2023 Changelog

### ClickHouse release 23.6, 2023-06-29. [Presentation](https://presentations.clickhouse.com/2023-release-23.6/), [Video](https://www.youtube.com/watch?v=cuf_hYn7dqU)[​](#236 "Direct link to 236")

#### Backward Incompatible Change[​](#backward-incompatible-change-6 "Direct link to Backward Incompatible Change")

- Delete feature `do_not_evict_index_and_mark_files` in the fs cache. This feature was only making things worse. [#51253](https://github.com/ClickHouse/ClickHouse/pull/51253) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Remove ALTER support for experimental LIVE VIEW. [#51287](https://github.com/ClickHouse/ClickHouse/pull/51287) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Decrease the default values for `http_max_field_value_size` and `http_max_field_name_size` to 128 KiB. [#51163](https://github.com/ClickHouse/ClickHouse/pull/51163) ([Mikhail f. Shiryaev](https://github.com/Felixoid)).
- CGroups metrics related to CPU are replaced with one metric, `CGroupMaxCPU` for better usability. The `Normalized` CPU usage metrics will be normalized to CGroups limits instead of the total number of CPUs when they are set. This closes [#50836](https://github.com/ClickHouse/ClickHouse/issues/50836). [#50835](https://github.com/ClickHouse/ClickHouse/pull/50835) ([Alexey Milovidov](https://github.com/alexey-milovidov)).

#### New Feature[​](#new-feature-6 "Direct link to New Feature")

- The function `transform` as well as `CASE` with value matching started to support all data types. This closes [#29730](https://github.com/ClickHouse/ClickHouse/issues/29730). This closes [#32387](https://github.com/ClickHouse/ClickHouse/issues/32387). This closes [#50827](https://github.com/ClickHouse/ClickHouse/issues/50827). This closes [#31336](https://github.com/ClickHouse/ClickHouse/issues/31336). This closes [#40493](https://github.com/ClickHouse/ClickHouse/issues/40493). [#51351](https://github.com/ClickHouse/ClickHouse/pull/51351) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Added option `--rename_files_after_processing <pattern>`. This closes [#34207](https://github.com/ClickHouse/ClickHouse/issues/34207). [#49626](https://github.com/ClickHouse/ClickHouse/pull/49626) ([alekseygolub](https://github.com/alekseygolub)).
- Add support for `TRUNCATE` modifier in `INTO OUTFILE` clause. Suggest using `APPEND` or `TRUNCATE` for `INTO OUTFILE` when file exists. [#50950](https://github.com/ClickHouse/ClickHouse/pull/50950) ([alekar](https://github.com/alekar)).
- Add table engine `Redis` and table function `redis`. It allows querying external Redis servers. [#50150](https://github.com/ClickHouse/ClickHouse/pull/50150) ([JackyWoo](https://github.com/JackyWoo)).
- Allow to skip empty files in file/s3/url/hdfs table functions using settings `s3_skip_empty_files`, `hdfs_skip_empty_files`, `engine_file_skip_empty_files`, `engine_url_skip_empty_files`. [#50364](https://github.com/ClickHouse/ClickHouse/pull/50364) ([Kruglov Pavel](https://github.com/Avogar)).
- Add a new setting named `use_mysql_types_in_show_columns` to alter the `SHOW COLUMNS` SQL statement to display MySQL equivalent types when a client is connected via the MySQL compatibility port. [#49577](https://github.com/ClickHouse/ClickHouse/pull/49577) ([Thomas Panetti](https://github.com/tpanetti)).
- Clickhouse-client can now be called with a connection string instead of "--host", "--port", "--user" etc. [#50689](https://github.com/ClickHouse/ClickHouse/pull/50689) ([Alexey Gerasimchuck](https://github.com/Demilivor)).
- Add setting `session_timezone`; it is used as the default timezone for a session when not explicitly specified. [#44149](https://github.com/ClickHouse/ClickHouse/pull/44149) ([Andrey Zvonov](https://github.com/zvonand)).
- Codec DEFLATE\_QPL is now controlled via server setting "enable\_deflate\_qpl\_codec" (default: false) instead of setting "allow\_experimental\_codecs". This marks DEFLATE\_QPL non-experimental. [#50775](https://github.com/ClickHouse/ClickHouse/pull/50775) ([Robert Schulze](https://github.com/rschu1ze)).

#### Performance Improvement[​](#performance-improvement-6 "Direct link to Performance Improvement")

- Improved scheduling of merge selecting and cleanup tasks in `ReplicatedMergeTree`. The tasks will not be executed too frequently when there's nothing to merge or cleanup. Added settings `max_merge_selecting_sleep_ms`, `merge_selecting_sleep_slowdown_factor`, `max_cleanup_delay_period` and `cleanup_thread_preferred_points_per_iteration`. It should close [#31919](https://github.com/ClickHouse/ClickHouse/issues/31919). [#50107](https://github.com/ClickHouse/ClickHouse/pull/50107) ([Alexander Tokmakov](https://github.com/tavplubix)).
- Make filter push down through cross join. [#50605](https://github.com/ClickHouse/ClickHouse/pull/50605) ([Han Fei](https://github.com/hanfei1991)).
- Improve performance with enabled QueryProfiler using thread-local timer\_id instead of global object. [#48778](https://github.com/ClickHouse/ClickHouse/pull/48778) ([Jiebin Sun](https://github.com/jiebinn)).
- Rewrite CapnProto input/output format to improve its performance. Map column names and CapnProto fields case insensitive, fix reading/writing of nested structure fields. [#49752](https://github.com/ClickHouse/ClickHouse/pull/49752) ([Kruglov Pavel](https://github.com/Avogar)).
- Optimize parquet write performance for parallel threads. [#50102](https://github.com/ClickHouse/ClickHouse/pull/50102) ([Hongbin Ma](https://github.com/binmahone)).
- Disable `parallelize_output_from_storages` for processing MATERIALIZED VIEWs and storages with one block only. [#50214](https://github.com/ClickHouse/ClickHouse/pull/50214) ([Azat Khuzhin](https://github.com/azat)).
- Merge PR [#46558](https://github.com/ClickHouse/ClickHouse/pull/46558). Avoid block permutation during sort if the block is already sorted. [#50697](https://github.com/ClickHouse/ClickHouse/pull/50697) ([Alexey Milovidov](https://github.com/alexey-milovidov), [Maksim Kita](https://github.com/kitaisreal)).
- Make multiple list requests to ZooKeeper in parallel to speed up reading from system.zookeeper table. [#51042](https://github.com/ClickHouse/ClickHouse/pull/51042) ([Alexander Gololobov](https://github.com/davenger)).
- Speedup initialization of DateTime lookup tables for time zones. This should reduce startup/connect time of clickhouse-client especially in debug build as it is rather heavy. [#51347](https://github.com/ClickHouse/ClickHouse/pull/51347) ([Alexander Gololobov](https://github.com/davenger)).
- Fix data lakes slowness because of synchronous head requests. (Related to Iceberg/Deltalake/Hudi being slow with a lot of files). [#50976](https://github.com/ClickHouse/ClickHouse/pull/50976) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Do not read all the columns from right GLOBAL JOIN table. [#50721](https://github.com/ClickHouse/ClickHouse/pull/50721) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).

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

- Support parallel replicas with the analyzer. [#50441](https://github.com/ClickHouse/ClickHouse/pull/50441) ([Raúl Marín](https://github.com/Algunenano)).
- Add random sleep before large merges/mutations execution to split load more evenly between replicas in case of zero-copy replication. [#51282](https://github.com/ClickHouse/ClickHouse/pull/51282) ([alesapin](https://github.com/alesapin)).
- Do not replicate `ALTER PARTITION` queries and mutations through `Replicated` database if it has only one shard and the underlying table is `ReplicatedMergeTree`. [#51049](https://github.com/ClickHouse/ClickHouse/pull/51049) ([Alexander Tokmakov](https://github.com/tavplubix)).

#### Improvement[​](#improvement-6 "Direct link to Improvement")