v26.2 Changelog for Cloud

### Insert and deduplication[​](#insert-and-deduplication "Direct link to Insert and deduplication")

- Async insert deduplication now works with dependent materialized views. When a `block_id` collision occurs, the original block is filtered to remove rows associated with the colliding `block_id`, and the remaining rows are transformed through all relevant materialized view queries. [#89140](https://github.com/ClickHouse/ClickHouse/pull/89140) ([Sema Checherinda](https://github.com/CheSema)).
- Async inserts now support parallel quorum — inserted data is replicated to the quorum, and if duplicates are found, the query waits until previously inserted data is replicated as well. [#93356](https://github.com/ClickHouse/ClickHouse/pull/93356) ([Sema Checherinda](https://github.com/CheSema)).
- Added `insert_deduplication_version` server setting to enable migration to a unified deduplication hash. [#95409](https://github.com/ClickHouse/ClickHouse/pull/95409) ([Sema Checherinda](https://github.com/CheSema)).
- Started migration of deduplication hashes. [#97562](https://github.com/ClickHouse/ClickHouse/pull/97562) ([Sema Checherinda](https://github.com/CheSema)).

### SQL and query features[​](#sql-and-query-features "Direct link to SQL and query features")

- Added `SYSTEM CLEAR [...] CACHE` syntax as a clearer alternative to the existing `SYSTEM DROP [...] CACHE`. The old syntax remains available. [#93727](https://github.com/ClickHouse/ClickHouse/pull/93727) ([Pranav Tiwari](https://github.com/pranavt84)).
- Added `OPTIMIZE <table> DRY RUN PARTS <part names>` query to simulate merges without committing the result part. Useful for verifying merge correctness, reproducing merge-related bugs, and benchmarking merge performance. [#96122](https://github.com/ClickHouse/ClickHouse/pull/96122) ([Anton Popov](https://github.com/CurtizJ)).
- DDL queries with `ON CLUSTER` can now be executed for Replicated databases when the `ignore_on_cluster_for_replicated_database` setting is enabled. The cluster name will be ignored. [#92872](https://github.com/ClickHouse/ClickHouse/pull/92872) ([Kirill](https://github.com/kirillgarbar)).
- Introduced a new syntax and framework to simplify and extend the projection index feature. [#91844](https://github.com/ClickHouse/ClickHouse/pull/91844) ([Amos Bird](https://github.com/amosbird)).

### Settings and configuration[​](#settings-and-configuration "Direct link to Settings and configuration")

- Added `max_insert_block_size_bytes` setting for finer control over the formation of inserted blocks. [#92833](https://github.com/ClickHouse/ClickHouse/pull/92833) ([Kirill Kopnev](https://github.com/Fgrtue)).
- Added `use_primary_key` setting. Set it to `false` to disable granule pruning based on the primary key. [#93319](https://github.com/ClickHouse/ClickHouse/pull/93319) ([Nihal Z. Miaji](https://github.com/nihalzp)).
- Added `default_dictionary_database` setting, which lets ClickHouse resolve external dictionaries referenced without a database qualifier in a specified default database. This simplifies migration from XML-defined global dictionaries to SQL-defined per-database dictionaries. [#91412](https://github.com/ClickHouse/ClickHouse/pull/91412) ([Dmitrii Plotnikov](https://github.com/dimbo4ka)).
- Added `check_named_collection_dependencies` setting (enabled by default) to prevent dropping named collections that are used by tables. [#96181](https://github.com/ClickHouse/ClickHouse/pull/96181) ([Pablo Marcos](https://github.com/pamarcos)).
- Added a max-min fair scheduler for concurrency control, providing better fairness under high oversubscription where many queries compete for limited CPU slots. The `concurrent_threads_scheduler` server setting now defaults to `max_min_fair` instead of `fair_round_robin`, so short-running queries are no longer penalized by long-running ones. [#94732](https://github.com/ClickHouse/ClickHouse/pull/94732) [#95300](https://github.com/ClickHouse/ClickHouse/pull/95300) ([Sergei Trifonov](https://github.com/serxa)).
- Added `logger.startup_console_level` and `logger.shutdown_console_level` configuration options to override the console log level during ClickHouse startup and shutdown respectively. [#95919](https://github.com/ClickHouse/ClickHouse/pull/95919) ([Garrett Thomas](https://github.com/garrettthomaskth)).

### Monitoring[​](#monitoring "Direct link to Monitoring")

- Added a `ClickHouse_Info` metric to the Prometheus `/metrics` endpoint containing version information, making it possible to build charts tracking detailed version information over time. [#91125](https://github.com/ClickHouse/ClickHouse/pull/91125) ([Christoph Wurm](https://github.com/cwurm)).

## Experimental Features[​](#experimental-features "Direct link to Experimental Features")

- Vector search can now distribute the load across replicas in a cluster, enabling support for large vector indexes that exceed the memory capacity of a single VM. [#95876](https://github.com/ClickHouse/ClickHouse/pull/95876) ([Shankar Iyer](https://github.com/shankar-iyer)).
- Added a server-side AST fuzzer controlled by the `ast_fuzzer_runs` and `ast_fuzzer_any_query` settings. When enabled, the server runs randomized mutations of each query after its normal execution, discarding the results. [#97568](https://github.com/ClickHouse/ClickHouse/pull/97568) ([Alexey Milovidov](https://github.com/alexey-milovidov)).

## Improvements[​](#improvements "Direct link to Improvements")

### Query and SQL[​](#query-and-sql-improvements "Direct link to Query and SQL")