2021 Changelog

- New asynchronous INSERT mode allows to accumulate inserted data and store it in a single batch in background. On client it can be enabled by setting `async_insert` for `INSERT` queries with data inlined in query or in separate buffer (e.g. for `INSERT` queries via HTTP protocol). If `wait_for_async_insert` is true (by default) the client will wait until data will be flushed to table. On server-side it controlled by the settings `async_insert_threads`, `async_insert_max_data_size` and `async_insert_busy_timeout_ms`. Implements [#18282](https://github.com/ClickHouse/ClickHouse/issues/18282). [#27537](https://github.com/ClickHouse/ClickHouse/pull/27537) ([Anton Popov](https://github.com/CurtizJ)). [#20557](https://github.com/ClickHouse/ClickHouse/pull/20557) ([Ivan](https://github.com/abyss7)). Notes on performance: with asynchronous inserts you can do up to around 10 000 individual INSERT queries per second, so it is still recommended to insert in batches if you want to achieve performance up to millions inserted rows per second.
- Add interactive mode for `clickhouse-local`. So, you can just run `clickhouse-local` to get a command line ClickHouse interface without connecting to a server and process data from files and external data sources. Also merge the code of `clickhouse-client` and `clickhouse-local` together. Closes [#7203](https://github.com/ClickHouse/ClickHouse/issues/7203). Closes [#25516](https://github.com/ClickHouse/ClickHouse/issues/25516). Closes [#22401](https://github.com/ClickHouse/ClickHouse/issues/22401). [#26231](https://github.com/ClickHouse/ClickHouse/pull/26231) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Added support for executable (scriptable) user defined functions. These are UDFs that can be written in any programming language. [#28803](https://github.com/ClickHouse/ClickHouse/pull/28803) ([Maksim Kita](https://github.com/kitaisreal)).
- Allow predefined connections to external data sources. This allows to avoid specifying credentials or addresses while using external data sources, they can be referenced by names instead. Closes [#28367](https://github.com/ClickHouse/ClickHouse/issues/28367). [#28577](https://github.com/ClickHouse/ClickHouse/pull/28577) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Added `INFORMATION_SCHEMA` database with `SCHEMATA`, `TABLES`, `VIEWS` and `COLUMNS` views to the corresponding tables in `system` database. Closes [#9770](https://github.com/ClickHouse/ClickHouse/issues/9770). [#28691](https://github.com/ClickHouse/ClickHouse/pull/28691) ([tavplubix](https://github.com/tavplubix)).
- Support `EXISTS (subquery)`. Closes [#6852](https://github.com/ClickHouse/ClickHouse/issues/6852). [#29731](https://github.com/ClickHouse/ClickHouse/pull/29731) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Session logging for audit. Logging all successful and failed login and logout events to a new `system.session_log` table. [#22415](https://github.com/ClickHouse/ClickHouse/pull/22415) ([Vasily Nemkov](https://github.com/Enmk)) ([Vitaly Baranov](https://github.com/vitlibar)).
- Support multidimensional cosine distance and euclidean distance functions; L1, L2, Lp, Linf distances and norms. Scalar product on tuples and various arithmetic operators on tuples. This fully closes [#4509](https://github.com/ClickHouse/ClickHouse/issues/4509) and even more. [#27933](https://github.com/ClickHouse/ClickHouse/pull/27933) ([Alexey Boykov](https://github.com/mathalex)).
- Add support for compression and decompression for `INTO OUTFILE` and `FROM INFILE` (with autodetect or with additional optional parameter). [#27135](https://github.com/ClickHouse/ClickHouse/pull/27135) ([Filatenkov Artur](https://github.com/FArthur-cmd)).
- Add CORS (Cross Origin Resource Sharing) support with HTTP `OPTIONS` request. It means, now Grafana will work with serverless requests without a kludges. Closes [#18693](https://github.com/ClickHouse/ClickHouse/issues/18693). [#29155](https://github.com/ClickHouse/ClickHouse/pull/29155) ([Filatenkov Artur](https://github.com/FArthur-cmd)).
- Queries with JOIN ON now supports disjunctions (OR). [#21320](https://github.com/ClickHouse/ClickHouse/pull/21320) ([Ilya Golshtein](https://github.com/ilejn)).
- Added function `tokens`. That allow to split string into tokens using non-alpha numeric ASCII characters as separators. [#29981](https://github.com/ClickHouse/ClickHouse/pull/29981) ([Maksim Kita](https://github.com/kitaisreal)). Added function `ngrams` to extract ngrams from text. Closes [#29699](https://github.com/ClickHouse/ClickHouse/issues/29699). [#29738](https://github.com/ClickHouse/ClickHouse/pull/29738) ([Maksim Kita](https://github.com/kitaisreal)).
- Add functions for Unicode normalization: `normalizeUTF8NFC`, `normalizeUTF8NFD`, `normalizeUTF8NFKC`, `normalizeUTF8NFKD` functions. [#28633](https://github.com/ClickHouse/ClickHouse/pull/28633) ([darkkeks](https://github.com/darkkeks)).
- Streaming consumption of application log files in ClickHouse with `FileLog` table engine. It's like `Kafka` or `RabbitMQ` engine but for append-only and rotated logs in local filesystem. Closes [#6953](https://github.com/ClickHouse/ClickHouse/issues/6953). [#25969](https://github.com/ClickHouse/ClickHouse/pull/25969) ([flynn](https://github.com/ucasfl)) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add `CapnProto` output format, refactor `CapnProto` input format. [#29291](https://github.com/ClickHouse/ClickHouse/pull/29291) ([Kruglov Pavel](https://github.com/Avogar)).
- Allow to write number in query as binary literal. Example `SELECT 0b001;`. [#29304](https://github.com/ClickHouse/ClickHouse/pull/29304) ([Maksim Kita](https://github.com/kitaisreal)).
- Added `hashed_array` dictionary type. It saves memory when using dictionaries with multiple attributes. Closes [#30236](https://github.com/ClickHouse/ClickHouse/issues/30236). [#30242](https://github.com/ClickHouse/ClickHouse/pull/30242) ([Maksim Kita](https://github.com/kitaisreal)).
- Added `JSONExtractKeys` function. [#30056](https://github.com/ClickHouse/ClickHouse/pull/30056) ([Vitaly](https://github.com/orloffv)).
- Add a function `getOSKernelVersion` - it returns a string with OS kernel version. [#29755](https://github.com/ClickHouse/ClickHouse/pull/29755) ([Memo](https://github.com/Joeywzr)).
- Added `MD4` and `SHA384` functions. MD4 is an obsolete and insecure hash function, it can be used only in rare cases when MD4 is already being used in some legacy system and you need to get exactly the same result. [#29602](https://github.com/ClickHouse/ClickHouse/pull/29602) ([Nikita Tikhomirov](https://github.com/NSTikhomirov)).
- HSTS can be enabled for ClickHouse HTTP server by setting `hsts_max_age` in configuration file with a positive number. [#29516](https://github.com/ClickHouse/ClickHouse/pull/29516) ([凌涛](https://github.com/lingtaolf)).
- Huawei OBS Storage support. Closes [#24294](https://github.com/ClickHouse/ClickHouse/issues/24294). [#29511](https://github.com/ClickHouse/ClickHouse/pull/29511) ([kevin wan](https://github.com/MaxWk)).
- New function `mapContainsKeyLike` to get the map that key matches a simple regular expression. [#29471](https://github.com/ClickHouse/ClickHouse/pull/29471) ([凌涛](https://github.com/lingtaolf)). New function `mapExtractKeyLike` to get the map only kept elements matched specified pattern. [#30793](https://github.com/ClickHouse/ClickHouse/pull/30793) ([凌涛](https://github.com/lingtaolf)).
- Implemented `ALTER TABLE x MODIFY COMMENT`. [#29264](https://github.com/ClickHouse/ClickHouse/pull/29264) ([Vasily Nemkov](https://github.com/Enmk)).
- Adds H3 inspection functions that are missing from ClickHouse but are available via the H3 api: <https://h3geo.org/docs/api/inspection>. [#29209](https://github.com/ClickHouse/ClickHouse/pull/29209) ([Bharat Nallan](https://github.com/bharatnc)).
- Allow non-replicated ALTER TABLE FETCH and ATTACH in Replicated databases. [#29202](https://github.com/ClickHouse/ClickHouse/pull/29202) ([Kevin Michel](https://github.com/kmichel-aiven)).