feat: fee-ordered mempool eviction (TrimToSize/Expire) + displacement on admission

This fork never ported Bitcoin's mempool size-limiting: CTxMemPool had no TrimToSize/
Expire and LimitMempoolSize was commented out. An earlier commit added a blunt
DynamicMemoryUsage admission cap that bounded memory but bluntly REJECTED new txs when
full -- so a high-fee tx could not push out a low-fee one. This implements proper
fee-ordered eviction using the per-tx feerate index that already exists (mapTx index 1,
CompareTxMemPoolEntryByFee), with no new index and no descendant-tracking port.

- CTxMemPool::TrimToSize(sizelimit, pvNoSpendsRemaining): while DynamicMemoryUsage() is
  over the limit, evict the lowest-feerate tx (the tail of the feerate index) and its
  in-mempool descendants (recursive remove), re-deriving the tail each iteration.
  Terminates (pool strictly shrinks) and cleans every secondary index via remove().
- CTxMemPool::Expire(time): age-based sweep (entry time older than `time`), for
  LimitMempoolSize's -mempoolexpiry.
- LimitMempoolSize re-enabled (Expire + TrimToSize) and called from ConnectTip on every
  block connect. (No pcoinsTip->Uncache -- CCoinsViewCache has none in this fork; it is
  only a UTXO-cache perf hint.)
- AcceptToMemoryPool now ADDS the tx then TrimToSizes: a higher-fee tx displaces
  lower-fee ones; if this tx was itself the lowest-feerate (evicted), it is rejected
  ("mempool full"). Replaces the blunt reject-when-full cap.
- DEFAULT_MEMPOOL_EXPIRY 1 -> 72 hours (age-Expire is now live; 1h was too aggressive).

Known simplification (documented in code): per-tx feerate, not descendant-aggregate
(CPFP) scoring, and no rollingMinimumFeeRate anti-thrash. Adversarially reviewed
(termination, iterator safety, recursive-lock safety, index cleanup all confirmed) and
runtime-tested on the fleet: pool stays bounded under a 1600-tx flood, verifychain ok,
no hang/crash.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

This commit is contained in:

DanS

2026-07-09 09:01:06 +02:00

parent 1ec3dbfee3

commit adf2bacdbd

4 changed files with 64 additions and 14 deletions

									
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src/main.h
									
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				@@ -65,7 +65,7 @@ class CValidationState;

				class PrecomputedTransactionData;

				struct CNodeStateStats;

				#define DEFAULT_MEMPOOL_EXPIRY 1

				#define DEFAULT_MEMPOOL_EXPIRY 72 // hours; age-based Expire is now live via LimitMempoolSize -- was 1, too aggressive

				/** Default for -maxmempool, maximum megabytes of mempool memory usage */

				#define DEFAULT_MAX_MEMPOOL_SIZE 300

				#define _COINBASE_MATURITY 100

feat: fee-ordered mempool eviction (TrimToSize/Expire) + displacement on admission

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