2020 Changelog

- Try to connect to all shards in cluster when getting structure of remote table and skip\_unavailable\_shards is set. [#7278](https://github.com/ClickHouse/ClickHouse/pull/7278) ([nvartolomei](https://github.com/nvartolomei))
- Add `total_rows`/`total_bytes` into the `system.tables` table. [#9919](https://github.com/ClickHouse/ClickHouse/pull/9919) ([Azat Khuzhin](https://github.com/azat))
- System log tables now use polymorpic parts by default. [#9905](https://github.com/ClickHouse/ClickHouse/pull/9905) ([Anton Popov](https://github.com/CurtizJ))
- Add type column into system.settings/merge\_tree\_settings [#9909](https://github.com/ClickHouse/ClickHouse/pull/9909) ([Azat Khuzhin](https://github.com/azat))
- Check for available CPU instructions at server startup as early as possible. [#9888](https://github.com/ClickHouse/ClickHouse/pull/9888) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Remove `ORDER BY` stage from mutations because we read from a single ordered part in a single thread. Also add check that the rows in mutation are ordered by sorting key and this order is not violated. [#9886](https://github.com/ClickHouse/ClickHouse/pull/9886) ([alesapin](https://github.com/alesapin))
- Implement operator LIKE for FixedString at left hand side. This is needed to better support TPC-DS queries. [#9890](https://github.com/ClickHouse/ClickHouse/pull/9890) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Add `force_optimize_skip_unused_shards_no_nested` that will disable `force_optimize_skip_unused_shards` for nested Distributed table [#9812](https://github.com/ClickHouse/ClickHouse/pull/9812) ([Azat Khuzhin](https://github.com/azat))
- Now columns size is calculated only once for MergeTree data parts. [#9827](https://github.com/ClickHouse/ClickHouse/pull/9827) ([alesapin](https://github.com/alesapin))
- Evaluate constant expressions for `optimize_skip_unused_shards` (i.e. `SELECT * FROM foo_dist WHERE key=xxHash32(0)`) [#8846](https://github.com/ClickHouse/ClickHouse/pull/8846) ([Azat Khuzhin](https://github.com/azat))
- Check for using `Date` or `DateTime` column from TTL expressions was removed. [#9967](https://github.com/ClickHouse/ClickHouse/pull/9967) ([Vladimir Chebotarev](https://github.com/excitoon))
- DiskS3 hard links optimal implementation. [#9760](https://github.com/ClickHouse/ClickHouse/pull/9760) ([Pavel Kovalenko](https://github.com/Jokser))
- If `set multiple_joins_rewriter_version = 2` enables second version of multiple JOIN rewrites that keeps not clashed column names as is. It supports multiple JOINs with `USING` and allow `select *` for JOINs with subqueries. [#9739](https://github.com/ClickHouse/ClickHouse/pull/9739) ([Artem Zuikov](https://github.com/4ertus2))
- Implementation of "non-blocking" alter for StorageMergeTree [#9606](https://github.com/ClickHouse/ClickHouse/pull/9606) ([alesapin](https://github.com/alesapin))
- Add MergeTree full support for DiskS3 [#9646](https://github.com/ClickHouse/ClickHouse/pull/9646) ([Pavel Kovalenko](https://github.com/Jokser))
- Extend `splitByString` to support empty strings as separators. [#9742](https://github.com/ClickHouse/ClickHouse/pull/9742) ([hcz](https://github.com/hczhcz))
- Add a `timestamp_ns` column to `system.trace_log`. It contains a high-definition timestamp of the trace event, and allows to build timelines of thread profiles ("flame charts"). [#9696](https://github.com/ClickHouse/ClickHouse/pull/9696) ([Alexander Kuzmenkov](https://github.com/akuzm))
- When the setting `send_logs_level` is enabled, avoid intermixing of log messages and query progress. [#9634](https://github.com/ClickHouse/ClickHouse/pull/9634) ([Azat Khuzhin](https://github.com/azat))
- Added support of `MATERIALIZE TTL IN PARTITION`. [#9581](https://github.com/ClickHouse/ClickHouse/pull/9581) ([Vladimir Chebotarev](https://github.com/excitoon))
- Support complex types inside Avro nested fields [#10502](https://github.com/ClickHouse/ClickHouse/pull/10502) ([Andrew Onyshchuk](https://github.com/oandrew))