Stop enforcing descendant size/count limits
What changed, and why it matters
This Bitcoin Core commit removes enforcement of two older mempool limits—how many child transactions and how much total data can descend from a single transaction—and relies instead on newer 'cluster' limits. The change is described by the project as a simplification, not a security fix. It could alter how large transaction chains are rejected, but the diff itself does not show a vulnerability or emergency patch.
Treat as a normal consensus-adjacent mempool policy change. Review whether removing per-transaction descendant limits could allow unexpectedly large clusters or DoS-shaped transaction graphs under the new cluster-limit regime. Monitor release notes and upstream discussion for any follow-up fixes.
Security signals we found
removal of mempool admission limits
change in transaction package rejection semantics
test expectations shifted from descendant-limit errors to cluster-limit errors
Evidence from the diff
The patch deletes the descendant_count and descendant_size_vbytes checks from CTxMemPool::CalculateAncestorsAndCheckLimits and CTxMemPool::CheckPackageLimits. It also updates functional tests to expect ‘too-large-cluster’ errors instead of ‘too-long-mempool-chain’ or ‘package-mempool-limits’ errors, and switches test configurations from -limitdescendantcount/-limitdescendantsize to -limitclustercount/-limitclustersize. The stated rationale is that cluster size limits are sufficient.
Changed components
src/txmempool.cppmempool transaction admission logicpackage validation (testmempoolaccept / submitpackage)TRUC (v3 transaction) mempool testsInspect captured patch +26 / −78
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index ce9218f9..ab6d3ed2 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -177,12 +177,6 @@ util::Result<CTxMemPool::setEntries> CTxMemPool::CalculateAncestorsAndCheckLimit
ancestors.insert(stageit);
staged_ancestors.erase(stage);
- if (stageit->GetSizeWithDescendants() + entry_size > limits.descendant_size_vbytes) {
- return util::Error{Untranslated(strprintf("exceeds descendant size limit for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limits.descendant_size_vbytes))};
- } else if (stageit->GetCountWithDescendants() + entry_count > static_cast<uint64_t>(limits.descendant_count)) {
- return util::Error{Untranslated(strprintf("too many descendants for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limits.descendant_count))};
- }
-
const CTxMemPoolEntry::Parents& parents = stageit->GetMemPoolParentsConst();
for (const CTxMemPoolEntry& parent : parents) {
txiter parent_it = mapTx.iterator_to(parent);
@@ -200,15 +194,6 @@ util::Result<CTxMemPool::setEntries> CTxMemPool::CalculateAncestorsAndCheckLimit
util::Result<void> CTxMemPool::CheckPackageLimits(const Package& package,
const int64_t total_vsize) const
{
- size_t pack_count = package.size();
-
- // Package itself is busting mempool limits; should be rejected even if no staged_ancestors exist
- if (pack_count > static_cast<uint64_t>(m_opts.limits.descendant_count)) {
- return util::Error{Untranslated(strprintf("package count %u exceeds descendant count limit [limit: %u]", pack_count, m_opts.limits.descendant_count))};
- } else if (total_vsize > m_opts.limits.descendant_size_vbytes) {
- return util::Error{Untranslated(strprintf("package size %u exceeds descendant size limit [limit: %u]", total_vsize, m_opts.limits.descendant_size_vbytes))};
- }
-
CTxMemPoolEntry::Parents staged_ancestors;
for (const auto& tx : package) {
for (const auto& input : tx->vin) {
diff --git a/test/functional/feature_rbf.py b/test/functional/feature_rbf.py
index 81ecef54..0590af12 100755
--- a/test/functional/feature_rbf.py
+++ b/test/functional/feature_rbf.py
@@ -27,15 +27,6 @@ MAX_CLUSTER_LIMIT = 64
class ReplaceByFeeTest(BitcoinTestFramework):
def set_test_params(self):
self.num_nodes = 2
- self.extra_args = [
- [
- "-limitancestorcount=64",
- "-limitdescendantcount=64",
- ],
- # second node has default mempool parameters
- [
- ],
- ]
self.uses_wallet = None
def run_test(self):
diff --git a/test/functional/mempool_package_limits.py b/test/functional/mempool_package_limits.py
index 5e402ede..3f267779 100755
--- a/test/functional/mempool_package_limits.py
+++ b/test/functional/mempool_package_limits.py
@@ -15,7 +15,7 @@ from test_framework.wallet import MiniWallet
# 2) run the subtest, which may submit some transaction(s) to the mempool and
# create a list of hex transactions
# 3) testmempoolaccept the package hex and check that it fails with the error
-# "package-mempool-limits" for each tx
+# "too-large-cluster" for each tx
# 4) after mining a block, clearing the pre-submitted transactions from mempool,
# check that submitting the created package succeeds
def check_package_limits(func):
@@ -26,7 +26,7 @@ def check_package_limits(func):
testres_error_expected = node.testmempoolaccept(rawtxs=package_hex)
assert_equal(len(testres_error_expected), len(package_hex))
for txres in testres_error_expected:
- assert "package-mempool-limits" in txres["package-error"]
+ assert "too-large-cluster" in txres["package-error"]
# Clear mempool and check that the package passes now
self.generate(node, 1)
@@ -39,6 +39,7 @@ class MempoolPackageLimitsTest(BitcoinTestFramework):
def set_test_params(self):
self.num_nodes = 1
self.setup_clean_chain = True
+ self.extra_args = [["-limitclustercount=25"]]
def run_test(self):
self.wallet = MiniWallet(self.nodes[0])
diff --git a/test/functional/mempool_packages.py b/test/functional/mempool_packages.py
index 74d04f07..9cf1aa01 100755
--- a/test/functional/mempool_packages.py
+++ b/test/functional/mempool_packages.py
@@ -7,19 +7,18 @@
from decimal import Decimal
from test_framework.messages import (
- DEFAULT_DESCENDANT_LIMIT,
DEFAULT_CLUSTER_LIMIT,
)
from test_framework.p2p import P2PTxInvStore
from test_framework.test_framework import BitcoinTestFramework
from test_framework.util import (
assert_equal,
- assert_raises_rpc_error,
)
from test_framework.wallet import MiniWallet
# custom limits for node1
-CUSTOM_DESCENDANT_LIMIT = 11
+CUSTOM_CLUSTER_LIMIT = 10
+assert CUSTOM_CLUSTER_LIMIT < DEFAULT_CLUSTER_LIMIT
class MempoolPackagesTest(BitcoinTestFramework):
def set_test_params(self):
@@ -30,7 +29,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
[
],
[
- "-limitdescendantcount={}".format(CUSTOM_DESCENDANT_LIMIT),
+ "-limitclustercount={}".format(CUSTOM_CLUSTER_LIMIT),
],
]
@@ -40,8 +39,8 @@ class MempoolPackagesTest(BitcoinTestFramework):
peer_inv_store = self.nodes[0].add_p2p_connection(P2PTxInvStore()) # keep track of invs
- # DEFAULT_DESCENDANT_LIMIT transactions off a confirmed tx should be fine
- chain = self.wallet.create_self_transfer_chain(chain_length=DEFAULT_DESCENDANT_LIMIT)
+ # DEFAULT_CLUSTER_LIMIT transactions off a confirmed tx should be fine for default node
+ chain = self.wallet.create_self_transfer_chain(chain_length=DEFAULT_CLUSTER_LIMIT)
witness_chain = [t["wtxid"] for t in chain]
ancestor_vsize = 0
ancestor_fees = Decimal(0)
@@ -55,22 +54,18 @@ class MempoolPackagesTest(BitcoinTestFramework):
# Otherwise, getrawmempool may be inconsistent with getmempoolentry if unbroadcast changes in between
peer_inv_store.wait_for_broadcast(witness_chain)
- # Check mempool has DEFAULT_DESCENDANT_LIMIT transactions in it, and descendant and ancestor
+ # Check mempool has DEFAULT_CLUSTER_LIMIT transactions in it, and descendant and ancestor
# count and fees should look correct
mempool = self.nodes[0].getrawmempool(True)
- assert_equal(len(mempool), DEFAULT_DESCENDANT_LIMIT)
+ assert_equal(len(mempool), DEFAULT_CLUSTER_LIMIT)
descendant_count = 1
descendant_fees = 0
descendant_vsize = 0
assert_equal(ancestor_vsize, sum([mempool[tx]['vsize'] for tx in mempool]))
- ancestor_count = DEFAULT_DESCENDANT_LIMIT
+ ancestor_count = DEFAULT_CLUSTER_LIMIT
assert_equal(ancestor_fees, sum([mempool[tx]['fees']['base'] for tx in mempool]))
- # Adding one more transaction on to the chain should fail.
- next_hop = self.wallet.create_self_transfer(utxo_to_spend=chain[-1]["new_utxo"])["hex"]
- assert_raises_rpc_error(-26, "too-long-mempool-chain", lambda: self.nodes[0].sendrawtransaction(next_hop))
-
descendants = []
ancestors = [t["txid"] for t in chain]
chain = [t["txid"] for t in chain]
@@ -186,23 +181,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
assert_equal(entry['fees']['modified'], entry['fees']['base'] + Decimal("0.00002"))
assert_equal(entry['fees']['descendant'], descendant_fees + Decimal("0.00002"))
- # Check that node1's mempool is as expected (-> custom ancestor limit)
- mempool0 = self.nodes[0].getrawmempool(False)
- mempool1 = self.nodes[1].getrawmempool(False)
- assert_equal(len(mempool1), CUSTOM_DESCENDANT_LIMIT)
- assert set(mempool1).issubset(set(mempool0))
- for tx in chain[:CUSTOM_DESCENDANT_LIMIT]:
- assert tx in mempool1
- entry0 = self.nodes[0].getmempoolentry(tx)
- entry1 = self.nodes[1].getmempoolentry(tx)
- assert not entry0['unbroadcast']
- assert not entry1['unbroadcast']
- assert_equal(entry1['fees']['base'], entry0['fees']['base'])
- assert_equal(entry1['vsize'], entry0['vsize'])
- assert_equal(entry1['depends'], entry0['depends'])
-
# Now test descendant chain limits
-
tx_children = []
# First create one parent tx with 10 children
tx_with_children = self.wallet.send_self_transfer_multi(from_node=self.nodes[0], num_outputs=10)
@@ -211,7 +190,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
# Sign and send up to MAX_DESCENDANT transactions chained off the parent tx
chain = [] # save sent txs for the purpose of checking node1's mempool later (see below)
- for _ in range(DEFAULT_DESCENDANT_LIMIT - 1):
+ for _ in range(DEFAULT_CLUSTER_LIMIT - 1):
utxo = transaction_package.pop(0)
new_tx = self.wallet.send_self_transfer_multi(from_node=self.nodes[0], num_outputs=10, utxos_to_spend=[utxo])
txid = new_tx["txid"]
@@ -221,22 +200,16 @@ class MempoolPackagesTest(BitcoinTestFramework):
transaction_package.extend(new_tx["new_utxos"])
mempool = self.nodes[0].getrawmempool(True)
- assert_equal(mempool[parent_transaction]['descendantcount'], DEFAULT_DESCENDANT_LIMIT)
+ assert_equal(mempool[parent_transaction]['descendantcount'], DEFAULT_CLUSTER_LIMIT)
assert_equal(sorted(mempool[parent_transaction]['spentby']), sorted(tx_children))
for child in tx_children:
assert_equal(mempool[child]['depends'], [parent_transaction])
- # Sending one more chained transaction will fail
- next_hop = self.wallet.create_self_transfer(utxo_to_spend=transaction_package.pop(0))["hex"]
- assert_raises_rpc_error(-26, "too-long-mempool-chain", lambda: self.nodes[0].sendrawtransaction(next_hop))
-
# Check that node1's mempool is as expected, containing:
- # - txs from previous ancestor test (-> custom ancestor limit)
# - parent tx for descendant test
# - txs chained off parent tx (-> custom descendant limit)
- self.wait_until(lambda: len(self.nodes[1].getrawmempool()) ==
- 2*CUSTOM_DESCENDANT_LIMIT, timeout=10)
+ self.wait_until(lambda: len(self.nodes[1].getrawmempool()) == 2*CUSTOM_CLUSTER_LIMIT, timeout=10)
mempool0 = self.nodes[0].getrawmempool(False)
mempool1 = self.nodes[1].getrawmempool(False)
assert set(mempool1).issubset(set(mempool0))
@@ -247,7 +220,7 @@ class MempoolPackagesTest(BitcoinTestFramework):
entry1 = self.nodes[1].getmempoolentry(tx)
assert not entry0['unbroadcast']
assert not entry1['unbroadcast']
- assert entry1["descendantcount"] <= CUSTOM_DESCENDANT_LIMIT
+ assert entry1["descendantcount"] <= CUSTOM_CLUSTER_LIMIT
assert_equal(entry1['fees']['base'], entry0['fees']['base'])
assert_equal(entry1['vsize'], entry0['vsize'])
assert_equal(entry1['depends'], entry0['depends'])
diff --git a/test/functional/mempool_sigoplimit.py b/test/functional/mempool_sigoplimit.py
index 965f9a5c..3b2d7373 100755
--- a/test/functional/mempool_sigoplimit.py
+++ b/test/functional/mempool_sigoplimit.py
@@ -169,14 +169,14 @@ class BytesPerSigOpTest(BitcoinTestFramework):
assert_equal(parent_individual_testres["vsize"], max_multisig_vsize)
# But together, it's exceeding limits in the *package* context. If sigops adjusted vsize wasn't being checked
- # here, it would get further in validation and give too-long-mempool-chain error instead.
+ # here, it would get further in validation and give too-large-cluster error instead.
packet_test = self.nodes[0].testmempoolaccept([tx_parent.serialize().hex(), tx_child.serialize().hex()])
- expected_package_error = f"package-mempool-limits, package size {2*max_multisig_vsize} exceeds descendant size limit [limit: 101000]"
+ expected_package_error = "too-large-cluster"
assert_equal([x["package-error"] for x in packet_test], [expected_package_error] * 2)
- # When we actually try to submit, the parent makes it into the mempool, but the child would exceed ancestor vsize limits
+ # When we actually try to submit, the parent makes it into the mempool, but the child would exceed cluster vsize limits
res = self.nodes[0].submitpackage([tx_parent.serialize().hex(), tx_child.serialize().hex()])
- assert "too-long-mempool-chain" in res["tx-results"][tx_child.wtxid_hex]["error"]
+ assert "too-large-cluster" in res["tx-results"][tx_child.wtxid_hex]["error"]
assert tx_parent.txid_hex in self.nodes[0].getrawmempool()
# Transactions are tiny in weight
diff --git a/test/functional/mempool_truc.py b/test/functional/mempool_truc.py
index 687b7072..6ba8cbff 100755
--- a/test/functional/mempool_truc.py
+++ b/test/functional/mempool_truc.py
@@ -196,15 +196,15 @@ class MempoolTRUC(BitcoinTestFramework):
node.invalidateblock(block["hash"])
self.check_mempool([tx_v3_block["txid"], tx_v2_block["txid"], tx_v3_block2["txid"], tx_v2_from_v3["txid"], tx_v3_from_v2["txid"], tx_v3_child_large["txid"], tx_chain_1["txid"], tx_chain_2["txid"], tx_chain_3["txid"], tx_chain_4["txid"]])
- @cleanup(extra_args=["-limitdescendantsize=10"])
+ @cleanup(extra_args=["-limitclustercount=1"])
def test_nondefault_package_limits(self):
"""
- Max standard tx size + TRUC rules imply the ancestor/descendant rules (at their default
+ Max standard tx size + TRUC rules imply the cluster rules (at their default
values), but those checks must not be skipped. Ensure both sets of checks are done by
- changing the ancestor/descendant limit configurations.
+ changing the cluster limit configurations.
"""
node = self.nodes[0]
- self.log.info("Test that a decreased limitdescendantsize also applies to TRUC child")
+ self.log.info("Test that a decreased cluster count limit also applies to TRUC child")
parent_target_vsize = 9990
child_target_vsize = 500
tx_v3_parent_large1 = self.wallet.send_self_transfer(
@@ -218,12 +218,11 @@ class MempoolTRUC(BitcoinTestFramework):
version=3
)
- # Parent and child are within v3 limits, but parent's 10kvB descendant limit is exceeded
+ # Parent and child are within v3 limits, but cluster count limit is exceeded.
assert_greater_than_or_equal(TRUC_MAX_VSIZE, tx_v3_parent_large1["tx"].get_vsize())
assert_greater_than_or_equal(TRUC_CHILD_MAX_VSIZE, tx_v3_child_large1["tx"].get_vsize())
- assert_greater_than(tx_v3_parent_large1["tx"].get_vsize() + tx_v3_child_large1["tx"].get_vsize(), 10000)
- assert_raises_rpc_error(-26, f"too-long-mempool-chain, exceeds descendant size limit for tx {tx_v3_parent_large1['txid']}", node.sendrawtransaction, tx_v3_child_large1["hex"])
+ assert_raises_rpc_error(-26, "too-large-cluster", node.sendrawtransaction, tx_v3_child_large1["hex"])
self.check_mempool([tx_v3_parent_large1["txid"]])
assert_equal(node.getmempoolentry(tx_v3_parent_large1["txid"])["descendantcount"], 1)
self.generate(node, 1)
diff --git a/test/functional/mempool_updatefromblock.py b/test/functional/mempool_updatefromblock.py
index 6ee31ffa..bf0b8778 100755
--- a/test/functional/mempool_updatefromblock.py
+++ b/test/functional/mempool_updatefromblock.py
@@ -27,8 +27,7 @@ CUSTOM_DESCENDANT_COUNT = CUSTOM_ANCESTOR_COUNT
class MempoolUpdateFromBlockTest(BitcoinTestFramework):
def set_test_params(self):
self.num_nodes = 1
- # Ancestor and descendant limits depend on transaction_graph_test requirements
- self.extra_args = [['-limitdescendantsize=1000', '-limitancestorsize=1000', f'-limitancestorcount={CUSTOM_ANCESTOR_COUNT}', f'-limitdescendantcount={CUSTOM_DESCENDANT_COUNT}', "-limitclustersize=1000"]]
+ self.extra_args = [['-limitclustersize=1000']]
def create_empty_fork(self, fork_length):
'''
Why this scored 32/100
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