proposal on GitHub I found Highly interesting and a better improvement,
dealing with spammers/congestion.
I’m exploring a potential default filter or consensus-level rule (since a
large number of people believe that default filters don't work) to
discourage UTXO-bloat patterns without touching Script, witness data, or
the block size limit.
The idea is to target “bulk dust” transactions — those that create large
numbers of extremely small outputs — which are the main cause of long-term
UTXO set growth.
These types of "bulk dust" transactions have been the No. 1 reason cited
for wanting to expand the default OP_RETURN limit... and removing that
limit obviously influenced BIP 444. So it appears to me that there is
overwhelming majority support for limiting these types of "bulk dust"
transactions, as they do present a legitimate concern for node runners.
Concept
Flag a transaction as “bulk dust” if:
- It has >=100 outputs each below a dynamically defined TinyTx
threshold, and
- Those tiny outputs make up >=60% of all outputs in the transaction.
When flagged, it would be considered nonstandard (relay policy) or invalid
(if soft-forked into consensus).
TinyTx threshold (dynamic halving schedule)
I originally considered a constant definition of what was a "tiny" Tx to be
1,000 sats... but some might still just use 1,001 sats, right? Plus there
very likely will be a time where there is a valid use-case of >100 outputs
under 1,000 sats.
Rather than fixing the “tiny” threshold to a constant like 1,000 sats, the
rule defines it as a decreasing function of block height, starting high and
gradually tightening over time.
- Starts at 4096 sats when activated (target ~2028).
- Halves every 210,000 blocks (~4 years).
- Never falls below 1 sat (hard floor).
Year ---- Block Height -- TinyTx Threshold
2028 --- ~activation ---- 4096 sats
2032 --- ~1,260,000 ---- 2048 sats
2036 --- ~1,470,000 ---- 1024 sats
2040 --- ~1,680,000 ---- 512 sats
… -- every 210,000 blocks -- … until 1 sat floor
This gradual halving ensures the definition of "tiny" stays relevant as
Bitcoin’s value rises.
For example, if 1 sat = $1 someday, having 100 outputs worth <1,000 sats
each would no longer represent spam — but rather normal payments.
By then, the TinyTx limit would already have adjusted down automatically.
Patterns this would limit
- Fake pubkeys or scripts used to embed data via many UTXOs
- Bitcoin STAMPS / UTXO-art spreading payloads across thousands of dust
outputs
- BRC-20 batch mints with 100s of "tiny" sat fan-outs
- Some Ordinal or state inscription schemes that distribute data across
many tiny outputs
- Dust bombing (UTXO tracking or chain spam)
- Mass micro-airdrops below the "tiny" sat range
These use cases rely on cheap, numerous outputs — making them several times
more costly under this rule.
Non-goals / unaffected
- Normal user transactions, LN channel opens, and multisig spends
- Batched exchange payouts (they typically have > 40% large-value
outputs)
- Single/few-output inscriptions using witness data (not affected)
- Any legitimate pattern where most outputs are above the threshold
Why a ratio and a count?
Requiring both (tiny_count >= 100) and (tiny_ratio >= 60%) helps avoid
false positives, such as legitimate custodial payouts or consolidation
transactions with mixed values.
It specifically filters transactions that are mostly dust, rather than
merely containing some.
Inquiry
- Are there credible, non-spam use cases that truly require >=100
sub-4k-sat outputs (or equivalent at later eras) and a >=60% tiny ratio?
- Could this affect fee market behavior or any privacy tools in
unintended ways?
- Any concern with the 100 tiny_count limit or 60% tiny_ratio?
- Any other unintended consequences?
- Any objections in general?? What are they?
Intent
This proposal doesn’t censor any monetary transaction or prevent
inscriptions; it simply prices storage according to resource cost.
It keeps the chain “light and nimble” for everyday payments while allowing
future flexibility — because the TinyTx definition decreases automatically
in line with halvings and Bitcoin’s long-term value growth.
CODE SKETCHES
(with minimal syntax highlighting here: https://pastebin.com/9qdQCH83)
RELAY POLICY FILTER sketch —
// Place in src/policy/policy.cpp, and call from within IsStandardTx()
before returning: // if (IsBulkDust(tx, reason)) // return false; // reject
as nonstandard //
==========================================================================================================
bool IsBulkDust(const CTransaction& tx, std::string& reason) { static
constexpr int MAX_TINY_OUTPUTS = 100; // >=100 tiny outputs triggers ratio
check static constexpr double TINY_RATIO_THRESHOLD = 0.6; // >=60% of all
outputs tiny → reject static constexpr CAmount BASE_TINY_THRESHOLD = 4096;
// starting tiny threshold (sats) static constexpr int64_t
FIRST_TINY_HALVING_H = 1260000; // first halving of tiny threshold static
constexpr int64_t HALVING_INTERVAL = 210000; // blocks per subsequent
halving static constexpr CAmount MIN_TINY_FLOOR = 1; // never below 1 sat
const int total = tx.vout.size(); if (total == 0) return false; int
currentHeight = chainActive.Tip() ? chainActive.Tip()->nHeight : 0; // Era
index for TinyTx threshold, anchored at FIRST_TINY_HALVING_H (not subsidy
eras) int era = 0; if (currentHeight >= FIRST_TINY_HALVING_H) { era = 1 +
static_cast<int>((currentHeight - FIRST_TINY_HALVING_H) /
HALVING_INTERVAL); } CAmount tinyThresh = BASE_TINY_THRESHOLD >> era; //
halve per era if (tinyThresh < MIN_TINY_FLOOR) tinyThresh = MIN_TINY_FLOOR;
int tiny = 0; for (const auto& out : tx.vout) { if (out.nValue <
tinyThresh) ++tiny; } if (tiny >= MAX_TINY_OUTPUTS &&
(static_cast<double>(tiny) / total) >= TINY_RATIO_THRESHOLD) { reason =
strprintf("too-many-tiny-outputs(%d of %d, %.2f%%, tiny<%d)", tiny, total,
100.0 * tiny / total, tinyThresh); return true; // flag as bulk dust
(nonstandard) } return false; }
CONSENSUS (soft-fork, hybrid activation) sketch —
// Helpers in src/consensus/tx_check.cpp; activation/enforcement in
src/validation.cpp // Also define deployment in: src/consensus/params.h,
src/chainparams.cpp, src/versionbits.* //
==========================================================================================================
// -----------------------------------------------------------------------
// --- In src/consensus/tx_check.cpp (helper only; no params needed) --- //
-----------------------------------------------------------------------
static constexpr CAmount BASE_TINY_THRESHOLD = 4096; static constexpr
int64_t FIRST_TINY_HALVING_H = 1260000; static constexpr int64_t
HALVING_INTERVAL = 210000; static constexpr int MAX_TINY_OUTPUTS = 100;
static constexpr double TINY_RATIO_THRESHOLD = 0.6; static constexpr
CAmount MIN_TINY_FLOOR = 1; bool IsBulkDust(const CTransaction& tx, int
currentHeight) // expose via tx_check.h if needed { const int total =
tx.vout.size(); if (total == 0) return false; int era = 0; if
(currentHeight >= FIRST_TINY_HALVING_H) { era = 1 +
static_cast<int>((currentHeight - FIRST_TINY_HALVING_H) /
HALVING_INTERVAL); } CAmount tinyThresh = BASE_TINY_THRESHOLD >> era; if
(tinyThresh < MIN_TINY_FLOOR) tinyThresh = MIN_TINY_FLOOR; int tiny = 0;
for (const auto& out : tx.vout) { if (out.nValue < tinyThresh) ++tiny; } if
(tiny >= MAX_TINY_OUTPUTS && (static_cast<double>(tiny) / total) >=
TINY_RATIO_THRESHOLD) return true; return false; } //
----------------------------------------------------------------------- //
--- In src/validation.cpp (enforcement with hybrid activation) --- //
-----------------------------------------------------------------------
#include <consensus/tx_check.h> #include <versionbits.h> const
Consensus::Params& params = chainparams.GetConsensus(); int currentHeight =
chainActive.Tip() ? chainActive.Tip()->nHeight : 0; const bool
bulk_dust_active = DeploymentActiveAtTip(params,
Consensus::DEPLOYMENT_BULK_DUST_LIMIT) || (currentHeight >=
params.BulkDustActivationHeight); if (bulk_dust_active) { if
(IsBulkDust(tx, currentHeight)) { return
state.Invalid(TxValidationResult::TX_CONSENSUS, "too-many-tiny-outputs"); }
} //
----------------------------------------------------------------------- //
--- In src/consensus/params.h --- //
-----------------------------------------------------------------------
enum DeploymentPos { // ... DEPLOYMENT_BULK_DUST_LIMIT,
MAX_VERSION_BITS_DEPLOYMENTS }; struct Params { // ... int
BulkDustActivationHeight; // height flag-day fallback }; //
----------------------------------------------------------------------- //
--- In src/chainparams.cpp (per-network values; examples only) --- //
-----------------------------------------------------------------------
consensus.vDeployments[Consensus::DEPLOYMENT_BULK_DUST_LIMIT].bit = 12;
consensus.vDeployments[Consensus::DEPLOYMENT_BULK_DUST_LIMIT].nStartTime =
1767225600; // 2026-01-01 UTC
consensus.vDeployments[Consensus::DEPLOYMENT_BULK_DUST_LIMIT].nTimeout =
1838160000; // 2028-04-01 UTC
consensus.vDeployments[Consensus::DEPLOYMENT_BULK_DUST_LIMIT].min_activation_height
= 969696; consensus.BulkDustActivationHeight = 1021021; // flag-day fallback
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next reply other threads:[~2025-10-30 0:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-30 0:03 Frenchanfry [this message]
2025-10-30 1:02 ` [bitcoindev] " Doctor Buzz
2025-10-30 14:14 ` Doctor Buzz
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