What’s New in Apache Cassandra 6.0

Preview | Unofficial | For review only

Apache Cassandra 6.0 introduces general-purpose ACID transactions, a new consensus-based cluster metadata system, and dozens of operational, CQL, and security improvements.

Headline Features

Accord (General-Purpose Transactions)

Cassandra 6.0 introduces Accord (CEP-15), a leaderless consensus protocol enabling multi-partition, multi-table ACID transactions. New CQL syntax BEGIN TRANSACTION … COMMIT TRANSACTION supports atomic reads and writes across partition boundaries. Accord transparently replaces Paxos for lightweight transactions (LWT/CAS) on migrated tables.

Transactional Cluster Metadata (TCM)

CEP-21 (CASSANDRA-18330) replaces gossip-based cluster metadata propagation with a linearized, distributed log managed by a Cluster Metadata Service (CMS). All modifications to cluster membership, token ownership, and schema are serialized through the CMS using Paxos-backed consensus. This is the largest architectural change in Cassandra 6.0.

CQL Enhancements

Constraints: CEP-42 (CASSANDRA-19947) adds a pluggable constraints framework. Supported constraint types include NOT NULL, scalar range checks, LENGTH, OCTET_LENGTH, REGEXP, and JSON. Constraints can be applied via CREATE TABLE, ALTER TABLE, CREATE CONSTRAINT, and ALTER CONSTRAINT.

Constraints Reference
BETWEEN Operator: CASSANDRA-19604 adds BETWEEN support in WHERE clauses for SAI-indexed columns and clustering columns. Syntax: WHERE col BETWEEN val1 AND val2.

Data Manipulation Reference
NOT Operators: CASSANDRA-18584 adds NOT IN, NOT CONTAINS, and NOT CONTAINS KEY operators for WHERE clauses, enabling exclusion-based filtering with SAI indexes.

Data Manipulation Reference
LIKE Expressions: CASSANDRA-17198 adds LIKE operator support in WHERE clauses for SASI and SAI indexes with prefix, suffix, and contains matching.

Data Manipulation Reference
CREATE TABLE LIKE: CASSANDRA-19964 adds the ability to create a new table with the same schema as an existing table.

Data Definition Reference
Schema Annotations (COMMENT ON / SECURITY LABEL): CASSANDRA-20943 adds COMMENT ON and SECURITY LABEL statements for annotating keyspaces, tables, columns, and other schema objects.

Data Definition Reference
LIST SUPERUSERS: CASSANDRA-19417 adds a new CQL statement to list all roles with superuser privileges.

CQL Security Reference
New String and Formatting Functions: length(), octet_length() (CASSANDRA-20102), format_bytes(), format_time() (CASSANDRA-19546) provide human-readable output formatting.

Functions Reference
SAI Frozen Collection Indexing: CASSANDRA-18492 enables SAI indexes on frozen collections, supporting CONTAINS queries on frozen lists, sets, and maps.

SAI Collections Indexing
Index Hints: CASSANDRA-18112 allows manual secondary index selection in CQL SELECT statements.

Data Manipulation Reference

Operational Changes

Topology and Snitches

Snitch Deprecation: CASSANDRA-19488 deprecates IEndpointSnitch in favor of new initial_location_provider, node_proximity, addresses_config, and prefer_local_connections settings in cassandra.yaml. Cloud-specific snitches (GoogleCloudSnitch, Ec2Snitch, AzureSnitch) are removed.

Snitches and Topology
Live DC/Rack Changes: CASSANDRA-20528 adds nodetool altertopology to change a live node’s datacenter or rack assignment without restart.

Security

JMX in cassandra.yaml: CASSANDRA-11695 moves JMX server configuration from cassandra-env.sh scripts to structured cassandra.yaml settings.

Security Overview
native_transport_port_ssl Removed: CASSANDRA-19397 removes the deprecated native_transport_port_ssl setting. Use native_transport_port with client_encryption_options instead.
Password Validation: CEP-24 (CASSANDRA-17457) adds pluggable password validation with dictionary checks, length requirements, and generated passwords.

Password Validation
Role Name Generation: CEP-55 adds UUID-based role name generation with configurable prefixes and suffixes.

Role Name Generation
Periodic Disconnect of Revoked Roles: CASSANDRA-19385 adds background task to disconnect clients whose roles have been revoked or set to LOGIN = false.

Compaction and Compression

ZSTD Dictionary Compression: CASSANDRA-17021 adds ZstdDictionaryCompressor with nodetool-managed dictionary training.

Compression
Compaction Parallelization: CASSANDRA-18802 adds parallelize_output_shards option for UCS and compaction --jobs parallelism.

Unified Compaction Strategy
Direct I/O for Compaction Reads: CASSANDRA-19987 adds compaction_read_disk_access_mode setting for O_DIRECT bypass of OS page cache during compaction.

Repair and Recovery

Auto Repair: CEP-37 (CASSANDRA-19918) adds automated, adaptive repair scheduling with configurable splitter algorithms and per-table policies.

Automated Repair

Monitoring and Observability

Slow Query Virtual Table: CASSANDRA-13001 adds system_views.slow_queries for CQL-queryable slow query logging.
system_metrics Virtual Keyspace: CASSANDRA-14572 exposes all Dropwizard metrics as CQL-queryable virtual tables in the system_metrics keyspace.
uncaught_exceptions Virtual Table: CASSANDRA-20858 adds system_views.uncaught_exceptions tracking thread exceptions.
Partition Key Statistics: CASSANDRA-20161 adds system_views.partition_key_statistics exposing per-table partition size estimates.

Virtual Tables

Guardrails

Cassandra 6.0 adds several new guardrails for operational safety:

Bulk loading guardrail (CASSANDRA-18781) — control sstableloader and bulk import permissions
Keyspace DDL guardrails (CASSANDRA-20913) — protect against accidental ALTER/DROP of keyspace properties
Disk usage guardrails (CASSANDRA-21024) — strategy-aware disk usage protection per datacenter
Per-type max size (CASSANDRA-19677) — configurable size limits for collections, UDTs, and other types

Guardrails Reference

Tools

Custom Startup Checks (SPI): CASSANDRA-21093 adds a pluggable SPI for custom pre-startup validation checks.

Custom Startup Checks
Async Profiler Integration: CASSANDRA-20854 adds nodetool profile subcommands for CPU, allocation, and lock profiling.

Async Profiler

Configuration

JDK 21 and Generational ZGC: CASSANDRA-18831 adds JDK 21 support with Generational ZGC as the default garbage collector. New jvm21-server.options file.
Environment Variable Overrides: CASSANDRA-20749 allows cassandra.yaml settings to be overridden via environment variables.
TriggersPolicy: CASSANDRA-19532 adds triggers_policy setting (enabled/disabled/forbidden) to control trigger usage at the cluster level.

Breaking Changes and Deprecations

native_transport_port_ssl has been removed (CASSANDRA-19397)
Cloud-specific snitches removed; use initial_location_provider settings instead (CASSANDRA-19488)
IEndpointSnitch interface deprecated; replaced by new location/proximity interfaces
Sigar replaced by OSHI for hardware detection (CASSANDRA-16565)
JDK 17 is the minimum supported version; JDK 11 is no longer supported
use_deterministic_table_id deprecated and removed from default cassandra.yaml (CASSANDRA-19809)

Previous Releases

For features introduced in earlier releases, see:

What’s New in Cassandra 5.0