title_wip

#### New Feature[​](#new-feature-4 "Direct link to New Feature")

- Added a new `MergeTree` setting `deduplicate_merge_projection_mode` to control the projections during merges (for specific engines) and `OPTIMIZE DEDUPLICATE` query. Supported options: `throw` (throw an exception in case the projection is not fully supported for \*MergeTree engine), `drop` (remove projection during merge if it can't be merged itself consistently) and `rebuild` (rebuild projection from scratch, which is a heavy operation). [#66672](https://github.com/ClickHouse/ClickHouse/pull/66672) ([jsc0218](https://github.com/jsc0218)).
- Add `_etag` virtual column for S3 table engine. Fixes [#65312](https://github.com/ClickHouse/ClickHouse/issues/65312). [#65386](https://github.com/ClickHouse/ClickHouse/pull/65386) ([skyoct](https://github.com/skyoct)).
- Added a tagging (namespace) mechanism for the query cache. The same queries with different tags are considered different by the query cache. Example: `SELECT 1 SETTINGS use_query_cache = 1, query_cache_tag = 'abc'` and `SELECT 1 SETTINGS use_query_cache = 1, query_cache_tag = 'def'` now create different query cache entries. [#68235](https://github.com/ClickHouse/ClickHouse/pull/68235) ([sakulali](https://github.com/sakulali)).
- Support more variants of JOIN strictness (`LEFT/RIGHT SEMI/ANTI/ANY JOIN`) with inequality conditions which involve columns from both left and right table. e.g. `t1.y < t2.y` (see the setting `allow_experimental_join_condition`). [#64281](https://github.com/ClickHouse/ClickHouse/pull/64281) ([lgbo](https://github.com/lgbo-ustc)).
- Interpret Hive-style partitioning for different engines (`File`, `URL`, `S3`, `AzureBlobStorage`, `HDFS`). Hive-style partitioning organizes data into partitioned sub-directories, making it efficient to query and manage large datasets. Currently, it only creates virtual columns with the appropriate name and data. The follow-up PR will introduce the appropriate data filtering (performance speedup). [#65997](https://github.com/ClickHouse/ClickHouse/pull/65997) ([Yarik Briukhovetskyi](https://github.com/yariks5s)).
- Add function `printf` for Spark compatibility (but you can use the existing `format` function). [#66257](https://github.com/ClickHouse/ClickHouse/pull/66257) ([李扬](https://github.com/taiyang-li)).
- Add options `restore_replace_external_engines_to_null` and `restore_replace_external_table_functions_to_null` to replace external engines and table\_engines to `Null` engine that can be useful for testing. It should work for RESTORE and explicit table creation. [#66536](https://github.com/ClickHouse/ClickHouse/pull/66536) ([Ilya Yatsishin](https://github.com/qoega)).
- Added support for reading `MULTILINESTRING` geometry in `WKT` format using function `readWKTLineString`. [#67647](https://github.com/ClickHouse/ClickHouse/pull/67647) ([Jacob Reckhard](https://github.com/jacobrec)).
- Add a new table function `fuzzQuery`. This function allows the modification of a given query string with random variations. Example: `SELECT query FROM fuzzQuery('SELECT 1') LIMIT 5;`. [#67655](https://github.com/ClickHouse/ClickHouse/pull/67655) ([pufit](https://github.com/pufit)).
- Add a query `ALTER TABLE ... DROP DETACHED PARTITION ALL` to drop all detached partitions. [#67885](https://github.com/ClickHouse/ClickHouse/pull/67885) ([Duc Canh Le](https://github.com/canhld94)).
- Add the `rows_before_aggregation_at_least` statistic to the query response when a new setting, `rows_before_aggregation` is enabled. This statistic represents the number of rows read before aggregation. In the context of a distributed query, when using the `group by` or `max` aggregation function without a `limit`, `rows_before_aggregation_at_least` can reflect the number of rows hit by the query. [#66084](https://github.com/ClickHouse/ClickHouse/pull/66084) ([morning-color](https://github.com/morning-color)).
- Support `OPTIMIZE` query on `Join` tables to reduce their memory footprint. [#67883](https://github.com/ClickHouse/ClickHouse/pull/67883) ([Duc Canh Le](https://github.com/canhld94)).
- Allow run query instantly in play if you add `&run=1` in the URL [#66457](https://github.com/ClickHouse/ClickHouse/pull/66457) ([Aleksandr Musorin](https://github.com/AVMusorin)).

#### Experimental Feature[​](#experimental-feature-3 "Direct link to Experimental Feature")

- Implement a new `JSON` data type. [#66444](https://github.com/ClickHouse/ClickHouse/pull/66444) ([Kruglov Pavel](https://github.com/Avogar)).
- Add the new `TimeSeries` table engine. [#64183](https://github.com/ClickHouse/ClickHouse/pull/64183) ([Vitaly Baranov](https://github.com/vitlibar)).
- Add new experimental `Kafka` storage engine to store offsets in Keeper instead of relying on committing them to Kafka. It makes the commit to ClickHouse tables atomic with regard to consumption from the queue. [#57625](https://github.com/ClickHouse/ClickHouse/pull/57625) ([János Benjamin Antal](https://github.com/antaljanosbenjamin)).
- Use adaptive read task size calculation method (adaptive meaning it depends on read column sizes) for parallel replicas. [#60377](https://github.com/ClickHouse/ClickHouse/pull/60377) ([Nikita Taranov](https://github.com/nickitat)).
- Added statistics type `count_min` (count-min sketches) which provide selectivity estimations for equality predicates like `col = 'val'`. Supported data types are string, date, datatime and numeric types. [#65521](https://github.com/ClickHouse/ClickHouse/pull/65521) ([JackyWoo](https://github.com/JackyWoo)).

#### Performance Improvement[​](#performance-improvement-4 "Direct link to Performance Improvement")

- Setting `optimize_functions_to_subcolumns` is enabled by default. [#68053](https://github.com/ClickHouse/ClickHouse/pull/68053) ([Anton Popov](https://github.com/CurtizJ)).
- Store the `plain_rewritable` disk directory metadata in `__meta` layout, separately from the merge tree data in the object storage. Move the `plain_rewritable` disk to a flat directory structure. [#65751](https://github.com/ClickHouse/ClickHouse/pull/65751) ([Julia Kartseva](https://github.com/jkartseva)).
- Improve columns squashing (an operation happening in INSERT queries) for `String`/`Array`/`Map`/`Variant`/`Dynamic` types by reserving required memory in advance for all subcolumns. [#67043](https://github.com/ClickHouse/ClickHouse/pull/67043) ([Kruglov Pavel](https://github.com/Avogar)).
- Speed up `SYSTEM FLUSH LOGS` and flush logs on shutdown. [#67472](https://github.com/ClickHouse/ClickHouse/pull/67472) ([Sema Checherinda](https://github.com/CheSema)).
- Improved overall performance of merges by reducing the overhead of the scheduling steps of merges. [#68016](https://github.com/ClickHouse/ClickHouse/pull/68016) ([Anton Popov](https://github.com/CurtizJ)).
- Speed up tables removal for `DROP DATABASE` query, increased the default value for `database_catalog_drop_table_concurrency` to 16. [#67228](https://github.com/ClickHouse/ClickHouse/pull/67228) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Avoid allocating too much capacity for array column while writing ORC. Performance speeds up 15% for an Array column. [#67879](https://github.com/ClickHouse/ClickHouse/pull/67879) ([李扬](https://github.com/taiyang-li)).
- Speed up mutations for non-replicated MergeTree significantly [#66911](https://github.com/ClickHouse/ClickHouse/pull/66911) [#66909](https://github.com/ClickHouse/ClickHouse/pull/66909) ([Alexey Milovidov](https://github.com/alexey-milovidov)).

#### Improvement[​](#improvement-4 "Direct link to Improvement")