Over the past two weeks, we worked on establishing a first baseline for the Consensus QTA (#1256). This work is also helping inform discussions with the Networking team about sync performance goals in general and for specific improvements, such as Genesis.
UTXO-HD was rebased atop main and the tests are passing.
Finally, the team has also worked to improve the Consensus layer's robustness and security.
BlockFetch for the syncing node (especially for Genesis).utxo-hd-9.1 branch, yielding positive results. The nodes function without errors. The memory and CPU usage is almost on par with the 9.1 node.utxo-hd-9.1 branch. If the tests pass, we will start working on wrapping up the documentation and preparing the branch for merging once it is decided to release this feature.
An issue was identified shortly before the Chang hard fork: it was found that ledger state snapshots would break ledger replay in the Conway era under mainnet conditions. The ledger and consensus teams worked rapidly to resolve the issue with a hotfix released within 24 hours of the hard fork. In order to avoid pauses in node availability, it was recommended that users should not restart their node process until they had upgraded their node to the hotfix - this included any node type: relays, block producers, DB-Sync nodes, etc.
The issue is documented here. The cause was a slight inconsistency between the ledger state snapshots that were written and those that could be read back; a side effect of the removal of pointer addresses in the Conway era. Nodes version 9.1.1 and later resolve this issue.
On 25th June 2025, a Cardano user inserted a series of transactions, each containing 194 large reference scripts onto the mainnet chain, funded from 3 wallets containing around 20K ada each. High deserialisation costs for these reference scripts impacted the node, resulting in network disruption to block producer nodes, an increase in network load, and some slowdown in transaction throughput.
The direct effect lasted about 12 hours until it was stopped by a community member, at a cost of 4603 ada to the user who had created the transactions. Overall, the network responded extemely well to the increased load, showing a high level of resilience, with some reduction in transaction throughput related to the overall high system load. The community response to the event was positive, praising the speed of response, the robustness of the Cardano network, the cohesion of the Cardano community, and its ability to diagnose and manage issues such as this.
The general issue had already been identified, and a mitigation (costing for reference scripts) had been prepared as part of the Chang hard fork, but not yet deployed to mainnet. Based on the event, stronger mitigations were prepared, including restricting large reference scripts, and changing the cost model. These mitigations were deployed via node versions 8.9.4, 8.12.1 or 8.12.2, and incorporated into node version 9.0.0 or later for the Chang hard fork.
We identified two issues relating to "blocks from the future".
While blocks from the near future have been known to occur on mainnet as a result of clock skew/misconfiguration, there are no known instances on mainnet of blocks from the far future. In both cases, restarting an affected node would resolve the issue.
A node considers a block to be from the future if its slot is ahead of the current slot. Ouroboros Praos mandates that all chains containing blocks from the future (at that time) are ignored during chain selection. As Praos assumes that all nodes have access to perfectly synchronized clocks, this will never cause nodes to disregard blocks that have been minted by other honest nodes. In an actual real-world deployment, this assumption is unrealistic due to the imperfections of protocols like NTP as well as leap seconds.
The issues that were identified meant that blocks from the future could potentially be used by malicious actors to create denial-of-service attacks.
Both issues were fixed by Cardano node 8.8 or later, and were eradicated at the Chang hard fork.