2020 Changelog

#### Improvement[​](#improvement-14 "Direct link to Improvement")

- Allowed to set `JOIN` kind and type in more standard way: `LEFT SEMI JOIN` instead of `SEMI LEFT JOIN`. For now both are correct. [#12520](https://github.com/ClickHouse/ClickHouse/pull/12520) ([Artem Zuikov](https://github.com/4ertus2)).
- lifetime\_rows/lifetime\_bytes for Buffer engine. [#12421](https://github.com/ClickHouse/ClickHouse/pull/12421) ([Azat Khuzhin](https://github.com/azat)).
- Write the detail exception message to the client instead of 'MySQL server has gone away'. [#12383](https://github.com/ClickHouse/ClickHouse/pull/12383) ([BohuTANG](https://github.com/BohuTANG)).
- Allows to change a charset which is used for printing grids borders. Available charsets are following: UTF-8, ASCII. Setting `output_format_pretty_grid_charset` enables this feature. [#12372](https://github.com/ClickHouse/ClickHouse/pull/12372) ([Sabyanin Maxim](https://github.com/s-mx)).
- Supported MySQL 'SELECT DATABASE()' [#9336](https://github.com/ClickHouse/ClickHouse/issues/9336) 2. Add MySQL replacement query integration test. [#12314](https://github.com/ClickHouse/ClickHouse/pull/12314) ([BohuTANG](https://github.com/BohuTANG)).
- Added `KILL QUERY [connection_id]` for the MySQL client/driver to cancel the long query, issue [#12038](https://github.com/ClickHouse/ClickHouse/issues/12038). [#12152](https://github.com/ClickHouse/ClickHouse/pull/12152) ([BohuTANG](https://github.com/BohuTANG)).
- Added support for `%g` (two digit ISO year) and `%G` (four digit ISO year) substitutions in `formatDateTime` function. [#12136](https://github.com/ClickHouse/ClickHouse/pull/12136) ([vivarum](https://github.com/vivarum)).
- Added 'type' column in system.disks. [#12115](https://github.com/ClickHouse/ClickHouse/pull/12115) ([ianton-ru](https://github.com/ianton-ru)).
- Improved `REVOKE` command: now it requires grant/admin option for only access which will be revoked. For example, to execute `REVOKE ALL ON *.* FROM user1` now it does not require to have full access rights granted with grant option. Added command `REVOKE ALL FROM user1` - it revokes all granted roles from `user1`. [#12083](https://github.com/ClickHouse/ClickHouse/pull/12083) ([Vitaly Baranov](https://github.com/vitlibar)).
- Added replica priority for load\_balancing (for manual prioritization of the load balancing). [#11995](https://github.com/ClickHouse/ClickHouse/pull/11995) ([Azat Khuzhin](https://github.com/azat)).
- Switched paths in S3 metadata to relative which allows to handle S3 blobs more easily. [#11892](https://github.com/ClickHouse/ClickHouse/pull/11892) ([Vladimir Chebotarev](https://github.com/excitoon)).

#### Performance Improvement[​](#performance-improvement-7 "Direct link to Performance Improvement")

- Improved performace of 'ORDER BY' and 'GROUP BY' by prefix of sorting key (enabled with `optimize_aggregation_in_order` setting, disabled by default). [#11696](https://github.com/ClickHouse/ClickHouse/pull/11696) ([Anton Popov](https://github.com/CurtizJ)).
- Removed injective functions inside `uniq*()` if `set optimize_injective_functions_inside_uniq=1`. [#12337](https://github.com/ClickHouse/ClickHouse/pull/12337) ([Ruslan Kamalov](https://github.com/kamalov-ruslan)).
- Index not used for IN operator with literals, performance regression introduced around v19.3. This fixes [#10574](https://github.com/ClickHouse/ClickHouse/issues/10574). [#12062](https://github.com/ClickHouse/ClickHouse/pull/12062) ([nvartolomei](https://github.com/nvartolomei)).
- Implemented single part uploads for DiskS3 (experimental feature). [#12026](https://github.com/ClickHouse/ClickHouse/pull/12026) ([Vladimir Chebotarev](https://github.com/excitoon)).

#### Experimental Feature[​](#experimental-feature-4 "Direct link to Experimental Feature")

- Added new in-memory format of parts in `MergeTree`-family tables, which stores data in memory. Parts are written on disk at first merge. Part will be created in in-memory format if its size in rows or bytes is below thresholds `min_rows_for_compact_part` and `min_bytes_for_compact_part`. Also optional support of Write-Ahead-Log is available, which is enabled by default and is controlled by setting `in_memory_parts_enable_wal`. [#10697](https://github.com/ClickHouse/ClickHouse/pull/10697) ([Anton Popov](https://github.com/CurtizJ)).

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement-9 "Direct link to Build/Testing/Packaging Improvement")

- Implement AST-based query fuzzing mode for clickhouse-client. See [this label](https://github.com/ClickHouse/ClickHouse/issues?q=label%3Afuzz+is%3Aissue) for the list of issues we recently found by fuzzing. Most of them were found by this tool, and a couple by SQLancer and `00746_sql_fuzzy.pl`. [#12111](https://github.com/ClickHouse/ClickHouse/pull/12111) ([Alexander Kuzmenkov](https://github.com/akuzm)).
- Add new type of tests based on Testflows framework. [#12090](https://github.com/ClickHouse/ClickHouse/pull/12090) ([vzakaznikov](https://github.com/vzakaznikov)).
- Added S3 HTTPS integration test. [#12412](https://github.com/ClickHouse/ClickHouse/pull/12412) ([Pavel Kovalenko](https://github.com/Jokser)).
- Log sanitizer trap messages from separate thread. This will prevent possible deadlock under thread sanitizer. [#12313](https://github.com/ClickHouse/ClickHouse/pull/12313) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Now functional and stress tests will be able to run with old version of `clickhouse-test` script. [#12287](https://github.com/ClickHouse/ClickHouse/pull/12287) ([alesapin](https://github.com/alesapin)).
- Remove strange file creation during build in `orc`. [#12258](https://github.com/ClickHouse/ClickHouse/pull/12258) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Place common docker compose files to integration docker container. [#12168](https://github.com/ClickHouse/ClickHouse/pull/12168) ([Ilya Yatsishin](https://github.com/qoega)).
- Fix warnings from CodeQL. `CodeQL` is another static analyzer that we will use along with `clang-tidy` and `PVS-Studio` that we use already. [#12138](https://github.com/ClickHouse/ClickHouse/pull/12138) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Minor CMake fixes for UNBUNDLED build. [#12131](https://github.com/ClickHouse/ClickHouse/pull/12131) ([Matwey V. Kornilov](https://github.com/matwey)).
- Added a showcase of the minimal Docker image without using any Linux distribution. [#12126](https://github.com/ClickHouse/ClickHouse/pull/12126) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Perform an upgrade of system packages in the `clickhouse-server` docker image. [#12124](https://github.com/ClickHouse/ClickHouse/pull/12124) ([Ivan Blinkov](https://github.com/blinkov)).
- Add `UNBUNDLED` flag to `system.build_options` table. Move skip lists for `clickhouse-test` to clickhouse repo. [#12107](https://github.com/ClickHouse/ClickHouse/pull/12107) ([alesapin](https://github.com/alesapin)).
- Regular check by [Anchore Container Analysis](https://docs.anchore.com) security analysis tool that looks for [CVE](https://cve.mitre.org/) in `clickhouse-server` Docker image. Also confirms that `Dockerfile` is buildable. Runs daily on `master` and on pull-requests to `Dockerfile`. [#12102](https://github.com/ClickHouse/ClickHouse/pull/12102) ([Ivan Blinkov](https://github.com/blinkov)).
- Daily check by [GitHub CodeQL](https://securitylab.github.com/tools/codeql) security analysis tool that looks for [CWE](https://cwe.mitre.org/). [#12101](https://github.com/ClickHouse/ClickHouse/pull/12101) ([Ivan Blinkov](https://github.com/blinkov)).
- Install `ca-certificates` before the first `apt-get update` in Dockerfile. [#12095](https://github.com/ClickHouse/ClickHouse/pull/12095) ([Ivan Blinkov](https://github.com/blinkov)).

## ClickHouse release 20.5[​](#clickhouse-release-205 "Direct link to ClickHouse release 20.5")

### ClickHouse release v20.5.4.40-stable 2020-08-10[​](#clickhouse-release-v205440-stable-2020-08-10 "Direct link to ClickHouse release v20.5.4.40-stable 2020-08-10")