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Update changelog to include caveats about Nullable types in data skipping indexes

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Azat Khuzhin 2021-10-07 21:02:38 +03:00
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CHANGELOG.md
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@ -110,6 +110,7 @@
* Fix the issue that in case of some sophisticated query with column aliases identical to the names of expressions, bad cast may happen. This fixes [#25447](https://github.com/ClickHouse/ClickHouse/issues/25447). This fixes [#26914](https://github.com/ClickHouse/ClickHouse/issues/26914). This fix may introduce backward incompatibility: if there are different expressions with identical names, exception will be thrown. It may break some rare cases when `enable_optimize_predicate_expression` is set. [#26639](https://github.com/ClickHouse/ClickHouse/pull/26639) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Now, scalar subquery always returns `Nullable` result if it's type can be `Nullable`. It is needed because in case of empty subquery it's result should be `Null`. Previously, it was possible to get error about incompatible types (type deduction does not execute scalar subquery, and it could use not-nullable type). Scalar subquery with empty result which can't be converted to `Nullable` (like `Array` or `Tuple`) now throws error. Fixes [#25411](https://github.com/ClickHouse/ClickHouse/issues/25411). [#26423](https://github.com/ClickHouse/ClickHouse/pull/26423) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Introduce syntax for here documents. Example `SELECT $doc$ VALUE $doc$`. [#26671](https://github.com/ClickHouse/ClickHouse/pull/26671) ([Maksim Kita](https://github.com/kitaisreal)). This change is backward incompatible if in query there are identifiers that contain `$` [#28768](https://github.com/ClickHouse/ClickHouse/issues/28768).
* Now indices can handle Nullable types, including `isNull` and `isNotNull`. [#12433](https://github.com/ClickHouse/ClickHouse/pull/12433) and [#12455](https://github.com/ClickHouse/ClickHouse/pull/12455) ([Amos Bird](https://github.com/amosbird)) and [#27250](https://github.com/ClickHouse/ClickHouse/pull/27250) ([Azat Khuzhin](https://github.com/azat)). But this was done with on-disk format changes, and even though new server can read old data, old server cannot. Also, in case you have `MINMAX` data skipping indices, you may get `Data after mutation/merge is not byte-identical` error, since new index will have `.idx2` extension while before it was `.idx`. That said, that you should not delay updating all existing replicas, in this case, otherwise, if old replica (<21.9) will download data from new replica with 21.9+ it will not be able to apply index for downloaded part.
#### New Feature
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* Add setting `log_formatted_queries` to log additional formatted query into `system.query_log`. It's useful for normalized query analysis because functions like `normalizeQuery` and `normalizeQueryKeepNames` don't parse/format queries in order to achieve better performance. [#27380](https://github.com/ClickHouse/ClickHouse/pull/27380) ([Amos Bird](https://github.com/amosbird)).
* Add two settings `max_hyperscan_regexp_length` and `max_hyperscan_regexp_total_length` to prevent huge regexp being used in hyperscan related functions, such as `multiMatchAny`. [#27378](https://github.com/ClickHouse/ClickHouse/pull/27378) ([Amos Bird](https://github.com/amosbird)).
* Memory consumed by bitmap aggregate functions now is taken into account for memory limits. This closes [#26555](https://github.com/ClickHouse/ClickHouse/issues/26555). [#27252](https://github.com/ClickHouse/ClickHouse/pull/27252) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add new index data skipping minmax index format for proper Nullable support. [#27250](https://github.com/ClickHouse/ClickHouse/pull/27250) ([Azat Khuzhin](https://github.com/azat)).
* Add 10 seconds cache for S3 proxy resolver. [#27216](https://github.com/ClickHouse/ClickHouse/pull/27216) ([ianton-ru](https://github.com/ianton-ru)).
* Split global mutex into individual regexp construction. This helps avoid huge regexp construction blocking other related threads. [#27211](https://github.com/ClickHouse/ClickHouse/pull/27211) ([Amos Bird](https://github.com/amosbird)).
* Support schema for PostgreSQL database engine. Closes [#27166](https://github.com/ClickHouse/ClickHouse/issues/27166). [#27198](https://github.com/ClickHouse/ClickHouse/pull/27198) ([Kseniia Sumarokova](https://github.com/kssenii)).
@ -234,7 +234,6 @@
* Fix multiple block insertion into distributed table with `insert_distributed_one_random_shard = 1`. This is a marginal feature. Mark as improvement. [#23140](https://github.com/ClickHouse/ClickHouse/pull/23140) ([Amos Bird](https://github.com/amosbird)).
* Support `LowCardinality` and `FixedString` keys/values for `Map` type. [#21543](https://github.com/ClickHouse/ClickHouse/pull/21543) ([hexiaoting](https://github.com/hexiaoting)).
* Enable reloading of local disk config. [#19526](https://github.com/ClickHouse/ClickHouse/pull/19526) ([taiyang-li](https://github.com/taiyang-li)).
* Now KeyConditions can correctly skip nullable keys, including `isNull` and `isNotNull`. https://github.com/ClickHouse/ClickHouse/pull/12433. [#12455](https://github.com/ClickHouse/ClickHouse/pull/12455) ([Amos Bird](https://github.com/amosbird)).
#### Bug Fix