2020 Changelog

#### Performance Improvement[​](#performance-improvement-5 "Direct link to Performance Improvement")

- Slightly optimize very short queries with `LowCardinality`. [#14129](https://github.com/ClickHouse/ClickHouse/pull/14129) ([Anton Popov](https://github.com/CurtizJ)).
- Enable parallel INSERTs for table engines `Null`, `Memory`, `Distributed` and `Buffer` when the setting `max_insert_threads` is set. [#14120](https://github.com/ClickHouse/ClickHouse/pull/14120) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fail fast if `max_rows_to_read` limit is exceeded on parts scan. The motivation behind this change is to skip ranges scan for all selected parts if it is clear that `max_rows_to_read` is already exceeded. The change is quite noticeable for queries over big number of parts. [#13677](https://github.com/ClickHouse/ClickHouse/pull/13677) ([Roman Khavronenko](https://github.com/hagen1778)).
- Slightly improve performance of aggregation by UInt8/UInt16 keys. [#13099](https://github.com/ClickHouse/ClickHouse/pull/13099) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Optimize `has()`, `indexOf()` and `countEqual()` functions for `Array(LowCardinality(T))` and constant right arguments. [#12550](https://github.com/ClickHouse/ClickHouse/pull/12550) ([myrrc](https://github.com/myrrc)).
- When performing trivial `INSERT SELECT` queries, automatically set `max_threads` to 1 or `max_insert_threads`, and set `max_block_size` to `min_insert_block_size_rows`. Related to [#5907](https://github.com/ClickHouse/ClickHouse/issues/5907). [#12195](https://github.com/ClickHouse/ClickHouse/pull/12195) ([flynn](https://github.com/ucasFL)).

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

- ClickHouse can work as MySQL replica - it is implemented by `MaterializeMySQL` database engine. Implements [#4006](https://github.com/ClickHouse/ClickHouse/issues/4006). [#10851](https://github.com/ClickHouse/ClickHouse/pull/10851) ([Winter Zhang](https://github.com/zhang2014)).
- Add types `Int128`, `Int256`, `UInt256` and related functions for them. Extend Decimals with Decimal256 (precision up to 76 digits). New types are under the setting `allow_experimental_bigint_types`. It is working extremely slow and bad. The implementation is incomplete. Please don't use this feature. [#13097](https://github.com/ClickHouse/ClickHouse/pull/13097) ([Artem Zuikov](https://github.com/4ertus2)).

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement-7 "Direct link to Build/Testing/Packaging Improvement")

- Added `clickhouse install` script, that is useful if you only have a single binary. [#13528](https://github.com/ClickHouse/ClickHouse/pull/13528) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Allow to run `clickhouse` binary without configuration. [#13515](https://github.com/ClickHouse/ClickHouse/pull/13515) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Enable check for typos in code with `codespell`. [#13513](https://github.com/ClickHouse/ClickHouse/pull/13513) [#13511](https://github.com/ClickHouse/ClickHouse/pull/13511) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Enable Shellcheck in CI as a linter of .sh tests. This closes [#13168](https://github.com/ClickHouse/ClickHouse/issues/13168). [#13530](https://github.com/ClickHouse/ClickHouse/pull/13530) [#13529](https://github.com/ClickHouse/ClickHouse/pull/13529) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add a CMake option to fail configuration instead of auto-reconfiguration, enabled by default. [#13687](https://github.com/ClickHouse/ClickHouse/pull/13687) ([Konstantin](https://github.com/podshumok)).
- Expose version of embedded tzdata via TZDATA\_VERSION in system.build\_options. [#13648](https://github.com/ClickHouse/ClickHouse/pull/13648) ([filimonov](https://github.com/filimonov)).
- Improve generation of system.time\_zones table during build. Closes [#14209](https://github.com/ClickHouse/ClickHouse/issues/14209). [#14215](https://github.com/ClickHouse/ClickHouse/pull/14215) ([filimonov](https://github.com/filimonov)).
- Build ClickHouse with the most fresh tzdata from package repository. [#13623](https://github.com/ClickHouse/ClickHouse/pull/13623) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add the ability to write js-style comments in skip\_list.json. [#14159](https://github.com/ClickHouse/ClickHouse/pull/14159) ([alesapin](https://github.com/alesapin)).
- Ensure that there is no copy-pasted GPL code. [#13514](https://github.com/ClickHouse/ClickHouse/pull/13514) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Switch tests docker images to use test-base parent. [#14167](https://github.com/ClickHouse/ClickHouse/pull/14167) ([Ilya Yatsishin](https://github.com/qoega)).
- Adding retry logic when bringing up docker-compose cluster; Increasing COMPOSE\_HTTP\_TIMEOUT. [#14112](https://github.com/ClickHouse/ClickHouse/pull/14112) ([vzakaznikov](https://github.com/vzakaznikov)).
- Enabled `system.text_log` in stress test to find more bugs. [#13855](https://github.com/ClickHouse/ClickHouse/pull/13855) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Testflows LDAP module: adding missing certificates and dhparam.pem for openldap4. [#13780](https://github.com/ClickHouse/ClickHouse/pull/13780) ([vzakaznikov](https://github.com/vzakaznikov)).
- ZooKeeper cannot work reliably in unit tests in CI infrastructure. Using unit tests for ZooKeeper interaction with real ZooKeeper is bad idea from the start (unit tests are not supposed to verify complex distributed systems). We already using integration tests for this purpose and they are better suited. [#13745](https://github.com/ClickHouse/ClickHouse/pull/13745) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Added docker image for style check. Added style check that all docker and docker compose files are located in docker directory. [#13724](https://github.com/ClickHouse/ClickHouse/pull/13724) ([Ilya Yatsishin](https://github.com/qoega)).
- Fix cassandra build on Mac OS. [#13708](https://github.com/ClickHouse/ClickHouse/pull/13708) ([Ilya Yatsishin](https://github.com/qoega)).
- Fix link error in shared build. [#13700](https://github.com/ClickHouse/ClickHouse/pull/13700) ([Amos Bird](https://github.com/amosbird)).
- Updating LDAP user authentication suite to check that it works with RBAC. [#13656](https://github.com/ClickHouse/ClickHouse/pull/13656) ([vzakaznikov](https://github.com/vzakaznikov)).
- Removed `-DENABLE_CURL_CLIENT` for `contrib/aws`. [#13628](https://github.com/ClickHouse/ClickHouse/pull/13628) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Increasing health-check timeouts for ClickHouse nodes and adding support to dump docker-compose logs if unhealthy containers found. [#13612](https://github.com/ClickHouse/ClickHouse/pull/13612) ([vzakaznikov](https://github.com/vzakaznikov)).
- Make sure [#10977](https://github.com/ClickHouse/ClickHouse/issues/10977) is invalid. [#13539](https://github.com/ClickHouse/ClickHouse/pull/13539) ([Amos Bird](https://github.com/amosbird)).
- Skip PR's from robot-clickhouse. [#13489](https://github.com/ClickHouse/ClickHouse/pull/13489) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Move Dockerfiles from integration tests to `docker/test` directory. docker\_compose files are available in `runner` docker container. Docker images are built in CI and not in integration tests. [#13448](https://github.com/ClickHouse/ClickHouse/pull/13448) ([Ilya Yatsishin](https://github.com/qoega)).

## ClickHouse release 20.7[​](#clickhouse-release-207 "Direct link to ClickHouse release 20.7")

### ClickHouse release v20.7.2.30-stable, 2020-08-31[​](#clickhouse-release-v207230-stable-2020-08-31 "Direct link to ClickHouse release v20.7.2.30-stable, 2020-08-31")

#### Backward Incompatible Change[​](#backward-incompatible-change-5 "Direct link to Backward Incompatible Change")