2021 Changelog

- `mapPopulatesSeries` function supports `Map` type. [#26663](https://github.com/ClickHouse/ClickHouse/pull/26663) ([Ildus Kurbangaliev](https://github.com/ildus)).
- Fix excessive (x2) connect attempts with `skip_unavailable_shards`. [#26658](https://github.com/ClickHouse/ClickHouse/pull/26658) ([Azat Khuzhin](https://github.com/azat)).
- Avoid hanging `clickhouse-benchmark` if connection fails (i.e. on EMFILE). [#26656](https://github.com/ClickHouse/ClickHouse/pull/26656) ([Azat Khuzhin](https://github.com/azat)).
- Allow more threads to be used by the Kafka engine. [#26642](https://github.com/ClickHouse/ClickHouse/pull/26642) ([feihengye](https://github.com/feihengye)).
- Add round-robin support for `clickhouse-benchmark` (it does not differ from the regular multi host/port run except for statistics report). [#26607](https://github.com/ClickHouse/ClickHouse/pull/26607) ([Azat Khuzhin](https://github.com/azat)).
- Executable dictionaries (`executable`, `executable_pool`) enable creation with DDL query using `clickhouse-local`. Closes [#22355](https://github.com/ClickHouse/ClickHouse/issues/22355). [#26510](https://github.com/ClickHouse/ClickHouse/pull/26510) ([Maksim Kita](https://github.com/kitaisreal)).
- Set client query kind for `mysql` and `postgresql` compatibility protocol handlers. [#26498](https://github.com/ClickHouse/ClickHouse/pull/26498) ([anneji-dev](https://github.com/anneji-dev)).
- Apply `LIMIT` on the shards for queries like `SELECT * FROM dist ORDER BY key LIMIT 10` w/ `distributed_push_down_limit=1`. Avoid running `Distinct`/`LIMIT BY` steps for queries like `SELECT DISTINCT shading_key FROM dist ORDER BY key`. Now `distributed_push_down_limit` is respected by `optimize_distributed_group_by_sharding_key` optimization. [#26466](https://github.com/ClickHouse/ClickHouse/pull/26466) ([Azat Khuzhin](https://github.com/azat)).
- Updated protobuf to 3.17.3. Changelogs are available on <https://github.com/protocolbuffers/protobuf/releases>. [#26424](https://github.com/ClickHouse/ClickHouse/pull/26424) ([Ilya Yatsishin](https://github.com/qoega)).
- Enable `use_hedged_requests` setting that allows to mitigate tail latencies on large clusters. [#26380](https://github.com/ClickHouse/ClickHouse/pull/26380) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Improve behaviour with non-existing host in user allowed host list. [#26368](https://github.com/ClickHouse/ClickHouse/pull/26368) ([ianton-ru](https://github.com/ianton-ru)).
- Add ability to set `Distributed` directory monitor settings via CREATE TABLE (i.e. `CREATE TABLE dist (key Int) Engine=Distributed(cluster, db, table) SETTINGS monitor_batch_inserts=1` and similar). [#26336](https://github.com/ClickHouse/ClickHouse/pull/26336) ([Azat Khuzhin](https://github.com/azat)).
- Save server address in history URLs in web UI if it differs from the origin of web UI. This closes [#26044](https://github.com/ClickHouse/ClickHouse/issues/26044). [#26322](https://github.com/ClickHouse/ClickHouse/pull/26322) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add events to profile calls to `sleep` / `sleepEachRow`. [#26320](https://github.com/ClickHouse/ClickHouse/pull/26320) ([Raúl Marín](https://github.com/Algunenano)).
- Allow to reuse connections of shards among different clusters. It also avoids creating new connections when using `cluster` table function. [#26318](https://github.com/ClickHouse/ClickHouse/pull/26318) ([Amos Bird](https://github.com/amosbird)).
- Control the execution period of clear old temporary directories by parameter with default value. [#26212](https://github.com/ClickHouse/ClickHouse/issues/26212). [#26313](https://github.com/ClickHouse/ClickHouse/pull/26313) ([fastio](https://github.com/fastio)).
- Add a setting `function_range_max_elements_in_block` to tune the safety threshold for data volume generated by function `range`. This closes [#26303](https://github.com/ClickHouse/ClickHouse/issues/26303). [#26305](https://github.com/ClickHouse/ClickHouse/pull/26305) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Check hash function at table creation, not at sampling. Add settings for MergeTree, if someone create a table with incorrect sampling column but sampling never be used, disable this settings for starting the server without exception. [#26256](https://github.com/ClickHouse/ClickHouse/pull/26256) ([zhaoyu](https://github.com/zxc111)).
- Added `output_format_avro_string_column_pattern` setting to put specified String columns to Avro as string instead of default bytes. Implements [#22414](https://github.com/ClickHouse/ClickHouse/issues/22414). [#26245](https://github.com/ClickHouse/ClickHouse/pull/26245) ([Ilya Golshtein](https://github.com/ilejn)).
- Add information about column sizes in `system.columns` table for `Log` and `TinyLog` tables. This closes [#9001](https://github.com/ClickHouse/ClickHouse/issues/9001). [#26241](https://github.com/ClickHouse/ClickHouse/pull/26241) ([Nikolay Degterinsky](https://github.com/evillique)).
- Don't throw exception when querying `system.detached_parts` table if there is custom disk configuration and `detached` directory does not exist on some disks. This closes [#26078](https://github.com/ClickHouse/ClickHouse/issues/26078). [#26236](https://github.com/ClickHouse/ClickHouse/pull/26236) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Check for non-deterministic functions in keys, including constant expressions like `now()`, `today()`. This closes [#25875](https://github.com/ClickHouse/ClickHouse/issues/25875). This closes [#11333](https://github.com/ClickHouse/ClickHouse/issues/11333). [#26235](https://github.com/ClickHouse/ClickHouse/pull/26235) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- convert timestamp and timestamptz data types to `DateTime64` in PostgreSQL table engine. [#26234](https://github.com/ClickHouse/ClickHouse/pull/26234) ([jasine](https://github.com/jasine)).
- Apply aggressive IN index analysis for projections so that better projection candidate can be selected. [#26218](https://github.com/ClickHouse/ClickHouse/pull/26218) ([Amos Bird](https://github.com/amosbird)).
- Remove GLOBAL keyword for IN when scalar function is passed. In previous versions, if user specified `GLOBAL IN f(x)` exception was thrown. [#26217](https://github.com/ClickHouse/ClickHouse/pull/26217) ([Amos Bird](https://github.com/amosbird)).
- Add error id (like `BAD_ARGUMENTS`) to exception messages. This closes [#25862](https://github.com/ClickHouse/ClickHouse/issues/25862). [#26172](https://github.com/ClickHouse/ClickHouse/pull/26172) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix incorrect output with --progress option for clickhouse-local. Progress bar will be cleared once it gets to 100% - same as it is done for clickhouse-client. Closes [#17484](https://github.com/ClickHouse/ClickHouse/issues/17484). [#26128](https://github.com/ClickHouse/ClickHouse/pull/26128) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add `merge_selecting_sleep_ms` setting. [#26120](https://github.com/ClickHouse/ClickHouse/pull/26120) ([lthaooo](https://github.com/lthaooo)).
- Remove complicated usage of Linux AIO with one block readahead and replace it with plain simple synchronous IO with O\_DIRECT. In previous versions, the setting `min_bytes_to_use_direct_io` may not work correctly if `max_threads` is greater than one. Reading with direct IO (that is disabled by default for queries and enabled by default for large merges) will work in less efficient way. This closes [#25997](https://github.com/ClickHouse/ClickHouse/issues/25997). [#26003](https://github.com/ClickHouse/ClickHouse/pull/26003) ([alexey-milovidov](https://github.com/alexey-milovidov)).