2019 Changelog

#### Improvement[​](#improvement-6 "Direct link to Improvement")

- Allow unresolvable addresses in cluster configuration. They will be considered unavailable and tried to resolve at every connection attempt. This is especially useful for Kubernetes. This fixes [#5714](https://github.com/ClickHouse/ClickHouse/issues/5714) [#5924](https://github.com/ClickHouse/ClickHouse/pull/5924) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Close idle TCP connections (with one hour timeout by default). This is especially important for large clusters with multiple distributed tables on every server, because every server can possibly keep a connection pool to every other server, and after peak query concurrency, connections will stall. This fixes [#5879](https://github.com/ClickHouse/ClickHouse/issues/5879) [#5880](https://github.com/ClickHouse/ClickHouse/pull/5880) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Better quality of `topK` function. Changed the SavingSpace set behavior to remove the last element if the new element have a bigger weight. [#5833](https://github.com/ClickHouse/ClickHouse/issues/5833) [#5850](https://github.com/ClickHouse/ClickHouse/pull/5850) ([Guillaume Tassery](https://github.com/YiuRULE))
- URL functions to work with domains now can work for incomplete URLs without scheme [#5725](https://github.com/ClickHouse/ClickHouse/pull/5725) ([alesapin](https://github.com/alesapin))
- Checksums added to the `system.parts_columns` table. [#5874](https://github.com/ClickHouse/ClickHouse/pull/5874) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov))
- Added `Enum` data type as a synonim for `Enum8` or `Enum16`. [#5886](https://github.com/ClickHouse/ClickHouse/pull/5886) ([dimarub2000](https://github.com/dimarub2000))
- Full bit transpose variant for `T64` codec. Could lead to better compression with `zstd`. [#5742](https://github.com/ClickHouse/ClickHouse/pull/5742) ([Artem Zuikov](https://github.com/4ertus2))
- Condition on `startsWith` function now can uses primary key. This fixes [#5310](https://github.com/ClickHouse/ClickHouse/issues/5310) and [#5882](https://github.com/ClickHouse/ClickHouse/issues/5882) [#5919](https://github.com/ClickHouse/ClickHouse/pull/5919) ([dimarub2000](https://github.com/dimarub2000))
- Allow to use `clickhouse-copier` with cross-replication cluster topology by permitting empty database name. [#5745](https://github.com/ClickHouse/ClickHouse/pull/5745) ([nvartolomei](https://github.com/nvartolomei))
- Use `UTC` as default timezone on a system without `tzdata` (e.g. bare Docker container). Before this patch, error message `Could not determine local time zone` was printed and server or client refused to start. [#5827](https://github.com/ClickHouse/ClickHouse/pull/5827) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Returned back support for floating point argument in function `quantileTiming` for backward compatibility. [#5911](https://github.com/ClickHouse/ClickHouse/pull/5911) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Show which table is missing column in error messages. [#5768](https://github.com/ClickHouse/ClickHouse/pull/5768) ([Ivan](https://github.com/abyss7))
- Disallow run query with same query\_id by various users [#5430](https://github.com/ClickHouse/ClickHouse/pull/5430) ([proller](https://github.com/proller))
- More robust code for sending metrics to Graphite. It will work even during long multiple `RENAME TABLE` operation. [#5875](https://github.com/ClickHouse/ClickHouse/pull/5875) ([alexey-milovidov](https://github.com/alexey-milovidov))
- More informative error messages will be displayed when ThreadPool cannot schedule a task for execution. This fixes [#5305](https://github.com/ClickHouse/ClickHouse/issues/5305) [#5801](https://github.com/ClickHouse/ClickHouse/pull/5801) ([alexey-milovidov](https://github.com/alexey-milovidov))
- Inverting ngramSearch to be more intuitive [#5807](https://github.com/ClickHouse/ClickHouse/pull/5807) ([Danila Kutenin](https://github.com/danlark1))
- Add user parsing in HDFS engine builder [#5946](https://github.com/ClickHouse/ClickHouse/pull/5946) ([akonyaev90](https://github.com/akonyaev90))
- Update default value of `max_ast_elements parameter` [#5933](https://github.com/ClickHouse/ClickHouse/pull/5933) ([Artem Konovalov](https://github.com/izebit))
- Added a notion of obsolete settings. The obsolete setting `allow_experimental_low_cardinality_type` can be used with no effect. [0f15c01c6802f7ce1a1494c12c846be8c98944cd](https://github.com/ClickHouse/ClickHouse/commit/0f15c01c6802f7ce1a1494c12c846be8c98944cd) [Alexey Milovidov](https://github.com/alexey-milovidov)

#### Performance Improvement[​](#performance-improvement-4 "Direct link to Performance Improvement")

- Increase number of streams to SELECT from Merge table for more uniform distribution of threads. Added setting `max_streams_multiplier_for_merge_tables`. This fixes [#5797](https://github.com/ClickHouse/ClickHouse/issues/5797) [#5915](https://github.com/ClickHouse/ClickHouse/pull/5915) ([alexey-milovidov](https://github.com/alexey-milovidov))

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement-7 "Direct link to Build/Testing/Packaging Improvement")