Persist the master node list periodically so an unclean exit doesn't cost the database - #224
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Three related logging defects made master node list failures undiagnosable.
blockchain.cpp used a fmt-style "{}" placeholder inside a stream-style MFATAL,
so the fatal error that stops the daemon printed a literal "{}" instead of the
block that failed:
Unable to process block {} for updating master node list: ...
crypto::hash has a non-explicit operator bool() and no fmt formatter, so
passing one to fmt::format silently selects the bool conversion and prints
"true". Seven call sites in master_node_list.cpp did this, including the
checkpoint verification failures, so they never identified a block either:
Failed to verify block components for incoming block true at height 5703039
They now go through tools::type_to_hex.
Finally, three of the paths where master_node_list::load() gives up returned
false without logging. Each one silently sends the daemon into a full rescan
from the hf9 height, so an operator had no way to tell why a start was slow.
master_node_list::store() was only called at the end of a subsystem rescan and in core::deinit(), so a daemon following the chain tip never wrote the list out until it was asked to shut down cleanly. Any unclean exit -- SIGKILL, OOM, power loss, or an assertion failure in a dependency -- therefore discarded every block of state accumulated since the process started. On the next launch load_missing_blocks_into_beldex_subsystems() then replays from wherever the last stored state left off. For a long-running daemon that is most of the chain: slow, and able to fail outright, in which case the daemon cannot start at all and the operator is left restoring the database by hand. Write the list from core::on_idle instead, at most once every five minutes and only when it has advanced, which bounds the replay after an unclean exit to a few blocks. The write takes the blockchain lock as well as the list lock and runs off the block handling path, matching cleanup_proofs(); store() is otherwise unchanged, so a clean shutdown behaves exactly as before. Verified by killing a synced master node with SIGKILL and no grace period: an unpatched daemon failed its replay and had to rebuild from a snapshot, while a checkpointing one restarted with its chain intact.
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WalkthroughThe change parallelizes transaction loading during blockchain subsystem rescans and adds periodic short-term master-node list persistence. It also refactors state serialization, tracks persisted height across lifecycle operations, and improves block-hash error logging. ChangesRescan and checkpointing
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to This change adds bounded periodic master-node state checkpoints and faster rescan transaction loading while preserving full archive writes for shutdown and rescan paths. No concrete merge-blocking risk remains. Sequence Diagram(s)Parallel transaction loadingsequenceDiagram
participant Rescan as load_missing_blocks_into_beldex_subsystems
participant ThreadPool
participant Loader as _get_transactions
participant BlockchainDB
Rescan->>ThreadPool: submit transaction loads for each chunk
ThreadPool->>Loader: deserialize transactions
Loader->>BlockchainDB: fetch transaction blobs
BlockchainDB-->>Loader: return transaction data
Loader-->>ThreadPool: return load result
ThreadPool-->>Rescan: continue block processing
Periodic master-node checkpointsequenceDiagram
participant CoreIdle as core::on_idle
participant Checkpoint as master_node_list::checkpoint_state
participant Store as master_node_list::store(false)
participant MasterNodeDB
CoreIdle->>Checkpoint: invoke periodic checkpoint
Checkpoint->>Store: persist state when height advances
Store->>MasterNodeDB: write short-term state
MasterNodeDB-->>Store: return write result
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🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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🟡 Changes recommended
It introduces a publicly exposed non-locking transactions API and reduces failure diagnostics in a critical rescan path unless the requested adjustments are made.
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Pull request overview
This PR improves master node operational resilience by periodically persisting the master node list (to limit replay after unclean shutdown), while also reducing the memory spike of master node list persistence and improving diagnostic logging during rescan/startup.
Changes:
- Add periodic
core::on_idlecheckpointing of the master node list state (bounded-frequency, only when advanced) to mitigate data loss from unclean exits. - Refactor master node list persistence to optionally skip long-term archive serialization (for periodic checkpoints) and reduce peak memory/copies during DB writes, with size/time logging.
- Parallelize transaction deserialization during subsystem rescan and improve several error/log messages to include actionable details.
File summaries
| File | Description |
|---|---|
| src/cryptonote_core/master_node_list.h | Extends the persistence API to optionally skip the archive and adds checkpoint-related state tracking. |
| src/cryptonote_core/master_node_list.cpp | Implements periodic checkpointing, archive-skipping store path, reduced-copy serialization/write, and improved hash/log output. |
| src/cryptonote_core/cryptonote_core.h | Adds a new periodic task timer for checkpointing the master node list. |
| src/cryptonote_core/cryptonote_core.cpp | Hooks the new periodic checkpoint task into core::on_idle. |
| src/cryptonote_core/blockchain.h | Adds a non-locking transaction retrieval method used for parallel rescan work. |
| src/cryptonote_core/blockchain.cpp | Holds the blockchain lock during rescan, parallelizes tx loading per chunk, and improves fatal error reporting during rescan. |
Review details
- Files reviewed: 6/6 changed files
- Comments generated: 2
- Review effort level: Lite
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load_missing_blocks_into_beldex_subsystems() fetched each block's transactions one block at a time, on the same thread that then applies the master node list and BNS updates. Deserialising those transactions dominates the scan: the progress line typically reported around two seconds of subsystem work per ten second window, with the rest spent loading and parsing. Transaction loading is independent per block, so hand a whole chunk to the thread pool and keep the subsystem updates strictly sequential afterwards. This mirrors how oxen-core loads blocks for the same scan. Doing so needs a non-locking accessor: get_transactions() takes the blockchain lock, so calling it from several workers would serialise them again. Split it into a locking wrapper and _get_transactions(), and have the scan hold the blockchain lock for its whole duration instead. The lock is recursive, so this is safe when a caller already holds it (pop_blocks does). The LMDB layer gives each thread its own read transaction, so concurrent reads are fine. The progress and summary lines now also report time spent loading transactions, so the split between loading and subsystem work is visible.
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Actionable comments posted: 1
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Inline comments:
In `@src/cryptonote_core/master_node_list.cpp`:
- Line 2202: Update blockchain_detached() to set
m_transient.state_added_to_archive to true at the point where
m_transient.state_archive’s tail is erased, ensuring subsequent
checkpoint_state() and store() persist the truncated archive.
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src/cryptonote_core/blockchain.cppsrc/cryptonote_core/blockchain.hsrc/cryptonote_core/cryptonote_core.cppsrc/cryptonote_core/cryptonote_core.hsrc/cryptonote_core/master_node_list.cppsrc/cryptonote_core/master_node_list.h
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The periodic checkpoint called store() unchanged, which serialises the long-term state archive whenever it is dirty. That archive grows without bound -- hundreds of MB and >100k historical states on mainnet -- and the ostringstream/str()/append sequence transiently needs several times its size. On a memory-capped node that spike is fatal: a fleet of 2GB containers running the 5 minute checkpoint was OOM-killed repeatedly, with the kernel reporting anon-rss exactly at the limit. It is also reachable on a schedule rather than rarely. process_block() marks the archive dirty for 246 of every 10000 heights, and continuously while a node is catching up -- which is precisely when a freshly bootstrapped node is already at its memory ceiling. Give store() an include_archive parameter, default true, and have only the periodic caller pass false. The dirty flag is then left set so the next full store() -- end of rescan, or core::deinit() -- still writes the archive. The three existing callers are unchanged, so shutdown and rescan behaviour is identical. Recovery is unaffected: load() restores m_state from the short-term blob and never from the archive. Also fix two things found alongside it: blockchain_detached() moved m_state backwards without clearing m_last_stored_height, so checkpoint_state()'s guard suppressed every write until the chain climbed back past the old high-water mark. A state written for an abandoned fork could survive at the same height and be reloaded on the next start. Clear the mark on detach. Reduce the rescan chunk from 1000 blocks to 200. Now that a chunk's transactions are parsed up front and held together, the chunk size bounds the peak allocation of the scan; oxen-core uses 50 for the same reason.
store() built the serialised blob through three live copies: the archiver's ostringstream buffer, the string that str() returns, and a member string that append() copied it into again -- all held simultaneously, on top of the already-materialised serialisation cache. For the long-term archive, which is 582MB and ~139k states on a mainnet node, that is well over a gigabyte of transient allocation, and it is what pushed 2GB nodes into swap and then into the OOM killer. Scope the archiver so its buffer is released before the database write, move the blob out instead of appending it, and drop the serialisation cache once the bytes exist. The blob is now a local, so nothing survives the call. The member it replaces, cache_data_blob, was worse than an extra copy: clear() does not release capacity, so after one archive write every node held the archive's full size in string capacity for the rest of the process's life. Also log the size and duration of each write. Until now the only way to find out what a store() cost was to measure the gap between two unrelated log lines.
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Blockchain::init() runs the detach hooks at the current tip on every start. Nothing has actually been detached there -- the call exists to drive the subsystem rescan -- but blockchain_detached() treated it as a real reorg. The list that load() restores always trails the tip, because store() only serialises states up to the short-term cull window, so the revert target was never present in state_history. That sent the function to its fallback, which rewinds to the previous STORE_LONG_TERM_STATE_INTERVAL boundary and discards every state since: up to 10k blocks of valid work thrown away on a clean restart. The replay that followed was not merely slow. It re-verifies state change votes against quorums it rebuilds as it goes, and one block it cannot re-verify aborts startup with "Failed to start core". On mainnet a node restarting while that boundary sat below height 5722157 could not start at all, and recovered only by discarding its chain and resyncing. Return early when the list is already at or behind the revert point. A clean restart now rescans ~1.2k blocks in about 3s rather than ~9.3k and failing.
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Added one more commit: While soak-testing the earlier commits on mainnet I found that a clean restart was rescanning far more than it should, and on some nodes failing to start at all.
That is up to 10k blocks of valid state thrown away on an ordinary restart. The replay that follows is not merely slow: it re-verifies state change votes against quorums it rebuilds as it goes, and a single block it cannot re-verify aborts startup with Measured on a mainnet node at height ~5729356, restarting cleanly: I reproduced the startup failure on five separate nodes, including one whose database had just been rebuilt from a fresh sync, and confirmed the fix over two consecutive restarts. Unpatched v7.0.3 fails identically at the same block, so this is not a regression introduced by the earlier commits in this PR — but those commits do not help until this one is in, because the rollback discards the state they persist. |
A master node that exits uncleanly loses its master node list and cannot always rebuild it, which costs the operator the whole database. These five commits address that, plus the logging that made it hard to diagnose.
Found while running a large fleet of master nodes in memory-capped containers, where unclean exits (OOM kills, crashes) are the normal way a node stops.
The problem
master_node_list::store()is only called at the end of a subsystem rescan and incore::deinit(). A daemon following the chain tip therefore never writes the list out until it is asked to shut down cleanly. Any unclean exit discards every block of state accumulated since the process started.On the next launch
load_missing_blocks_into_beldex_subsystems()replays from wherever the last stored state left off. For a long-running daemon that is most of the chain — slow, and able to fail outright:It does not self-heal — each restart re-scans from the hf9 height and fails at the same block.
The fix
checkpoint_state()writes the list fromcore::on_idleat most every five minutes, and only when it has advanced. That bounds the replay after an unclean exit to a few blocks. It takes the blockchain lock as well as the list lock and runs off the block-handling path, matchingcleanup_proofs();store()itself is unchanged, so a clean shutdown behaves exactly as before.Two things had to come with it:
The periodic write must not serialise the long-term archive. The archive grows without bound — 582MB and ~139k states on a node we measured — and the
ostringstream/str()/appendsequence transiently needs several times that. Putting it on a five-minute timer OOM-killed a fleet of 2GB containers, with the kernel reportinganon-rssexactly at the limit.store()now takes aninclude_archiveparameter; only the periodic caller passesfalse, leaving the dirty flag set so the next fullstore()still writes it. Measured cost of the periodic write afterwards: 1.66 MB in 0.05s.blockchain_detached()must clear the high-water mark. It movesm_statebackwards without touchingm_last_stored_height, so the guard incheckpoint_state()suppressed every write until the chain climbed back past the old height — and a state written for an abandoned fork could survive at the same height and be reloaded on the next start.Also here
Error messages that never identified anything.
blockchain.cpp:379used a fmt-style{}inside a stream-styleMFATAL, so the fatal error that stops the daemon printed a literal{}. Separately,crypto::hashhas a non-explicitoperator bool()and no fmt formatter, so passing one tofmt::formatsilently selects the bool conversion:Seven call sites in
master_node_list.cppdid this, including both checkpoint-verification failures. They now go throughtools::type_to_hex. Three paths whereload()gives up also returnedfalsewithout logging; each sends the daemon into a full rescan, so an operator had no way to tell why a start was slow.Memory profile of the write. The blob was built through three live copies — the archiver's buffer, the string
str()returns, and a member stringappend()copied it into again — all held at once. The member (cache_data_blob) was worse than an extra copy:clear()does not release capacity, so after one archive write every node held the archive's full size in string capacity for the rest of the process's life. Each write now also logs its size and duration.Parallel transaction loading during the rescan (
26bdba8dd), mirroring how oxen-core loads blocks for the same scan. This one is offered for your judgement rather than asserted: it is correct as far as we can tell and has run without incident, but we were unable to produce a before/after measurement, because the checkpointing above largely removes the long rescans it would speed up. Drop it if you would rather not take an unmeasured change.Testing
Built and run on a 26-node mainnet master node fleet in 2GB containers.
docker restart,docker kill(no grace), a 2000-blockpop_blocks, and an accidental SIGKILL of 24 nodes at once — 0 chain losses in every case.One caveat worth stating: our nodes run a pruned blockchain, which is not officially supported for master nodes. The unclean-exit failure and the memory behaviour both reproduce independently of pruning, but our replay failures were observed on pruned nodes.