2020 Changelog

- Implement `ALTER MODIFY/DROP` queries on top of mutations for `ReplicatedMergeTree*` engines family. Now `ALTERS` blocks only at the metadata update stage, and don't block after that. [#8701](https://github.com/ClickHouse/ClickHouse/pull/8701) ([alesapin](https://github.com/alesapin))
- Add ability to rewrite CROSS to INNER JOINs with `WHERE` section containing unqialified names. [#9512](https://github.com/ClickHouse/ClickHouse/pull/9512) ([Artem Zuikov](https://github.com/4ertus2))
- Make `SHOW TABLES` and `SHOW DATABASES` queries support the `WHERE` expressions and `FROM`/`IN` [#9076](https://github.com/ClickHouse/ClickHouse/pull/9076) ([sundyli](https://github.com/sundy-li))
- Added a setting `deduplicate_blocks_in_dependent_materialized_views`. [#9070](https://github.com/ClickHouse/ClickHouse/pull/9070) ([urykhy](https://github.com/urykhy))
- After recent changes MySQL client started to print binary strings in hex thereby making them not readable ([#9032](https://github.com/ClickHouse/ClickHouse/issues/9032)). The workaround in ClickHouse is to mark string columns as UTF-8, which is not always, but usually the case. [#9079](https://github.com/ClickHouse/ClickHouse/pull/9079) ([Yuriy Baranov](https://github.com/yurriy))
- Add support of String and FixedString keys for `sumMap` [#8903](https://github.com/ClickHouse/ClickHouse/pull/8903) ([Baudouin Giard](https://github.com/bgiard))
- Support string keys in SummingMergeTree maps [#8933](https://github.com/ClickHouse/ClickHouse/pull/8933) ([Baudouin Giard](https://github.com/bgiard))
- Signal termination of thread to the thread pool even if the thread has thrown exception [#8736](https://github.com/ClickHouse/ClickHouse/pull/8736) ([Ding Xiang Fei](https://github.com/dingxiangfei2009))
- Allow to set `query_id` in `clickhouse-benchmark` [#9416](https://github.com/ClickHouse/ClickHouse/pull/9416) ([Anton Popov](https://github.com/CurtizJ))
- Don't allow strange expressions in `ALTER TABLE ... PARTITION partition` query. This addresses [#7192](https://github.com/ClickHouse/ClickHouse/issues/7192) [#8835](https://github.com/ClickHouse/ClickHouse/pull/8835) ([alexey-milovidov](https://github.com/alexey-milovidov))
- The table `system.table_engines` now provides information about feature support (like `supports_ttl` or `supports_sort_order`). [#8830](https://github.com/ClickHouse/ClickHouse/pull/8830) ([Max Akhmedov](https://github.com/zlobober))
- Enable `system.metric_log` by default. It will contain rows with values of ProfileEvents, CurrentMetrics collected with "collect\_interval\_milliseconds" interval (one second by default). The table is very small (usually in order of megabytes) and collecting this data by default is reasonable. [#9225](https://github.com/ClickHouse/ClickHouse/pull/9225) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Initialize query profiler for all threads in a group, e.g. it allows to fully profile insert-queries. Fixes [#6964](https://github.com/ClickHouse/ClickHouse/issues/6964) [#8874](https://github.com/ClickHouse/ClickHouse/pull/8874) ([Ivan](https://github.com/abyss7))
- Now temporary `LIVE VIEW` is created by `CREATE LIVE VIEW name WITH TIMEOUT [42] ...` instead of `CREATE TEMPORARY LIVE VIEW ...`, because the previous syntax was not consistent with `CREATE TEMPORARY TABLE ...` [#9131](https://github.com/ClickHouse/ClickHouse/pull/9131) ([tavplubix](https://github.com/tavplubix))
- Add text\_log.level configuration parameter to limit entries that goes to `system.text_log` table [#8809](https://github.com/ClickHouse/ClickHouse/pull/8809) ([Azat Khuzhin](https://github.com/azat))
- Allow to put downloaded part to a disks/volumes according to TTL rules [#8598](https://github.com/ClickHouse/ClickHouse/pull/8598) ([Vladimir Chebotarev](https://github.com/excitoon))
- For external MySQL dictionaries, allow to mutualize MySQL connection pool to "share" them among dictionaries. This option significantly reduces the number of connections to MySQL servers. [#9409](https://github.com/ClickHouse/ClickHouse/pull/9409) ([Clément Rodriguez](https://github.com/clemrodriguez))
- Show nearest query execution time for quantiles in `clickhouse-benchmark` output instead of interpolated values. It's better to show values that correspond to the execution time of some queries. [#8712](https://github.com/ClickHouse/ClickHouse/pull/8712) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Possibility to add key & timestamp for the message when inserting data to Kafka. Fixes [#7198](https://github.com/ClickHouse/ClickHouse/issues/7198) [#8969](https://github.com/ClickHouse/ClickHouse/pull/8969) ([filimonov](https://github.com/filimonov))
- If server is run from terminal, highlight thread number, query id and log priority by colors. This is for improved readability of correlated log messages for developers. [#8961](https://github.com/ClickHouse/ClickHouse/pull/8961) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Better exception message while loading tables for `Ordinary` database. [#9527](https://github.com/ClickHouse/ClickHouse/pull/9527) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Implement `arraySlice` for arrays with aggregate function states. This fixes [#9388](https://github.com/ClickHouse/ClickHouse/issues/9388) [#9391](https://github.com/ClickHouse/ClickHouse/pull/9391) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Allow constant functions and constant arrays to be used on the right side of IN operator. [#8813](https://github.com/ClickHouse/ClickHouse/pull/8813) ([Anton Popov](https://github.com/CurtizJ))
- If zookeeper exception has happened while fetching data for system.replicas, display it in a separate column. This implements [#9137](https://github.com/ClickHouse/ClickHouse/issues/9137) [#9138](https://github.com/ClickHouse/ClickHouse/pull/9138) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Atomically remove MergeTree data parts on destroy. [#8402](https://github.com/ClickHouse/ClickHouse/pull/8402) ([Vladimir Chebotarev](https://github.com/excitoon))
- Support row-level security for Distributed tables. [#8926](https://github.com/ClickHouse/ClickHouse/pull/8926) ([Ivan](https://github.com/abyss7))
- Now we recognize suffix (like KB, KiB...) in settings values. [#8072](https://github.com/ClickHouse/ClickHouse/pull/8072) ([Mikhail Korotov](https://github.com/millb))
- Prevent out of memory while constructing result of a large JOIN. [#8637](https://github.com/ClickHouse/ClickHouse/pull/8637) ([Artem Zuikov](https://github.com/4ertus2))
- Added names of clusters to suggestions in interactive mode in `clickhouse-client`. [#8709](https://github.com/ClickHouse/ClickHouse/pull/8709) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Initialize query profiler for all threads in a group, e.g. it allows to fully profile insert-queries [#8820](https://github.com/ClickHouse/ClickHouse/pull/8820) ([Ivan](https://github.com/abyss7))
- Added column `exception_code` in `system.query_log` table. [#8770](https://github.com/ClickHouse/ClickHouse/pull/8770) ([Mikhail Korotov](https://github.com/millb))
- Enabled MySQL compatibility server on port `9004` in the default server configuration file. Fixed password generation command in the example in configuration. [#8771](https://github.com/ClickHouse/ClickHouse/pull/8771) ([Yuriy Baranov](https://github.com/yurriy))
- Prevent abort on shutdown if the filesystem is readonly. This fixes [#9094](https://github.com/ClickHouse/ClickHouse/issues/9094) [#9100](https://github.com/ClickHouse/ClickHouse/pull/9100) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Better exception message when length is required in HTTP POST query. [#9453](https://github.com/ClickHouse/ClickHouse/pull/9453) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Add `_path` and `_file` virtual columns to `HDFS` and `File` engines and `hdfs` and `file` table functions [#8489](https://github.com/ClickHouse/ClickHouse/pull/8489) ([Olga Khvostikova](https://github.com/stavrolia))