bench: add WalletBalanceManySpent for high-history wallet scenario #34360

1. 
   w0xlt commented at 3:15 am on January 21, 2026: contributor

   This PR introduces a new benchmark that measures GetBalance() performance on wallets with extensive transaction history where the majority of outputs have already been spent.

   It was created to test #27865, which separates spent TXOs from spendable ones. This pattern mirrors real-world usage in high-activity wallets such as Lightning nodes, exchanges, hot wallets, and payment processors.

   Setup:

   • Creates 500 blocks × 100 coinbase outputs = 50,000 wallet TXOs
   • Matures all coinbases with COINBASE_MATURITY additional blocks
   • Spends 49,950 outputs in batched transactions (confirmed in blocks)
   • Consolidation outputs go to a burn script to avoid inflating wallet TXO count

   To keep the setup time reasonable, the benchmark uses the fast “fake block” approach, similar to wallet_create_tx.cpp.

2. bench: add WalletBalanceManySpent for high-history wallet scenario

   Add a benchmark that measures `GetBalance()` performance on wallets with
   extensive transaction history where most outputs have been spent.
   
   Scenario: 50,000 TXOs with 49,950 spent and 50 unspent.
   
   This pattern is common in high-activity wallets (Lightning nodes, exchange
   hot wallets, payment processors) and is the target scenario for optimizations
   that separate spent TXOs from spendable ones.
   
   Setup:
   - Creates 500 blocks × 100 coinbase outputs = 50,000 wallet TXOs
   - Matures all coinbases with COINBASE_MATURITY additional blocks
   - Spends 49,950 outputs in batched transactions (confirmed in blocks)
   - Consolidation outputs go to a burn script to avoid inflating wallet TXO count
   
   Introduces `src/bench/wallet_bench_util.h` with utilities for wallet
   benchmarks (TipBlock, GetTip, GenerateFakeBlock).

   42805a1609
3. DrahtBot added the label Tests on Jan 21, 2026
4. 
   DrahtBot commented at 3:15 am on January 21, 2026: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/34360.

   Reviews

   See the guideline for information on the review process. A summary of reviews will appear here.

   Conflicts

   No conflicts as of last run.

   LLM Linter (✨ experimental)

   Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

   • GenerateFakeBlock(params, test_setup->m_node, wallet, burn_script, 1) in src/bench/wallet_balance.cpp
   • GenerateFakeBlock(params, test_setup->m_node, wallet, burn_script, 1, 50 * COIN, block_txs) in src/bench/wallet_balance.cpp

   2026-01-21

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