Announcement: Addressing Assertion Errors and Quorum Failures in Cassandra 5.x Versions

At NetApp Instaclustr, we’re committed to helping our customers run stable and performant Cassandra clusters. As part of that commitment, we want to share an important update regarding Apache Cassandra 5 versions prior to version 5.0.6.

Issue Summary

In October 2025, Apache Cassandra Community reported an issue that has been affecting all versions of Cassandra 5 and is resolved in Cassandra 5.0.6. This issue can cause AssertionErrors during token-range read queries on tables using the BTI SSTable format, particularly when compaction and early-open operations overlap. When this occurs, read requests may fail with ReadFailureException at consistency levels such as QUORUM or LOCAL_QUORUM.

Issue Details

Symptom Impact Resolution
AssertionError in MmappedRegions during token-range queries on BTI SSTables Read failures, client-side quorum errors, intermittent query retries. Issue resolved in Cassandra 5.0.6. See https://issues.apache.org/jira/browse/CASSANDRA-20976

Issue Analysis

Clusters affected by this issue exhibit:

  • Non-deterministic read failures during range scans.
  • AssertionError logs referencing MmappedRegions and PartitionIndex.
  • Increased likelihood of getting affected with this bug during heavy read/write workloads and compaction.

Mitigation

The issue is resolved in Apache Cassandra 5.0.6. Cassandra 5.0.6 also includes additional stability improvements. See the full release notes here: https://github.com/apache/cassandra/blob/cassandra-5.0.6/CHANGES.txt

Managed Platform Customers:

Apache Cassandra 5.0.6 is now available on our platform for provisioning new clutsers, and upgrading your existing clusters.

Next steps:

  • All clusters currently running Cassandra 5.0.3 or 5.0.5 will be upgraded to 5.0.6.
    Note: Cassandra 5.0.4 was never released on the NetApp Instaclustr managed platform due to a performance regression in that version.
  • Customers will receive a scheduled maintenance notification prior to their upgrade.
  • No action is required from your side. Applications running on Cassandra 5.0.3 or 5.0.5 will be fully compatible with Cassandra 5.0.6. 

Enterprise support customers:

Please upgrade your clusters running on Cassandra 5.0.5 or prior to Cassandra 5.0.6 or a later version to avoid potential read failures.

Lifecycle Status

Guidance for our managed service and enterprise Support customers:

Please use Cassandra 5.0.6 or later for all new deployments as soon as is practical.

 

If you have any further queries regarding this, please contact Instaclustr Support.