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Merge bitcoin/bitcoin#34636: node: allocate index caches proportional to usage patterns

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5a2e359213 clarify blockfilterindex cache allocation rationale (Sebastian van Staa)
d06dabf26b node: allocate index caches proportional to usage patterns (Sebastian van Staa)

Pull request description:

  The current cache allocation for optional indexes (txindex, txospenderindex, blockfilterindex) uses a sequential total_cache / 8 approach where each index gets 1/8 of the remaining budget after the previous index has been allocated. This means the order in which indexes appear in the code silently determines how much cache each one gets.

  |Index|Current share of total|
  |---|---|
  |txindex|~12%|
  |txospenderindex|~11%|
  |blockfilterindex|~10%|

  This is unintuitive, undocumented, and probably doesn't reflect actual usage patterns. This PR replaces the sequential 1/8 allocation with explicit percentages based on how the indexes are typically used. The current values are an educated guess, and subject to further benchmark and research of typical client usage patterns.

  |Index|Allocation|Rationale|
  |---|---|---|
  |txindex |10% |Serves getrawtransaction RPCs with mostly unique lookups across the entire blockchain: low cache reuse|
  |txospenderindex|5%|Serves gettxspendingprevout RPCs with very specific outpoint queries: likely the least repetitive access pattern|
  |blockfilterindex|5%|Serves BIP 157 light clients that repeatedly query the same recent blocks: highest cache benefit|

  UPDATE: blockfilterindex allocation changed from 15% to 5% in the course of the discussion

  This is a continuation of  the related discussion: https://github.com/bitcoin/bitcoin/pull/24539#discussion_r2809088034 and https://github.com/bitcoin/bitcoin/pull/31483.

  Further feedback and input is very much appreciated.

ACKs for top commit:
  fjahr:
    ACK 5a2e359213
  rustaceanrob:
    ACK 5a2e359213
  achow101:
    ACK 5a2e359213
  sedited:
    ACK 5a2e359213

Tree-SHA512: 69be2b0c274b975da58aef2513c3042be8a4c8acf0a86af86b962d4ebfd8cf90bcb1d9251d53995652b4825d0d1da24aabe92cdada9148c627690f8ad2ad8a29
This commit is contained in:
Ava Chow
2026-06-10 14:24:06 -07:00
parent 8598ec2204 5a2e359213
commit 530e1f5290
1 changed files with 16 additions and 5 deletions
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21
src/node/caches.cpp
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@@ -58,16 +58,27 @@ CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
{
size_t total_cache{CalculateDbCacheBytes(args)};
// Allocate proportional to usage pattern benefit:
// - txindex (10%): serves getrawtransaction RPCs with mostly unique,
// non-repetitive lookups across the entire blockchain.
// - blockfilterindex (5%): serves BIP 157 light clients that repeatedly
// query recent blocks, benefiting from LevelDB cache, but the
// working set for a typical 2-week offline gap is ~200kiB, well within 5%
// of the total cache.
// - txospenderindex (5%): serves gettxspendingprevout RPCs with very
// specific, rarely repeated outpoint queries.
// - coinstatsindex: intentionally not included here, since usage pattern
// does not seem to suggest it would be necessary to cache.
IndexCacheSizes index_sizes;
index_sizes.tx_index = std::min(total_cache / 8, args.GetBoolArg("-txindex", DEFAULT_TXINDEX) ? MAX_TX_INDEX_CACHE : 0);
total_cache -= index_sizes.tx_index;
index_sizes.txospender_index = std::min(total_cache / 8, args.GetBoolArg("-txospenderindex", DEFAULT_TXOSPENDERINDEX) ? MAX_TXOSPENDER_INDEX_CACHE : 0);
total_cache -= index_sizes.txospender_index;
index_sizes.tx_index = std::min(total_cache * 10 / 100, args.GetBoolArg("-txindex", DEFAULT_TXINDEX) ? MAX_TX_INDEX_CACHE : 0);
index_sizes.txospender_index = std::min(total_cache * 5 / 100, args.GetBoolArg("-txospenderindex", DEFAULT_TXOSPENDERINDEX) ? MAX_TXOSPENDER_INDEX_CACHE : 0);
if (n_indexes > 0) {
size_t max_cache = std::min(total_cache / 8, MAX_FILTER_INDEX_CACHE);
size_t max_cache = std::min(total_cache * 5 / 100, MAX_FILTER_INDEX_CACHE);
index_sizes.filter_index = max_cache / n_indexes;
total_cache -= index_sizes.filter_index * n_indexes;
}
total_cache -= index_sizes.tx_index;
total_cache -= index_sizes.txospender_index;
return {index_sizes, kernel::CacheSizes{total_cache}};
}