ClickHouse/docs/changelogs/v20.8.6.6-lts.md

### ClickHouse release v20.8.6.6-lts FIXME as compared to v20.8.5.45-lts

#### Bug Fix
* Backported in [#16494](https://github.com/ClickHouse/ClickHouse/issues/16494): 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)).
* Backported in [#16816](https://github.com/ClickHouse/ClickHouse/issues/16816): Fixed the inconsistent behaviour when a part of return data could be dropped because the set for its filtration wasn't created. [#16308](https://github.com/ClickHouse/ClickHouse/pull/16308) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#16506](https://github.com/ClickHouse/ClickHouse/issues/16506): 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)).
* Backported in [#16472](https://github.com/ClickHouse/ClickHouse/issues/16472): Fix DROP TABLE for Distributed (racy with INSERT). [#16409](https://github.com/ClickHouse/ClickHouse/pull/16409) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#16573](https://github.com/ClickHouse/ClickHouse/issues/16573): 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)).
* Backported in [#16552](https://github.com/ClickHouse/ClickHouse/issues/16552): 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 Kot](https://github.com/myrrc)).
* Backported in [#16823](https://github.com/ClickHouse/ClickHouse/issues/16823): Fixed [#16081](https://github.com/ClickHouse/ClickHouse/issues/16081). [#16613](https://github.com/ClickHouse/ClickHouse/pull/16613) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#16892](https://github.com/ClickHouse/ClickHouse/issues/16892): 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)).