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EmailClickHouse v25.4
Rapidly evolving OLAP database with experimental Iceberg read support, time travel, REST catalogs, and comprehensive write capabilities planned for 2025
Key Features
Evolving Catalog Support
Path (Hadoop-style) since 24.3, REST catalog (Nessie, Polaris/Unity, Glue REST) in 24.12; HMS experimental & AWS Glue in testing; R2 catalog on roadmap
Read-Only Analytics
ENGINE=Iceberg tables and icebergS3()/icebergCluster() functions; full SQL on Parquet files. Writes/compaction scheduled Q3 2025
No DML Operations
Reading of position & equality deletes supported since 24.12; queries merge delete files on-the-fly (MoR). No DELETE/UPDATE/MERGE writers until write support lands
Read-Only Storage Strategy
Copy-on-Write always readable; Merge-on-Read readable from 24.12 (non-materialized delete files)
No Streaming Support
No native streaming ingestion; users poll Iceberg or ingest with ClickHouse Kafka engine; roadmap includes ClickPipe Iceberg-CDC for near-real-time sync
No Format V3 Support
Not yet supported - engine rejects DV tables; v3 reader/writer planned post-spec-v2 completeness; DV/lineage scheduled Q3 2025
Time Travel Capabilities
Time-travel since 25.4 with SET iceberg_timestamp_ms=<epoch> or iceberg_snapshot_id; partition pruning via use_iceberg_partition_pruning=1
Basic Security Model
Relies on object-store credentials (AWS_ACCESS_KEY_ID, S3 V4 tokens) or catalog credential vending; ClickHouse RBAC controls database/table access; no column-masking yet
Experimental Engine Status
Engine still experimental; cold-start latency without distributed cache; complex joins benefit from data-shuffling behind stateless workers (prototype)
Comprehensive 2025 Roadmap
2025-H1: full spec-v2 compliance; Q3: Iceberg write path, native compaction, spec-v3 enablement; Performance: distributed cache, stateless workers
ClickHouse Iceberg Feature Matrix
Comprehensive breakdown of Iceberg capabilities in ClickHouse v25.4
Dimension | Support Level | Implementation Details | Since Version |
|---|---|---|---|
Catalog Types | PartialREST + Experimental | Path-based (24.3), REST catalog (24.12), HMS experimental, AWS Glue testing, R2 roadmap | 24.3+ |
SQL Analytics | PartialRead-Only | ENGINE=Iceberg, icebergS3(), icebergCluster() functions; full SQL reads; writes Q3 2025 | 24.3+ |
DML Operations | NoneDelete File Reading | Reads position/equality deletes (24.12), merges on-the-fly; no DELETE/UPDATE/MERGE writers | 24.12 |
Storage Strategy | PartialRead CoW + MoR | CoW always readable; MoR readable from 24.12 (non-materialized delete files) | 24.12 |
Streaming Support | LimitedPolling + Kafka | No native streaming; polling/Kafka engine patterns; ClickPipe Iceberg-CDC on roadmap | N/A |
Format Support | Nonev1/v2 Only | Reads spec v1/v2; engine rejects DV tables; v3 DV/lineage scheduled Q3 2025 | 24.3+ |
Time Travel | FullSince 25.4 | SET iceberg_timestamp_ms/iceberg_snapshot_id; partition pruning optimization | 25.4 |
Schema Evolution | FullRead Support | Reads evolved schemas; manifest/metadata cache (25.4); DESCRIBE shows latest schema | 24.8+ |
Security & Governance | PartialBasic RBAC | Object-store credentials, catalog vending, ClickHouse RBAC; no column-masking | 24.3+ |
Performance Features | PartialCache + Roadmap | Metadata cache (25.4); distributed cache & stateless workers roadmap (H2 2025) | 25.4 |
Engine Status | ExperimentalRapid Evolution | Experimental engine with rapid development; production readiness planned H2 2025 | 24.3+ |
2025 Roadmap | ComprehensiveDetailed Plan | H1: spec-v2 complete; Q3: write path, compaction, spec-v3; Performance optimizations | 2025 |
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For issues, click here (GitHub)Use Cases
High-Performance Analytics
OLAP queries on large-scale Iceberg data lakes
- Real-time dashboards on batch-updated data
- Complex analytical queries with sub-second latency
- Large-scale data warehouse analytics
- Time-series analysis and aggregation
Data Lake Query Layer
Fast analytical layer over multi-engine data lakes
- Analytics on data written by Spark/Flink
- Cross-catalog federated queries
- Historical analysis with time travel
- Performance layer for BI tools
Experimental Early Adoption
Testing cutting-edge Iceberg features and performance
- Prototype development with latest features
- Performance benchmarking and testing
- Early feedback on roadmap features
- Migration planning for future production use
Future Production Workloads
Planning for comprehensive read-write capabilities
- Teams planning 2025 migration to ClickHouse + Iceberg
- Organizations requiring roadmap-based commitments
- ETL pipelines with planned write capabilities
- Data architectures evolving with ClickHouse roadmap
Resources & Documentation
Official Documentation
Complete API reference and guides
Getting Started Guide
Quick start tutorials and examples
Iceberg Engine Documentation
Documentation
ClickHouse Release 25.04
Documentation
ClickHouse Release 24.12
Documentation
Iceberg Roadmap (GitHub)
Documentation
Distributed Cache Blog
Documentation
Open House Conference Highlights
Documentation
S3 Table Function Docs
Documentation
S3Queue Engine Docs
Documentation