2020 Changelog

#### Improvement[​](#improvement-12 "Direct link to Improvement")

- Disallows `CODEC` on `ALIAS` column type. Fixes [#13911](https://github.com/ClickHouse/ClickHouse/issues/13911). [#14263](https://github.com/ClickHouse/ClickHouse/pull/14263) ([Bharat Nallan](https://github.com/bharatnc)).
- When waiting for a dictionary update to complete, use the timeout specified by `query_wait_timeout_milliseconds` setting instead of a hard-coded value. [#14105](https://github.com/ClickHouse/ClickHouse/pull/14105) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Add setting `min_index_granularity_bytes` that protects against accidentally creating a table with very low `index_granularity_bytes` setting. [#14139](https://github.com/ClickHouse/ClickHouse/pull/14139) ([Bharat Nallan](https://github.com/bharatnc)).
- Now it's possible to fetch partitions from clusters that use different ZooKeeper: `ALTER TABLE table_name FETCH PARTITION partition_expr FROM 'zk-name:/path-in-zookeeper'`. It's useful for shipping data to new clusters. [#14155](https://github.com/ClickHouse/ClickHouse/pull/14155) ([Amos Bird](https://github.com/amosbird)).
- Slightly better performance of Memory table if it was constructed from a huge number of very small blocks (that's unlikely). Author of the idea: [Mark Papadakis](https://github.com/markpapadakis). Closes [#14043](https://github.com/ClickHouse/ClickHouse/issues/14043). [#14056](https://github.com/ClickHouse/ClickHouse/pull/14056) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Conditional aggregate functions (for example: `avgIf`, `sumIf`, `maxIf`) should return `NULL` when miss rows and use nullable arguments. [#13964](https://github.com/ClickHouse/ClickHouse/pull/13964) ([Winter Zhang](https://github.com/zhang2014)).
- Increase limit in -Resample combinator to 1M. [#13947](https://github.com/ClickHouse/ClickHouse/pull/13947) ([Mikhail f. Shiryaev](https://github.com/Felixoid)).
- Corrected an error in AvroConfluent format that caused the Kafka table engine to stop processing messages when an abnormally small, malformed, message was received. [#13941](https://github.com/ClickHouse/ClickHouse/pull/13941) ([Gervasio Varela](https://github.com/gervarela)).
- Fix wrong error for long queries. It was possible to get syntax error other than `Max query size exceeded` for correct query. [#13928](https://github.com/ClickHouse/ClickHouse/pull/13928) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Better error message for null value of `TabSeparated` format. [#13906](https://github.com/ClickHouse/ClickHouse/pull/13906) ([jiang tao](https://github.com/tomjiang1987)).
- Function `arrayCompact` will compare NaNs bitwise if the type of array elements is Float32/Float64. In previous versions NaNs were always not equal if the type of array elements is Float32/Float64 and were always equal if the type is more complex, like Nullable(Float64). This closes [#13857](https://github.com/ClickHouse/ClickHouse/issues/13857). [#13868](https://github.com/ClickHouse/ClickHouse/pull/13868) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix data race in `lgamma` function. This race was caught only in `tsan`, no side effects a really happened. [#13842](https://github.com/ClickHouse/ClickHouse/pull/13842) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Avoid too slow queries when arrays are manipulated as fields. Throw exception instead. [#13753](https://github.com/ClickHouse/ClickHouse/pull/13753) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Added Redis requirepass authorization (for redis dictionary source). [#13688](https://github.com/ClickHouse/ClickHouse/pull/13688) ([Ivan Torgashov](https://github.com/it1804)).
- Add MergeTree Write-Ahead-Log (WAL) dump tool. WAL is an experimental feature. [#13640](https://github.com/ClickHouse/ClickHouse/pull/13640) ([BohuTANG](https://github.com/BohuTANG)).
- In previous versions `lcm` function may produce assertion violation in debug build if called with specifically crafted arguments. This fixes [#13368](https://github.com/ClickHouse/ClickHouse/issues/13368). [#13510](https://github.com/ClickHouse/ClickHouse/pull/13510) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Provide monotonicity for `toDate/toDateTime` functions in more cases. Monotonicity information is used for index analysis (more complex queries will be able to use index). Now the input arguments are saturated more naturally and provides better monotonicity. [#13497](https://github.com/ClickHouse/ClickHouse/pull/13497) ([Amos Bird](https://github.com/amosbird)).
- Support compound identifiers for custom settings. Custom settings is an integration point of ClickHouse codebase with other codebases (no benefits for ClickHouse itself) [#13496](https://github.com/ClickHouse/ClickHouse/pull/13496) ([Vitaly Baranov](https://github.com/vitlibar)).
- Move parts from DiskLocal to DiskS3 in parallel. `DiskS3` is an experimental feature. [#13459](https://github.com/ClickHouse/ClickHouse/pull/13459) ([Pavel Kovalenko](https://github.com/Jokser)).
- Enable mixed granularity parts by default. [#13449](https://github.com/ClickHouse/ClickHouse/pull/13449) ([alesapin](https://github.com/alesapin)).
- Proper remote host checking in S3 redirects (security-related thing). [#13404](https://github.com/ClickHouse/ClickHouse/pull/13404) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Add `QueryTimeMicroseconds`, `SelectQueryTimeMicroseconds` and `InsertQueryTimeMicroseconds` to system.events. [#13336](https://github.com/ClickHouse/ClickHouse/pull/13336) ([ianton-ru](https://github.com/ianton-ru)).
- Fix debug assertion when Decimal has too large negative exponent. Fixes [#13188](https://github.com/ClickHouse/ClickHouse/issues/13188). [#13228](https://github.com/ClickHouse/ClickHouse/pull/13228) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Added cache layer for DiskS3 (cache to local disk mark and index files). `DiskS3` is an experimental feature. [#13076](https://github.com/ClickHouse/ClickHouse/pull/13076) ([Pavel Kovalenko](https://github.com/Jokser)).
- Fix readline so it dumps history to file now. [#13600](https://github.com/ClickHouse/ClickHouse/pull/13600) ([Amos Bird](https://github.com/amosbird)).
- Create `system` database with `Atomic` engine by default (a preparation to enable `Atomic` database engine by default everywhere). [#13680](https://github.com/ClickHouse/ClickHouse/pull/13680) ([tavplubix](https://github.com/tavplubix)).

#### Performance Improvement[​](#performance-improvement-5 "Direct link to Performance Improvement")