2020 Changelog

#### Improvement[​](#improvement-10 "Direct link to Improvement")

- Now it's possible to change the type of version column for `VersionedCollapsingMergeTree` with `ALTER` query. [#15442](https://github.com/ClickHouse/ClickHouse/pull/15442) ([alesapin](https://github.com/alesapin)).

### ClickHouse release v20.8.3.18-stable, 2020-09-18[​](#clickhouse-release-v208318-stable-2020-09-18 "Direct link to ClickHouse release v20.8.3.18-stable, 2020-09-18")

#### Bug Fix[​](#bug-fix-22 "Direct link to Bug Fix")

- Fix the issue when some invocations of `extractAllGroups` function may trigger "Memory limit exceeded" error. This fixes [#13383](https://github.com/ClickHouse/ClickHouse/issues/13383). [#14889](https://github.com/ClickHouse/ClickHouse/pull/14889) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Fix SIGSEGV for an attempt to INSERT into StorageFile(fd). [#14887](https://github.com/ClickHouse/ClickHouse/pull/14887) ([Azat Khuzhin](https://github.com/azat)).
- Fix rare error in `SELECT` queries when the queried column has `DEFAULT` expression which depends on the other column which also has `DEFAULT` and not present in select query and not exists on disk. Partially fixes [#14531](https://github.com/ClickHouse/ClickHouse/issues/14531). [#14845](https://github.com/ClickHouse/ClickHouse/pull/14845) ([alesapin](https://github.com/alesapin)).
- Fixed missed default database name in metadata of materialized view when executing `ALTER ... MODIFY QUERY`. [#14664](https://github.com/ClickHouse/ClickHouse/pull/14664) ([tavplubix](https://github.com/tavplubix)).
- Fix bug when `ALTER UPDATE` mutation with Nullable column in assignment expression and constant value (like `UPDATE x = 42`) leads to incorrect value in column or segfault. Fixes [#13634](https://github.com/ClickHouse/ClickHouse/issues/13634), [#14045](https://github.com/ClickHouse/ClickHouse/issues/14045). [#14646](https://github.com/ClickHouse/ClickHouse/pull/14646) ([alesapin](https://github.com/alesapin)).
- Fix wrong Decimal multiplication result caused wrong decimal scale of result column. [#14603](https://github.com/ClickHouse/ClickHouse/pull/14603) ([Artem Zuikov](https://github.com/4ertus2)).
- Added the checker as neither calling `lc->isNullable()` nor calling `ls->getDictionaryPtr()->isNullable()` would return the correct result. [#14591](https://github.com/ClickHouse/ClickHouse/pull/14591) ([myrrc](https://github.com/myrrc)).
- Cleanup data directory after Zookeeper exceptions during CreateQuery for StorageReplicatedMergeTree Engine. [#14563](https://github.com/ClickHouse/ClickHouse/pull/14563) ([Bharat Nallan](https://github.com/bharatnc)).
- Fix rare segfaults in functions with combinator -Resample, which could appear in result of overflow with very large parameters. [#14562](https://github.com/ClickHouse/ClickHouse/pull/14562) ([Anton Popov](https://github.com/CurtizJ)).

#### Improvement[​](#improvement-11 "Direct link to Improvement")

- Speed up server shutdown process if there are ongoing S3 requests. [#14858](https://github.com/ClickHouse/ClickHouse/pull/14858) ([Pavel Kovalenko](https://github.com/Jokser)).
- Allow using multi-volume storage configuration in storage Distributed. [#14839](https://github.com/ClickHouse/ClickHouse/pull/14839) ([Pavel Kovalenko](https://github.com/Jokser)).
- Speed up server shutdown process if there are ongoing S3 requests. [#14496](https://github.com/ClickHouse/ClickHouse/pull/14496) ([Pavel Kovalenko](https://github.com/Jokser)).
- Support custom codecs in compact parts. [#12183](https://github.com/ClickHouse/ClickHouse/pull/12183) ([Anton Popov](https://github.com/CurtizJ)).

### ClickHouse release v20.8.2.3-stable, 2020-09-08[​](#clickhouse-release-v20823-stable-2020-09-08 "Direct link to ClickHouse release v20.8.2.3-stable, 2020-09-08")

#### Backward Incompatible Change[​](#backward-incompatible-change-4 "Direct link to Backward Incompatible Change")

- Now `OPTIMIZE FINAL` query does not recalculate TTL for parts that were added before TTL was created. Use `ALTER TABLE ... MATERIALIZE TTL` once to calculate them, after that `OPTIMIZE FINAL` will evaluate TTL's properly. This behavior never worked for replicated tables. [#14220](https://github.com/ClickHouse/ClickHouse/pull/14220) ([alesapin](https://github.com/alesapin)).
- Extend `parallel_distributed_insert_select` setting, adding an option to run `INSERT` into local table. The setting changes type from `Bool` to `UInt64`, so the values `false` and `true` are no longer supported. If you have these values in server configuration, the server will not start. Please replace them with `0` and `1`, respectively. [#14060](https://github.com/ClickHouse/ClickHouse/pull/14060) ([Azat Khuzhin](https://github.com/azat)).
- Remove support for the `ODBCDriver` input/output format. This was a deprecated format once used for communication with the ClickHouse ODBC driver, now long superseded by the `ODBCDriver2` format. Resolves [#13629](https://github.com/ClickHouse/ClickHouse/issues/13629). [#13847](https://github.com/ClickHouse/ClickHouse/pull/13847) ([hexiaoting](https://github.com/hexiaoting)).
- 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-4 "Direct link to New Feature")