Bitcoin Core Indexes

Four optional indexes as of Bitcoin Core 31.1 (July 2026), in addition to the always-on UTXO set:

txindex

txindex=1

Maps every txid to its block / position. Enables:

• getrawtransaction <txid> for any historical tx (without txindex, only mempool + recent blocks since restart).

Cost:

• Disk: ~80 GB measured at height ~840,000 (April 2024), not re-measured since. It stores one LevelDB record per txid, so it scales with cumulative transaction count, not with block bytes: 991,029,144 transactions on 20 April 2024 vs 1,439,337,665 on 15 September 2026 (~45% more records), so budget roughly half again as much at the current tip (height 967,284, 16 September 2026).
• IBD time: +20-50% if enabled from start.
• Rebuild from scratch on a synced node: hours, not days.

When to enable:

• Block explorers / public APIs.
• Forensic / compliance tools.
• Apps that need to look up arbitrary historical txs.

When to skip:

• Pruned nodes (cannot combine).
• Node that only serves recent activity (mempool + last few blocks).

blockfilterindex (BIP157/158)

blockfilterindex=1
peerblockfilters=1   # serve filters to peers

Maintains compact block filters per block. Enables:

• getblockfilter <blockhash> RPC.
• Serving filters to BIP157 clients (Neutrino in LDK / btcwallet).
• Used by Electrs for fast scan operations.

Cost:

• Disk: ~6 GB total (same April 2024 measurement). One filter per block, so this one does scale with block data, which grew ~36% from ~566 GB on 20 April 2024 to ~769 GB on 15 September 2026.
• IBD impact: +5-10%.

When to enable:

• Running Electrs / Fulcrum / similar indexers (they need it).
• Lightning node using LDK / Neutrino backend.
• Provides scan service to lightweight clients.

coinstatsindex

coinstatsindex=1

Maintains rolling stats for gettxoutsetinfo (UTXO set value, count, hash) without a full scan.

Cost:

• Disk: ~1 GB.
• IBD impact: +2-5%.

When to enable:

• Frequent calls to gettxoutsetinfo (without it, the call takes minutes and locks the wallet).

Without it, gettxoutsetinfo still works but does a full scan on-demand → slow.

Upgrade note: Bitcoin Core 30.0 (October 2025) rewrote the index to fix an overflow bug, and the rewritten index syncs from scratch on the first start after the upgrade. It is stored at indexes/coinstatsindex/; the pre-30.0 index at indexes/coinstats/ is deliberately left in place for downgrades and must be deleted by hand to reclaim the space. Core logs a warning naming the old directory on every start while it exists.

txospenderindex

txospenderindex=1

Added in Bitcoin Core 31.0 (April 2026); default off. Records, for every non-coinbase input of every block transaction, which transaction spent that outpoint. Enables:

• gettxspendingprevout to answer for confirmed spends, not just mempool ones. With the index available the RPC also returns the blockhash of the spending block.

gettxspendingprevout gained two options in 31.0 alongside the index: mempool_only (defaults to true only when the index is unavailable; set false to fall through to the index) and return_spending_tx (returns the full spending tx as spendingtx).

Cost:

• Disk: the project publishes no figure. The index stores one LevelDB key per non-coinbase transaction input, so it scales with the cumulative input count of the chain, not with the UTXO set.

When to enable:

• Answering "what spent this output?" for arbitrary historical outpoints (explorers, forensics, watchtower-style tooling).

When to skip:

• Pruned nodes — bitcoind refuses to start ("Prune mode is incompatible with -txospenderindex").

Combining

All four can be enabled together. Pruning is incompatible with txindex and, since 31.0, with txospenderindex; blockfilterindex and coinstatsindex both work on a pruned node.

Typical configurations:

Rebuilding

Adding txindex=1 to existing node:

# Stop node
bitcoin-cli stop
# Edit conf, add txindex=1
# Restart; node rebuilds index
bitcoind -daemon
# Watch
tail -f ~/.bitcoin/debug.log

Output:

2025-... reindex-chainstate already=true txindex=true blockfilterindex=true coinstatsindex=true
2025-... Building txindex
... (hours later) ...
2025-... txindex is enabled

To force rebuild from scratch: -reindex (full reindex, days) or -reindex-chainstate (UTXO + indexes only, hours).

Index storage

Paths per doc/files.md at v31.1 (July 2026):

• <datadir>/indexes/txindex/ — LevelDB.
• <datadir>/indexes/txospenderindex/ — LevelDB (31.0+).
• <datadir>/indexes/blockfilter/basic/ — filter files, plus a db/ LevelDB alongside them.
• <datadir>/indexes/coinstatsindex/ — LevelDB (30.0+; the pre-30.0 index lived at indexes/coinstats/).

Common bugs

• Adding txindex=1 to a pruned node → bitcoind exits.
• Removing txindex from conf → bitcoind warns but continues with index "stuck"; manually delete indexes/txindex/ to free disk.
• Electrs/Fulcrum not connecting → check peerblockfilters=1 and blockfilterindex=1 are both set.
• Adding txospenderindex=1 to a pruned node → bitcoind exits, same as txindex.
• Upgrading past 30.0 and seeing disk usage jump → the old indexes/coinstats/ is still there next to the new indexes/coinstatsindex/; delete the old one once you are sure you will not downgrade to 29.x or lower.

See also

• operations/SKILL.md
• rpc/SKILL.md
• ../../infrastructure/electrs/SKILL.md
• ../../infrastructure/fulcrum/SKILL.md