2020 Changelog

### ClickHouse release v20.10.4.1-stable, 2020-11-13[​](#clickhouse-release-v201041-stable-2020-11-13 "Direct link to ClickHouse release v20.10.4.1-stable, 2020-11-13")

#### Bug Fix[​](#bug-fix-8 "Direct link to Bug Fix")

- Fix rare silent crashes when query profiler is on and ClickHouse is installed on OS with glibc version that has (supposedly) broken asynchronous unwind tables for some functions. This fixes [#15301](https://github.com/ClickHouse/ClickHouse/issues/15301). This fixes [#13098](https://github.com/ClickHouse/ClickHouse/issues/13098). [#16846](https://github.com/ClickHouse/ClickHouse/pull/16846) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix `IN` operator over several columns and tuples with enabled `transform_null_in` setting. Fixes [#15310](https://github.com/ClickHouse/ClickHouse/issues/15310). [#16722](https://github.com/ClickHouse/ClickHouse/pull/16722) ([Anton Popov](https://github.com/CurtizJ)).
- This will fix optimize\_read\_in\_order/optimize\_aggregation\_in\_order with max\_threads>0 and expression in ORDER BY. [#16637](https://github.com/ClickHouse/ClickHouse/pull/16637) ([Azat Khuzhin](https://github.com/azat)).
- Now when parsing AVRO from input the LowCardinality is removed from type. Fixes [#16188](https://github.com/ClickHouse/ClickHouse/issues/16188). [#16521](https://github.com/ClickHouse/ClickHouse/pull/16521) ([Mike](https://github.com/myrrc)).
- Fix rapid growth of metadata when using MySQL Master -> MySQL Slave -> ClickHouse MaterializeMySQL Engine, and `slave_parallel_worker` enabled on MySQL Slave, by properly shrinking GTID sets. This fixes [#15951](https://github.com/ClickHouse/ClickHouse/issues/15951). [#16504](https://github.com/ClickHouse/ClickHouse/pull/16504) ([TCeason](https://github.com/TCeason)).
- Fix DROP TABLE for Distributed (racy with INSERT). [#16409](https://github.com/ClickHouse/ClickHouse/pull/16409) ([Azat Khuzhin](https://github.com/azat)).
- Fix processing of very large entries in replication queue. Very large entries may appear in ALTER queries if table structure is extremely large (near 1 MB). This fixes [#16307](https://github.com/ClickHouse/ClickHouse/issues/16307). [#16332](https://github.com/ClickHouse/ClickHouse/pull/16332) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix bug with MySQL database. When MySQL server used as database engine is down some queries raise Exception, because they try to get tables from disabled server, while it's unnecessary. For example, query `SELECT ... FROM system.parts` should work only with MergeTree tables and don't touch MySQL database at all. [#16032](https://github.com/ClickHouse/ClickHouse/pull/16032) ([Kruglov Pavel](https://github.com/Avogar)).

#### Improvement[​](#improvement-3 "Direct link to Improvement")

- Workaround for use S3 with nginx server as proxy. Nginx currenty does not accept urls with empty path like <http://domain.com?delete>, but vanilla aws-sdk-cpp produces this kind of urls. This commit uses patched aws-sdk-cpp version, which makes urls with "/" as path in this cases, like <http://domain.com/?delete>. [#16813](https://github.com/ClickHouse/ClickHouse/pull/16813) ([ianton-ru](https://github.com/ianton-ru)).

### ClickHouse release v20.10.3.30, 2020-10-28[​](#clickhouse-release-v2010330-2020-10-28 "Direct link to ClickHouse release v20.10.3.30, 2020-10-28")

#### Backward Incompatible Change[​](#backward-incompatible-change-2 "Direct link to Backward Incompatible Change")

- Make `multiple_joins_rewriter_version` obsolete. Remove first version of joins rewriter. [#15472](https://github.com/ClickHouse/ClickHouse/pull/15472) ([Artem Zuikov](https://github.com/4ertus2)).
- Change default value of `format_regexp_escaping_rule` setting (it's related to `Regexp` format) to `Raw` (it means - read whole subpattern as a value) to make the behaviour more like to what users expect. [#15426](https://github.com/ClickHouse/ClickHouse/pull/15426) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add support for nested multiline comments `/* comment /* comment */ */` in SQL. This conforms to the SQL standard. [#14655](https://github.com/ClickHouse/ClickHouse/pull/14655) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Added MergeTree settings (`max_replicated_merges_with_ttl_in_queue` and `max_number_of_merges_with_ttl_in_pool`) to control the number of merges with TTL in the background pool and replicated queue. This change breaks compatibility with older versions only if you use delete TTL. Otherwise, replication will stay compatible. You can avoid incompatibility issues if you update all shard replicas at once or execute `SYSTEM STOP TTL MERGES` until you finish the update of all replicas. If you'll get an incompatible entry in the replication queue, first of all, execute `SYSTEM STOP TTL MERGES` and after `ALTER TABLE ... DETACH PARTITION ...` the partition where incompatible TTL merge was assigned. Attach it back on a single replica. [#14490](https://github.com/ClickHouse/ClickHouse/pull/14490) ([alesapin](https://github.com/alesapin)).
- When upgrading from versions older than 20.5, if rolling update is performed and cluster contains both versions 20.5 or greater and less than 20.5, if ClickHouse nodes with old versions are restarted and old version has been started up in presence of newer versions, it may lead to `Part ... intersects previous part` errors. To prevent this error, first install newer clickhouse-server packages on all cluster nodes and then do restarts (so, when clickhouse-server is restarted, it will start up with the new version).

#### New Feature[​](#new-feature-2 "Direct link to New Feature")