2021 Changelog

- Increase `max_uri_size` (the maximum size of URL in HTTP interface) to 1 MiB by default. This closes [#21197](https://github.com/ClickHouse/ClickHouse/issues/21197). [#22997](https://github.com/ClickHouse/ClickHouse/pull/22997) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Set `background_fetches_pool_size` to `8` that is better for production usage with frequent small insertions or slow ZooKeeper cluster. [#22945](https://github.com/ClickHouse/ClickHouse/pull/22945) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- FlatDictionary added `initial_array_size`, `max_array_size` options. [#22521](https://github.com/ClickHouse/ClickHouse/pull/22521) ([Maksim Kita](https://github.com/kitaisreal)).
- Add new setting `non_replicated_deduplication_window` for non-replicated MergeTree inserts deduplication. [#22514](https://github.com/ClickHouse/ClickHouse/pull/22514) ([alesapin](https://github.com/alesapin)).
- Update paths to the `CatBoost` model configs in config reloading. [#22434](https://github.com/ClickHouse/ClickHouse/pull/22434) ([Kruglov Pavel](https://github.com/Avogar)).
- Added `Decimal256` type support in dictionaries. `Decimal256` is experimental feature. Closes [#20979](https://github.com/ClickHouse/ClickHouse/issues/20979). [#22960](https://github.com/ClickHouse/ClickHouse/pull/22960) ([Maksim Kita](https://github.com/kitaisreal)).
- Enabled `async_socket_for_remote` by default (using less amount of OS threads for distributed queries). [#23683](https://github.com/ClickHouse/ClickHouse/pull/23683) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Fixed `quantile(s)TDigest`. Added special handling of singleton centroids according to tdunning/t-digest 3.2+. Also a bug with over-compression of centroids in implementation of earlier version of the algorithm was fixed. [#23314](https://github.com/ClickHouse/ClickHouse/pull/23314) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Make function name `unhex` case insensitive for compatibility with MySQL. [#23229](https://github.com/ClickHouse/ClickHouse/pull/23229) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Implement functions `arrayHasAny`, `arrayHasAll`, `has`, `indexOf`, `countEqual` for generic case when types of array elements are different. In previous versions the functions `arrayHasAny`, `arrayHasAll` returned false and `has`, `indexOf`, `countEqual` thrown exception. Also add support for `Decimal` and big integer types in functions `has` and similar. This closes [#20272](https://github.com/ClickHouse/ClickHouse/issues/20272). [#23044](https://github.com/ClickHouse/ClickHouse/pull/23044) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Raised the threshold on max number of matches in result of the function `extractAllGroupsHorizontal`. [#23036](https://github.com/ClickHouse/ClickHouse/pull/23036) ([Vasily Nemkov](https://github.com/Enmk)).
- Do not perform `optimize_skip_unused_shards` for cluster with one node. [#22999](https://github.com/ClickHouse/ClickHouse/pull/22999) ([Azat Khuzhin](https://github.com/azat)).
- Added ability to run clickhouse-keeper (experimental drop-in replacement to ZooKeeper) with SSL. Config settings `keeper_server.tcp_port_secure` can be used for secure interaction between client and keeper-server. `keeper_server.raft_configuration.secure` can be used to enable internal secure communication between nodes. [#22992](https://github.com/ClickHouse/ClickHouse/pull/22992) ([alesapin](https://github.com/alesapin)).
- Added ability to flush buffer only in background for `Buffer` tables. [#22986](https://github.com/ClickHouse/ClickHouse/pull/22986) ([Azat Khuzhin](https://github.com/azat)).
- When selecting from MergeTree table with NULL in WHERE condition, in rare cases, exception was thrown. This closes [#20019](https://github.com/ClickHouse/ClickHouse/issues/20019). [#22978](https://github.com/ClickHouse/ClickHouse/pull/22978) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix error handling in Poco HTTP Client for AWS. [#22973](https://github.com/ClickHouse/ClickHouse/pull/22973) ([kreuzerkrieg](https://github.com/kreuzerkrieg)).
- Respect `max_part_removal_threads` for `ReplicatedMergeTree`. [#22971](https://github.com/ClickHouse/ClickHouse/pull/22971) ([Azat Khuzhin](https://github.com/azat)).
- Fix obscure corner case of MergeTree settings inactive\_parts\_to\_throw\_insert = 0 with inactive\_parts\_to\_delay\_insert > 0. [#22947](https://github.com/ClickHouse/ClickHouse/pull/22947) ([Azat Khuzhin](https://github.com/azat)).
- `dateDiff` now works with `DateTime64` arguments (even for values outside of `DateTime` range) [#22931](https://github.com/ClickHouse/ClickHouse/pull/22931) ([Vasily Nemkov](https://github.com/Enmk)).
- MaterializeMySQL (experimental feature): added an ability to replicate MySQL databases containing views without failing. This is accomplished by ignoring the views. [#22760](https://github.com/ClickHouse/ClickHouse/pull/22760) ([Christian](https://github.com/cfroystad)).
- Allow RBAC row policy via postgresql protocol. Closes [#22658](https://github.com/ClickHouse/ClickHouse/issues/22658). PostgreSQL protocol is enabled in configuration by default. [#22755](https://github.com/ClickHouse/ClickHouse/pull/22755) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add metric to track how much time is spend during waiting for Buffer layer lock. [#22725](https://github.com/ClickHouse/ClickHouse/pull/22725) ([Azat Khuzhin](https://github.com/azat)).
- Allow to use CTE in VIEW definition. This closes [#22491](https://github.com/ClickHouse/ClickHouse/issues/22491). [#22657](https://github.com/ClickHouse/ClickHouse/pull/22657) ([Amos Bird](https://github.com/amosbird)).
- Clear the rest of the screen and show cursor in `clickhouse-client` if previous program has left garbage in terminal. This closes [#16518](https://github.com/ClickHouse/ClickHouse/issues/16518). [#22634](https://github.com/ClickHouse/ClickHouse/pull/22634) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Make `round` function to behave consistently on non-x86\_64 platforms. Rounding half to nearest even (Banker's rounding) is used. [#22582](https://github.com/ClickHouse/ClickHouse/pull/22582) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Correctly check structure of blocks of data that are sending by Distributed tables. [#22325](https://github.com/ClickHouse/ClickHouse/pull/22325) ([Azat Khuzhin](https://github.com/azat)).
- Allow publishing Kafka errors to a virtual column of Kafka engine, controlled by the `kafka_handle_error_mode` setting. [#21850](https://github.com/ClickHouse/ClickHouse/pull/21850) ([fastio](https://github.com/fastio)).
- Add aliases `simpleJSONExtract/simpleJSONHas` to `visitParam/visitParamExtract{UInt, Int, Bool, Float, Raw, String}`. Fixes [#21383](https://github.com/ClickHouse/ClickHouse/issues/21383). [#21519](https://github.com/ClickHouse/ClickHouse/pull/21519) ([fastio](https://github.com/fastio)).
- Add `clickhouse-library-bridge` for library dictionary source. Closes [#9502](https://github.com/ClickHouse/ClickHouse/issues/9502). [#21509](https://github.com/ClickHouse/ClickHouse/pull/21509) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Forbid to drop a column if it's referenced by materialized view. Closes [#21164](https://github.com/ClickHouse/ClickHouse/issues/21164). [#21303](https://github.com/ClickHouse/ClickHouse/pull/21303) ([flynn](https://github.com/ucasFL)).
- Support dynamic interserver credentials (rotating credentials without downtime). [#14113](https://github.com/ClickHouse/ClickHouse/pull/14113) ([johnskopis](https://github.com/johnskopis)).
- Add support for Kafka storage with `Arrow` and `ArrowStream` format messages. [#23415](https://github.com/ClickHouse/ClickHouse/pull/23415) ([Chao Ma](https://github.com/godliness)).
- Fixed missing semicolon in exception message. The user may find this exception message unpleasant to read. [#23208](https://github.com/ClickHouse/ClickHouse/pull/23208) ([alexey-milovidov](https://github.com/alexey-milovidov)).