Bitcoin Core 0.15.0 Release Guide for Node Operators

This guide explains Bitcoin Core 0.15.0 release in plain English. It summarises the important changes, who they affect and what should be checked before an upgrade.

Chainstate conversion

The UTXO database changed from a per-transaction to per-output model. Conversion could take minutes and increased the on-disk database while improving cache behaviour and validation performance. Older releases could not read the new chainstate. Pruned nodes downgrading with reindex-chainstate might need to download and process the whole blockchain again, so rollback capacity had to be planned before first start.

Fee estimation

The estimator gained short, medium and long horizons, conservative and economical modes, targets up to 1,008 blocks and better handling of evicted transactions. The fee-estimate file format also changed and estimates were discarded across the version boundary. Integrations needed fallback behaviour for insufficient data and should record returned errors, target, mode and mempool conditions.

Multiwallet routing

Multiple wallets could be loaded, but wallet RPC calls needed the wallet-specific HTTP path or bitcoin-cli rpcwallet option. Node-level calls remained on the ordinary endpoint and listwallets exposed loaded names. The 0.15.0 interface was explicitly described as unstable. Automation must fail closed when a wallet is omitted rather than send from whichever wallet appears default.

RBF and coin-age policy

The GUI added opt-in RBF creation and fee bumping. Separately, Core removed coin-age priority, free-transaction relay and related configuration and RPC fields. Mining template and relay clients had to stop relying on priority deltas while retaining the dummy positional argument where required for compatibility. These were policy changes, not new consensus validity rules.

Mempool and new RPCs

The persistmempool switch controlled loading and saving mempool.dat, defaulting to true. New calls included abortrescan, combinerawtransaction, estimaterawfee, getchaintxstats, listwallets and uptime. Signrawtransaction no longer served as a transaction combiner. Contract tests should cover named arguments, return shapes, errors and state changes across restart.

Wallet recovery warnings

addwitnessaddress remained an expert testing call without guaranteed backup recovery. Encrypted HD wallet recovery could miss keys unless the wallet stayed unlocked long enough for keypool top-up and a rescan was triggered through the documented workaround. Seed ownership alone did not prove that every experimental derivation and imported script would be rediscovered.

How specialists test it

Node operators test the release on a representative non-production system. They check startup, normal operation, failure handling and restart before changing a live node. Connected wallets, monitoring and mining services should also be checked.

Conclusion

Bitcoin Core 0.15.0 was an operationally large release despite its familiar interface. Chainstate incompatibility, estimator changes and wallet routing required rehearsed upgrade and rollback procedures, not an in-place binary swap.