2020 Changelog

- Fix the case when memory can be overallocated regardless to the limit. This closes [#14560](https://github.com/ClickHouse/ClickHouse/issues/14560). [#16206](https://github.com/ClickHouse/ClickHouse/pull/16206) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix `executable` dictionary source hang. In previous versions, when using some formats (e.g. `JSONEachRow`) data was not feed to a child process before it outputs at least something. This closes [#1697](https://github.com/ClickHouse/ClickHouse/issues/1697). This closes [#2455](https://github.com/ClickHouse/ClickHouse/issues/2455). [#14525](https://github.com/ClickHouse/ClickHouse/pull/14525) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix double free in case of exception in function `dictGet`. It could have happened if dictionary was loaded with error. [#16429](https://github.com/ClickHouse/ClickHouse/pull/16429) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Fix group by with totals/rollup/cube modifers and min/max functions over group by keys. Fixes [#16393](https://github.com/ClickHouse/ClickHouse/issues/16393). [#16397](https://github.com/ClickHouse/ClickHouse/pull/16397) ([Anton Popov](https://github.com/CurtizJ)).
- Fix async Distributed INSERT with prefer\_localhost\_replica=0 and internal\_replication. [#16358](https://github.com/ClickHouse/ClickHouse/pull/16358) ([Azat Khuzhin](https://github.com/azat)).
- Fix a very wrong code in TwoLevelStringHashTable implementation, which might lead to memory leak. [#16264](https://github.com/ClickHouse/ClickHouse/pull/16264) ([Amos Bird](https://github.com/amosbird)).
- Fix segfault in some cases of wrong aggregation in lambdas. [#16082](https://github.com/ClickHouse/ClickHouse/pull/16082) ([Anton Popov](https://github.com/CurtizJ)).
- Fix `ALTER MODIFY ... ORDER BY` query hang for `ReplicatedVersionedCollapsingMergeTree`. This fixes [#15980](https://github.com/ClickHouse/ClickHouse/issues/15980). [#16011](https://github.com/ClickHouse/ClickHouse/pull/16011) ([alesapin](https://github.com/alesapin)).
- `MaterializeMySQL` (experimental feature): Fix collate name & charset name parser and support `length = 0` for string type. [#16008](https://github.com/ClickHouse/ClickHouse/pull/16008) ([Winter Zhang](https://github.com/zhang2014)).
- Allow to use `direct` layout for dictionaries with complex keys. [#16007](https://github.com/ClickHouse/ClickHouse/pull/16007) ([Anton Popov](https://github.com/CurtizJ)).
- Prevent replica hang for 5-10 mins when replication error happens after a period of inactivity. [#15987](https://github.com/ClickHouse/ClickHouse/pull/15987) ([filimonov](https://github.com/filimonov)).
- Fix rare segfaults when inserting into or selecting from MaterializedView and concurrently dropping target table (for Atomic database engine). [#15984](https://github.com/ClickHouse/ClickHouse/pull/15984) ([tavplubix](https://github.com/tavplubix)).
- Fix ambiguity in parsing of settings profiles: `CREATE USER ... SETTINGS profile readonly` is now considered as using a profile named `readonly`, not a setting named `profile` with the readonly constraint. This fixes [#15628](https://github.com/ClickHouse/ClickHouse/issues/15628). [#15982](https://github.com/ClickHouse/ClickHouse/pull/15982) ([Vitaly Baranov](https://github.com/vitlibar)).
- `MaterializeMySQL` (experimental feature): Fix crash on create database failure. [#15954](https://github.com/ClickHouse/ClickHouse/pull/15954) ([Winter Zhang](https://github.com/zhang2014)).
- Fixed `DROP TABLE IF EXISTS` failure with `Table ... does not exist` error when table is concurrently renamed (for Atomic database engine). Fixed rare deadlock when concurrently executing some DDL queries with multiple tables (like `DROP DATABASE` and `RENAME TABLE`) - Fixed `DROP/DETACH DATABASE` failure with `Table ... does not exist` when concurrently executing `DROP/DETACH TABLE`. [#15934](https://github.com/ClickHouse/ClickHouse/pull/15934) ([tavplubix](https://github.com/tavplubix)).
- Fix incorrect empty result for query from `Distributed` table if query has `WHERE`, `PREWHERE` and `GLOBAL IN`. Fixes [#15792](https://github.com/ClickHouse/ClickHouse/issues/15792). [#15933](https://github.com/ClickHouse/ClickHouse/pull/15933) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Fixes [#12513](https://github.com/ClickHouse/ClickHouse/issues/12513): difference expressions with same alias when query is reanalyzed. [#15886](https://github.com/ClickHouse/ClickHouse/pull/15886) ([Winter Zhang](https://github.com/zhang2014)).
- Fix possible very rare deadlocks in RBAC implementation. [#15875](https://github.com/ClickHouse/ClickHouse/pull/15875) ([Vitaly Baranov](https://github.com/vitlibar)).
- Fix exception `Block structure mismatch` in `SELECT ... ORDER BY DESC` queries which were executed after `ALTER MODIFY COLUMN` query. Fixes [#15800](https://github.com/ClickHouse/ClickHouse/issues/15800). [#15852](https://github.com/ClickHouse/ClickHouse/pull/15852) ([alesapin](https://github.com/alesapin)).
- `MaterializeMySQL` (experimental feature): Fix `select count()` inaccuracy. [#15767](https://github.com/ClickHouse/ClickHouse/pull/15767) ([tavplubix](https://github.com/tavplubix)).
- Fix some cases of queries, in which only virtual columns are selected. Previously `Not found column _nothing in block` exception may be thrown. Fixes [#12298](https://github.com/ClickHouse/ClickHouse/issues/12298). [#15756](https://github.com/ClickHouse/ClickHouse/pull/15756) ([Anton Popov](https://github.com/CurtizJ)).
- Fix drop of materialized view with inner table in Atomic database (hangs all subsequent DROP TABLE due to hang of the worker thread, due to recursive DROP TABLE for inner table of MV). [#15743](https://github.com/ClickHouse/ClickHouse/pull/15743) ([Azat Khuzhin](https://github.com/azat)).
- Possibility to move part to another disk/volume if the first attempt was failed. [#15723](https://github.com/ClickHouse/ClickHouse/pull/15723) ([Pavel Kovalenko](https://github.com/Jokser)).
- Fix error `Cannot find column` which may happen at insertion into `MATERIALIZED VIEW` in case if query for `MV` containes `ARRAY JOIN`. [#15717](https://github.com/ClickHouse/ClickHouse/pull/15717) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Fixed too low default value of `max_replicated_logs_to_keep` setting, which might cause replicas to become lost too often. Improve lost replica recovery process by choosing the most up-to-date replica to clone. Also do not remove old parts from lost replica, detach them instead. [#15701](https://github.com/ClickHouse/ClickHouse/pull/15701) ([tavplubix](https://github.com/tavplubix)).
- Fix rare race condition in dictionaries and tables from MySQL. [#15686](https://github.com/ClickHouse/ClickHouse/pull/15686) ([alesapin](https://github.com/alesapin)).
- Fix (benign) race condition in AMQP-CPP. [#15667](https://github.com/ClickHouse/ClickHouse/pull/15667) ([alesapin](https://github.com/alesapin)).
- Fix error `Cannot add simple transform to empty Pipe` which happened while reading from `Buffer` table which has different structure than destination table. It was possible if destination table returned empty result for query. Fixes [#15529](https://github.com/ClickHouse/ClickHouse/issues/15529). [#15662](https://github.com/ClickHouse/ClickHouse/pull/15662) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Proper error handling during insert into MergeTree with S3. MergeTree over S3 is an experimental feature. [#15657](https://github.com/ClickHouse/ClickHouse/pull/15657) ([Pavel Kovalenko](https://github.com/Jokser)).
- Fixed bug with S3 table function: region from URL was not applied to S3 client configuration. [#15646](https://github.com/ClickHouse/ClickHouse/pull/15646) ([Vladimir Chebotarev](https://github.com/excitoon)).