2023 Changelog

#### New Feature[​](#new-feature-3 "Direct link to New Feature")

- Improve schema inference from JSON formats: 1) Now it's possible to infer named Tuples from JSON objects without experimental JSON type under a setting `input_format_json_try_infer_named_tuples_from_objects` in JSON formats. Previously without experimental type JSON we could only infer JSON objects as Strings or Maps, now we can infer named Tuple. Resulting Tuple type will conain all keys of objects that were read in data sample during schema inference. It can be useful for reading structured JSON data without sparse objects. The setting is enabled by default. 2) Allow parsing JSON array into a column with type String under setting `input_format_json_read_arrays_as_strings`. It can help reading arrays with values with different types. 3) Allow to use type String for JSON keys with unkown types (`null`/`[]`/`{}`) in sample data under setting `input_format_json_infer_incomplete_types_as_strings`. Now in JSON formats we can read any value into String column and we can avoid getting error `Cannot determine type for column 'column_name' by first 25000 rows of data, most likely this column contains only Nulls or empty Arrays/Maps` during schema inference by using type String for unknown types, so the data will be read successfully. [#54427](https://github.com/ClickHouse/ClickHouse/pull/54427) ([Kruglov Pavel](https://github.com/Avogar)).
- Added IO scheduling support for remote disks. Storage configuration for disk types `s3`, `s3_plain`, `hdfs` and `azure_blob_storage` can now contain `read_resource` and `write_resource` elements holding resource names. Scheduling policies for these resources can be configured in a separate server configuration section `resources`. Queries can be marked using setting `workload` and classified using server configuration section `workload_classifiers` to achieve diverse resource scheduling goals. More details in [the docs](/docs/operations/workload-scheduling). [#47009](https://github.com/ClickHouse/ClickHouse/pull/47009) ([Sergei Trifonov](https://github.com/serxa)). Added "bandwidth\_limit" IO scheduling node type. It allows you to specify `max_speed` and `max_burst` constraints on traffic passing though this node. [#54618](https://github.com/ClickHouse/ClickHouse/pull/54618) ([Sergei Trifonov](https://github.com/serxa)).
- Added new type of authentication based on SSH keys. It works only for the native TCP protocol. [#41109](https://github.com/ClickHouse/ClickHouse/pull/41109) ([George Gamezardashvili](https://github.com/InfJoker)).
- Added a new column `_block_number` for MergeTree tables. [#44532](https://github.com/ClickHouse/ClickHouse/issues/44532). [#47532](https://github.com/ClickHouse/ClickHouse/pull/47532) ([SmitaRKulkarni](https://github.com/SmitaRKulkarni)).
- Add `IF EMPTY` clause for `DROP TABLE` queries. [#48915](https://github.com/ClickHouse/ClickHouse/pull/48915) ([Pavel Novitskiy](https://github.com/pnovitskiy)).
- SQL functions `toString(datetime, timezone)` and `formatDateTime(datetime, format, timezone)` now support non-constant timezone arguments. [#53680](https://github.com/ClickHouse/ClickHouse/pull/53680) ([Yarik Briukhovetskyi](https://github.com/yariks5s)).
- Add support for `ALTER TABLE MODIFY COMMENT`. Note: something similar was added by an external contributor a long time ago, but the feature did not work at all and only confused users. This closes [#36377](https://github.com/ClickHouse/ClickHouse/issues/36377). [#51304](https://github.com/ClickHouse/ClickHouse/pull/51304) ([Alexey Milovidov](https://github.com/alexey-milovidov)). Note: this command does not propagate between replicas, so the replicas of a table could have different comments.
- Added `GCD` a.k.a. "greatest common denominator" as a new data compression codec. The codec computes the GCD of all column values, and then divides each value by the GCD. The GCD codec is a data preparation codec (similar to Delta and DoubleDelta) and cannot be used stand-alone. It works with data integer, decimal and date/time type. A viable use case for the GCD codec are column values that change (increase/decrease) in multiples of the GCD, e.g. 24 - 28 - 16 - 24 - 8 - 24 (assuming GCD = 4). [#53149](https://github.com/ClickHouse/ClickHouse/pull/53149) ([Alexander Nam](https://github.com/seshWCS)).
- Two new type aliases `DECIMAL(P)` (as shortcut for `DECIMAL(P, 0)` and `DECIMAL` (as shortcut for `DECIMAL(10, 0)`) were added. This makes ClickHouse more compatible with MySQL's SQL dialect. [#53328](https://github.com/ClickHouse/ClickHouse/pull/53328) ([Val Doroshchuk](https://github.com/valbok)).
- Added a new system log table `backup_log` to track all `BACKUP` and `RESTORE` operations. [#53638](https://github.com/ClickHouse/ClickHouse/pull/53638) ([Victor Krasnov](https://github.com/sirvickr)).
- Added a format setting `output_format_markdown_escape_special_characters` (default: false). The setting controls whether special characters like `!`, `#`, `$` etc. are escaped (i.e. prefixed by a backslash) in the `Markdown` output format. [#53860](https://github.com/ClickHouse/ClickHouse/pull/53860) ([irenjj](https://github.com/irenjj)).
- Add function `decodeHTMLComponent`. [#54097](https://github.com/ClickHouse/ClickHouse/pull/54097) ([Bharat Nallan](https://github.com/bharatnc)).
- Added `peak_threads_usage` to query\_log table. [#54335](https://github.com/ClickHouse/ClickHouse/pull/54335) ([Alexey Gerasimchuck](https://github.com/Demilivor)).
- Add `SHOW FUNCTIONS` support to clickhouse-client. [#54337](https://github.com/ClickHouse/ClickHouse/pull/54337) ([Julia Kartseva](https://github.com/wat-ze-hex)).
- Added function `toDaysSinceYearZero` with alias `TO_DAYS` (for compatibility with MySQL) which returns the number of days passed since `0001-01-01` (in Proleptic Gregorian Calendar). [#54479](https://github.com/ClickHouse/ClickHouse/pull/54479) ([Robert Schulze](https://github.com/rschu1ze)). Function `toDaysSinceYearZero` now supports arguments of type `DateTime` and `DateTime64`. [#54856](https://github.com/ClickHouse/ClickHouse/pull/54856) ([Serge Klochkov](https://github.com/slvrtrn)).
- Added functions `YYYYMMDDtoDate`, `YYYYMMDDtoDate32`, `YYYYMMDDhhmmssToDateTime` and `YYYYMMDDhhmmssToDateTime64`. They convert a date or date with time encoded as integer (e.g. 20230911) into a native date or date with time. As such, they provide the opposite functionality of existing functions `YYYYMMDDToDate`, `YYYYMMDDToDateTime`, `YYYYMMDDhhmmddToDateTime`, `YYYYMMDDhhmmddToDateTime64`. [#54509](https://github.com/ClickHouse/ClickHouse/pull/54509) ([Quanfa Fu](https://github.com/dentiscalprum)) ([Robert Schulze](https://github.com/rschu1ze)).
- Add several string distance functions, including `byteHammingDistance`, `editDistance`. [#54935](https://github.com/ClickHouse/ClickHouse/pull/54935) ([flynn](https://github.com/ucasfl)).
- Allow specifying the expiration date and, optionally, the time for user credentials with `VALID UNTIL datetime` clause. [#51261](https://github.com/ClickHouse/ClickHouse/pull/51261) ([Nikolay Degterinsky](https://github.com/evillique)).
- Allow S3-style URLs for table functions `s3`, `gcs`, `oss`. URL is automatically converted to HTTP. Example: `'s3://clickhouse-public-datasets/hits.csv'` is converted to `'https://clickhouse-public-datasets.s3.amazonaws.com/hits.csv'`. [#54931](https://github.com/ClickHouse/ClickHouse/pull/54931) ([Yarik Briukhovetskyi](https://github.com/yariks5s)).
- Add new setting `print_pretty_type_names` to print pretty deep nested types like Tuple/Maps/Arrays. [#55095](https://github.com/ClickHouse/ClickHouse/pull/55095) ([Kruglov Pavel](https://github.com/Avogar)).

#### Performance Improvement[​](#performance-improvement-3 "Direct link to Performance Improvement")