canton v3.5.6

Release of Canton 3.5.6

Canton 3.5.6 has been released on June 24, 2026.

Summary

This is a maintenance release that fixes an exceptional severe bug around logical synchronizer upgrades and brings a few improvements.

What’s New

Minor Improvements

• Connection pool metrics:
  • Add a psid label, populated if it is provided when connecting. This should be the case starting from the second connection to a synchronizer, or upon LSU.
  • Close the connection-health and subscription-health metrics associated to the psid when the pool is closed, instead of closing all the existing ones when the pool is started.
• Updated com.google.protobuf libs from 3.25.5 --> 3.25.9
• LSU: A call to AcknowledgeSigned with a timestamp before the upgrade time returns immediately, without any acknowledgement being done.
• Fix JDBC query for computing last activations: Under adverse conditions (data corruption) this query might called with empty inputs where it would have failed execution with PostgreSQL server version 14.
• (Potentially) BREAKING: Aggregatable submissions are now rejected eagerly to preserve bandwidth.
  This means that the submission error code SEQUENCER_AGGREGATE_SUBMISSION_ALREADY_SENT may now also
  be returned during the synchronous submission of the sequencer, as the state of the aggregation is also
  checked before ordering. In addition, the gRPC error code has been modified from FAILED_PRECONDITION to
  ALREADY_EXISTS to better reflect the nature of the error. Clients should be updated to handle this error
  code accordingly. Due to backwards compatibility, the old gRPC error code will be returned for PV35 and
  before on the async path, and the new capability must only be turned on when all nodes have been
  upgraded to a Canton version that supports this change. The new capability can be enabled using canton.sequencers.seq.parameters.enable-reject-delivered-aggregations-on-pv-35 = MED
  for mediators. This can be combined with the new configuration option of the mediator canton.mediators.mymediator.parameters.delayed-verdict-sender.enabled = true.
  Generally, the sequencer will send out the verdict after reaching the threshold. All subsequent sent verdicts are thrown away. The new option now allows threshold + extra verdicts to be sent immediately, while the rest of the mediators will wait a short amount of time. This allows to reduce the load on the sequencer by 30%, creating more capacity for other transactions.
• Fixed an issue that prevent external parties from being allocated on a participant with an offline root key via the Ledger API's PartyManagementService.AllocateExternalParty endpoint.
• Fixed an issue whereby the sequencer would no longer make progress after a failed write. Sequencers in such a state now report 'liveness' unhealthy.
• Require Participant Admin (not just IDP Admin) permissions in order to be able to grant CanReadAsAnyParty and CanExecuteAsAnyParty rights to users.

Bugfixes

(26-004, High): LSU: Missing synchronization between topology local copy and purging

Issue Description

Because of the lack of synchronization, it can happen that topology purging kicks in before the local copy of the topology state is finished, which result in incorrect topology state for the successor.

The issue can occur only when topology purging is enabled, which is not the case by default.

Affected Deployments

Participant nodes

Affected Versions

All versions before 3.5.6

Impact

Topology fork

Symptom

• Participant nodes issues warning/errors about missing topology transactions that were valid before the LSU.
• Submission of a transaction is rejected because of missing topology transactions that were valid before the LSU.

Workaround

Restore from backup and ensure topology purging is disabled

Likeliness

Exceptional

Recommendation

Upgrade to 3.5.6

Compatibility

The following Canton protocol versions are supported:

Dependency	Version
Canton protocol versions	34, 35

Canton has been tested against the following versions of its dependencies:

Dependency	Version
Java Runtime	OpenJDK 64-Bit Server VM (build 21.0.12+2-nixos, mixed mode, sharing)
Postgres	Recommended: PostgreSQL 17.10 (Debian 17.10-1.pgdg13+1) – Also tested: PostgreSQL 14.23 (Debian 14.23-1.pgdg13+1), PostgreSQL 15.18 (Debian 15.18-1.pgdg13+1), PostgreSQL 16.14 (Debian 16.14-1.pgdg13+1)