ClickHouse/clickhouse-docs-embeddings huggingface dataset:
2023 Changelog

### ClickHouse release 23.8 LTS, 2023-08-31. [Presentation](https://presentations.clickhouse.com/2023-release-23.8/), [Video](https://www.youtube.com/watch?v=d1_pyoWcydk)[​](#238 "Direct link to 238")

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

- If a dynamic disk contains a name, it should be specified as `disk = disk(name = 'disk_name'`, ...) in disk function arguments. In previous version it could be specified as `disk = disk_<disk_name>(...)`, which is no longer supported. [#52820](https://github.com/ClickHouse/ClickHouse/pull/52820) ([Kseniia Sumarokova](https://github.com/kssenii)).
- `clickhouse-benchmark` will establish connections in parallel when invoked with `--concurrency` more than one. Previously it was unusable if you ran it with 1000 concurrent connections from Europe to the US. Correct calculation of QPS for connections with high latency. Backward incompatible change: the option for JSON output of `clickhouse-benchmark` is removed. If you've used this option, you can also extract data from the `system.query_log` in JSON format as a workaround. [#53293](https://github.com/ClickHouse/ClickHouse/pull/53293) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- The `microseconds` column is removed from the `system.text_log`, and the `milliseconds` column is removed from the `system.metric_log`, because they are redundant in the presence of the `event_time_microseconds` column. [#53601](https://github.com/ClickHouse/ClickHouse/pull/53601) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Deprecate the metadata cache feature. It is experimental and we have never used it. The feature is dangerous: [#51182](https://github.com/ClickHouse/ClickHouse/issues/51182). Remove the `system.merge_tree_metadata_cache` system table. The metadata cache is still available in this version but will be removed soon. This closes [#39197](https://github.com/ClickHouse/ClickHouse/issues/39197). [#51303](https://github.com/ClickHouse/ClickHouse/pull/51303) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Disable support for 3DES in TLS connections. [#52893](https://github.com/ClickHouse/ClickHouse/pull/52893) ([Kenji Noguchi](https://github.com/knoguchi)).

#### New Feature[​](#new-feature-4 "Direct link to New Feature")
2023 Changelog

### ClickHouse release 23.7, 2023-07-27. [Presentation](https://presentations.clickhouse.com/2023-release-23.7/), [Video](https://www.youtube.com/watch?v=TI1kONfON18)[​](#237 "Direct link to 237")

#### Backward Incompatible Change[​](#backward-incompatible-change-5 "Direct link to Backward Incompatible Change")

- Add `NAMED COLLECTION` access type (aliases `USE NAMED COLLECTION`, `NAMED COLLECTION USAGE`). This PR is backward incompatible because this access type is disabled by default (because a parent access type `NAMED COLLECTION ADMIN` is disabled by default as well). Proposed in [#50277](https://github.com/ClickHouse/ClickHouse/issues/50277). To grant use `GRANT NAMED COLLECTION ON collection_name TO user` or `GRANT NAMED COLLECTION ON * TO user`, to be able to give these grants `named_collection_admin` is required in config (previously it was named `named_collection_control`, so will remain as an alias). [#50625](https://github.com/ClickHouse/ClickHouse/pull/50625) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Fixing a typo in the `system.parts` column name `last_removal_attemp_time`. Now it is named `last_removal_attempt_time`. [#52104](https://github.com/ClickHouse/ClickHouse/pull/52104) ([filimonov](https://github.com/filimonov)).
- Bump version of the distributed\_ddl\_entry\_format\_version to 5 by default (enables opentelemetry and initial\_query\_idd pass through). This will not allow to process existing entries for distributed DDL after *downgrade* (but note, that usually there should be no such unprocessed entries). [#52128](https://github.com/ClickHouse/ClickHouse/pull/52128) ([Azat Khuzhin](https://github.com/azat)).
- Check projection metadata the same way we check ordinary metadata. This change may prevent the server from starting in case there was a table with an invalid projection. An example is a projection that created positional columns in PK (e.g. `projection p (select * order by 1, 4)` which is not allowed in table PK and can cause a crash during insert/merge). Drop such projections before the update. Fixes [#52353](https://github.com/ClickHouse/ClickHouse/issues/52353). [#52361](https://github.com/ClickHouse/ClickHouse/pull/52361) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- The experimental feature `hashid` is removed due to a bug. The quality of implementation was questionable at the start, and it didn't get through the experimental status. This closes [#52406](https://github.com/ClickHouse/ClickHouse/issues/52406). [#52449](https://github.com/ClickHouse/ClickHouse/pull/52449) ([Alexey Milovidov](https://github.com/alexey-milovidov)).

#### New Feature[​](#new-feature-5 "Direct link to New Feature")
2023 Changelog

- In cases where the HTTP endpoint has multiple IP addresses and the first of them is unreachable, a timeout exception was thrown. Made session creation with handling all resolved endpoints. [#52116](https://github.com/ClickHouse/ClickHouse/pull/52116) ([Aleksei Filatov](https://github.com/aalexfvk)).
- Avro input format now supports Union even if it contains only a single type. Closes [#52131](https://github.com/ClickHouse/ClickHouse/issues/52131). [#52137](https://github.com/ClickHouse/ClickHouse/pull/52137) ([flynn](https://github.com/ucasfl)).
- Add setting `optimize_use_implicit_projections` to disable implicit projections (currently only `min_max_count` projection). [#52152](https://github.com/ClickHouse/ClickHouse/pull/52152) ([Amos Bird](https://github.com/amosbird)).
- It was possible to use the function `hasToken` for infinite loop. Now this possibility is removed. This closes [#52156](https://github.com/ClickHouse/ClickHouse/issues/52156). [#52160](https://github.com/ClickHouse/ClickHouse/pull/52160) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Create ZK ancestors optimistically. [#52195](https://github.com/ClickHouse/ClickHouse/pull/52195) ([Raúl Marín](https://github.com/Algunenano)).
- Fix [#50582](https://github.com/ClickHouse/ClickHouse/issues/50582). Avoid the `Not found column ... in block` error in some cases of reading in-order and constants. [#52259](https://github.com/ClickHouse/ClickHouse/pull/52259) ([Chen768959](https://github.com/Chen768959)).
- Check whether S2 geo primitives are invalid as early as possible on ClickHouse side. This closes: [#27090](https://github.com/ClickHouse/ClickHouse/issues/27090). [#52260](https://github.com/ClickHouse/ClickHouse/pull/52260) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Add back missing projection QueryAccessInfo when `query_plan_optimize_projection = 1`. This fixes [#50183](https://github.com/ClickHouse/ClickHouse/issues/50183) . This fixes [#50093](https://github.com/ClickHouse/ClickHouse/issues/50093). [#52327](https://github.com/ClickHouse/ClickHouse/pull/52327) ([Amos Bird](https://github.com/amosbird)).
- When `ZooKeeperRetriesControl` rethrows an error, it's more useful to see its original stack trace, not the one from `ZooKeeperRetriesControl` itself. [#52347](https://github.com/ClickHouse/ClickHouse/pull/52347) ([Vitaly Baranov](https://github.com/vitlibar)).
- Wait for zero copy replication lock even if some disks don't support it. [#52376](https://github.com/ClickHouse/ClickHouse/pull/52376) ([Raúl Marín](https://github.com/Algunenano)).
- Now interserver port will be closed only after tables are shut down. [#52498](https://github.com/ClickHouse/ClickHouse/pull/52498) ([alesapin](https://github.com/alesapin)).
2023 Changelog

- Added `toLastDayOfWeek` function to round a date or a date with time up to the nearest Saturday or Sunday. [#50315](https://github.com/ClickHouse/ClickHouse/pull/50315) ([Victor Krasnov](https://github.com/sirvickr)).
- Ability to ignore a skip index by specifying `ignore_data_skipping_indices`. [#50329](https://github.com/ClickHouse/ClickHouse/pull/50329) ([Boris Kuschel](https://github.com/bkuschel)).
- Add `system.user_processes` table and `SHOW USER PROCESSES` query to show memory info and ProfileEvents on user level. [#50492](https://github.com/ClickHouse/ClickHouse/pull/50492) ([János Benjamin Antal](https://github.com/antaljanosbenjamin)).
- Add server and format settings `display_secrets_in_show_and_select` for displaying secrets of tables, databases, table functions, and dictionaries. Add privilege `displaySecretsInShowAndSelect` controlling which users can view secrets. [#46528](https://github.com/ClickHouse/ClickHouse/pull/46528) ([Mike Kot](https://github.com/myrrc)).
- Allow to set up a ROW POLICY for all tables that belong to a DATABASE. [#47640](https://github.com/ClickHouse/ClickHouse/pull/47640) ([Ilya Golshtein](https://github.com/ilejn)).
2023 Changelog

#### Experimental Feature[​](#experimental-feature-4 "Direct link to Experimental Feature")

- `DEFLATE_QPL` codec lower the minimum simd version to SSE 4.2. [doc change in qpl](https://github.com/intel/qpl/commit/3f8f5cea27739f5261e8fd577dc233ffe88bf679) - Intel® QPL relies on a run-time kernels dispatcher and cpuid check to choose the best available implementation(sse/avx2/avx512) - restructured cmakefile for qpl build in clickhouse to align with latest upstream qpl. [#49811](https://github.com/ClickHouse/ClickHouse/pull/49811) ([jasperzhu](https://github.com/jinjunzh)).
- Add initial support to do JOINs with pure parallel replicas. [#49544](https://github.com/ClickHouse/ClickHouse/pull/49544) ([Raúl Marín](https://github.com/Algunenano)).
- More parallelism on `Outdated` parts removal with "zero-copy replication". [#49630](https://github.com/ClickHouse/ClickHouse/pull/49630) ([Alexander Tokmakov](https://github.com/tavplubix)).
- Parallel Replicas: 1) Fixed an error `NOT_FOUND_COLUMN_IN_BLOCK` in case of using parallel replicas with non-replicated storage with disabled setting `parallel_replicas_for_non_replicated_merge_tree` 2) Now `allow_experimental_parallel_reading_from_replicas` have 3 possible values - 0, 1 and 2. 0 - disabled, 1 - enabled, silently disable them in case of failure (in case of FINAL or JOIN), 2 - enabled, throw an exception in case of failure. 3) If FINAL modifier is used in SELECT query and parallel replicas are enabled, ClickHouse will try to disable them if `allow_experimental_parallel_reading_from_replicas` is set to 1 and throw an exception otherwise. [#50195](https://github.com/ClickHouse/ClickHouse/pull/50195) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- When parallel replicas are enabled they will always skip unavailable servers (the behavior is controlled by the setting `skip_unavailable_shards`, enabled by default and can be only disabled). This closes: [#48565](https://github.com/ClickHouse/ClickHouse/issues/48565). [#50293](https://github.com/ClickHouse/ClickHouse/pull/50293) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).

#### Improvement[​](#improvement-7 "Direct link to Improvement")
2023 Changelog

- Preserve initial\_query\_id for ON CLUSTER queries, which is useful for introspection (under `distributed_ddl_entry_format_version=5`). [#50015](https://github.com/ClickHouse/ClickHouse/pull/50015) ([Azat Khuzhin](https://github.com/azat)).
- Preserve backward incompatibility for renamed settings by using aliases (`allow_experimental_projection_optimization` for `optimize_use_projections`, `allow_experimental_lightweight_delete` for `enable_lightweight_delete`). [#50044](https://github.com/ClickHouse/ClickHouse/pull/50044) ([Azat Khuzhin](https://github.com/azat)).
- Support passing FQDN through setting my\_hostname to register cluster node in keeper. Add setting of invisible to support multi compute groups. A compute group as a cluster, is invisible to other compute groups. [#50186](https://github.com/ClickHouse/ClickHouse/pull/50186) ([Yangkuan Liu](https://github.com/LiuYangkuan)).
- Fix PostgreSQL reading all the data even though `LIMIT n` could be specified. [#50187](https://github.com/ClickHouse/ClickHouse/pull/50187) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add new profile events for queries with subqueries (`QueriesWithSubqueries`/`SelectQueriesWithSubqueries`/`InsertQueriesWithSubqueries`). [#50204](https://github.com/ClickHouse/ClickHouse/pull/50204) ([Azat Khuzhin](https://github.com/azat)).
- Adding the roles field in the users.xml file, which allows specifying roles with grants via a config file. [#50278](https://github.com/ClickHouse/ClickHouse/pull/50278) ([pufit](https://github.com/pufit)).
- Report `CGroupCpuCfsPeriod` and `CGroupCpuCfsQuota` in AsynchronousMetrics. - Respect cgroup v2 memory limits during server startup. [#50379](https://github.com/ClickHouse/ClickHouse/pull/50379) ([alekar](https://github.com/alekar)).
- Add a signal handler for SIGQUIT to work the same way as SIGINT. Closes [#50298](https://github.com/ClickHouse/ClickHouse/issues/50298). [#50435](https://github.com/ClickHouse/ClickHouse/pull/50435) ([Nikolay Degterinsky](https://github.com/evillique)).
- In case JSON parse fails due to the large size of the object output the last position to allow debugging. [#50474](https://github.com/ClickHouse/ClickHouse/pull/50474) ([Valentin Alexeev](https://github.com/valentinalexeev)).
- Support decimals with not fixed size. Closes [#49130](https://github.com/ClickHouse/ClickHouse/issues/49130). [#50586](https://github.com/ClickHouse/ClickHouse/pull/50586) ([Kruglov Pavel](https://github.com/Avogar)).
2023 Changelog

- Improve the embedded dashboard. Close [#46671](https://github.com/ClickHouse/ClickHouse/issues/46671). [#49036](https://github.com/ClickHouse/ClickHouse/pull/49036) ([Kevin Zhang](https://github.com/Kinzeng)).
- Add profile events for log messages, so you can easily see the count of log messages by severity. [#49042](https://github.com/ClickHouse/ClickHouse/pull/49042) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- In previous versions, the `LineAsString` format worked inconsistently when the parallel parsing was enabled or not, in presence of DOS or macOS Classic line breaks. This closes [#49039](https://github.com/ClickHouse/ClickHouse/issues/49039). [#49052](https://github.com/ClickHouse/ClickHouse/pull/49052) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- The exception message about the unparsed query parameter will also tell about the name of the parameter. Reimplement [#48878](https://github.com/ClickHouse/ClickHouse/issues/48878). Close [#48772](https://github.com/ClickHouse/ClickHouse/issues/48772). [#49061](https://github.com/ClickHouse/ClickHouse/pull/49061) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
2023 Changelog

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement-8 "Direct link to Build/Testing/Packaging Improvement")

- Update time zones. The following were updated: Africa/Cairo, Africa/Casablanca, Africa/El\_Aaiun, America/Bogota, America/Cambridge\_Bay, America/Ciudad\_Juarez, America/Godthab, America/Inuvik, America/Iqaluit, America/Nuuk, America/Ojinaga, America/Pangnirtung, America/Rankin\_Inlet, America/Resolute, America/Whitehorse, America/Yellowknife, Asia/Gaza, Asia/Hebron, Asia/Kuala\_Lumpur, Asia/Singapore, Canada/Yukon, Egypt, Europe/Kirov, Europe/Volgograd, Singapore. [#48572](https://github.com/ClickHouse/ClickHouse/pull/48572) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Reduce the number of dependencies in the header files to speed up the build. [#47984](https://github.com/ClickHouse/ClickHouse/pull/47984) ([Dmitry Novik](https://github.com/novikd)).
- Randomize compression of marks and indices in tests. [#48286](https://github.com/ClickHouse/ClickHouse/pull/48286) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Bump internal ZSTD from 1.5.4 to 1.5.5. [#46797](https://github.com/ClickHouse/ClickHouse/pull/46797) ([Robert Schulze](https://github.com/rschu1ze)).
- Randomize vertical merges from compact to wide parts in tests. [#48287](https://github.com/ClickHouse/ClickHouse/pull/48287) ([Raúl Marín](https://github.com/Algunenano)).
- Support for CRC32 checksum in HDFS. Fix performance issues. [#48614](https://github.com/ClickHouse/ClickHouse/pull/48614) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Remove remainders of GCC support. [#48671](https://github.com/ClickHouse/ClickHouse/pull/48671) ([Robert Schulze](https://github.com/rschu1ze)).
- Add CI run with new analyzer infrastructure enabled. [#48719](https://github.com/ClickHouse/ClickHouse/pull/48719) ([Dmitry Novik](https://github.com/novikd)).

#### Bug Fix (user-visible misbehavior in an official stable release)[​](#bug-fix-user-visible-misbehavior-in-an-official-stable-release-8 "Direct link to Bug Fix (user-visible misbehavior in an official stable release)")
2023 Changelog

### ClickHouse release 23.3 LTS, 2023-03-30. [Presentation](https://presentations.clickhouse.com/2023-release-23.3/), [Video](https://www.youtube.com/watch?v=ISaGUjvBNao)[​](#233 "Direct link to 233")

#### Upgrade Notes[​](#upgrade-notes-1 "Direct link to Upgrade Notes")

- Lightweight DELETEs are production ready and enabled by default. The `DELETE` query for MergeTree tables is now available by default.
- The behavior of `*domain*RFC` and `netloc` functions is slightly changed: relaxed the set of symbols that are allowed in the URL authority for better conformance. [#46841](https://github.com/ClickHouse/ClickHouse/pull/46841) ([Azat Khuzhin](https://github.com/azat)).
- Prohibited creating tables based on KafkaEngine with DEFAULT/EPHEMERAL/ALIAS/MATERIALIZED statements for columns. [#47138](https://github.com/ClickHouse/ClickHouse/pull/47138) ([Aleksandr Musorin](https://github.com/AVMusorin)).
- An "asynchronous connection drain" feature is removed. Related settings and metrics are removed as well. It was an internal feature, so the removal should not affect users who had never heard about that feature. [#47486](https://github.com/ClickHouse/ClickHouse/pull/47486) ([Alexander Tokmakov](https://github.com/tavplubix)).
- Support 256-bit Decimal data type (more than 38 digits) in `arraySum`/`Min`/`Max`/`Avg`/`Product`, `arrayCumSum`/`CumSumNonNegative`, `arrayDifference`, array construction, IN operator, query parameters, `groupArrayMovingSum`, statistical functions, `min`/`max`/`any`/`argMin`/`argMax`, PostgreSQL wire protocol, MySQL table engine and function, `sumMap`, `mapAdd`, `mapSubtract`, `arrayIntersect`. Add support for big integers in `arrayIntersect`. Statistical aggregate functions involving moments (such as `corr` or various `TTest`s) will use `Float64` as their internal representation (they were using `Decimal128` before this change, but it was pointless), and these functions can return `nan` instead of `inf` in case of infinite variance. Some functions were allowed on `Decimal256` data types but returned `Decimal128` in previous versions - now it is fixed. This closes [#47569](https://github.com/ClickHouse/ClickHouse/issues/47569). This closes [#44864](https://github.com/ClickHouse/ClickHouse/issues/44864). This closes [#28335](https://github.com/ClickHouse/ClickHouse/issues/28335). [#47594](https://github.com/ClickHouse/ClickHouse/pull/47594) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Make backup\_threads/restore\_threads server settings (instead of user settings). [#47881](https://github.com/ClickHouse/ClickHouse/pull/47881) ([Azat Khuzhin](https://github.com/azat)).
- Do not allow const and non-deterministic secondary indices [#46839](https://github.com/ClickHouse/ClickHouse/pull/46839) ([Anton Popov](https://github.com/CurtizJ)).

#### New Feature[​](#new-feature-9 "Direct link to New Feature")
2023 Changelog

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement-9 "Direct link to Build/Testing/Packaging Improvement")

- ClickHouse now builds with `C++23`. [#47424](https://github.com/ClickHouse/ClickHouse/pull/47424) ([Robert Schulze](https://github.com/rschu1ze)).
- Fuzz `EXPLAIN` queries in the AST Fuzzer. [#47803](https://github.com/ClickHouse/ClickHouse/pull/47803) [#47852](https://github.com/ClickHouse/ClickHouse/pull/47852) ([flynn](https://github.com/ucasfl)).
- Split stress test and the automated backward compatibility check (now Upgrade check). [#44879](https://github.com/ClickHouse/ClickHouse/pull/44879) ([Kruglov Pavel](https://github.com/Avogar)).
- Updated the Ubuntu Image for Docker to calm down some bogus security reports. [#46784](https://github.com/ClickHouse/ClickHouse/pull/46784) ([Julio Jimenez](https://github.com/juliojimenez)). Please note that ClickHouse has no dependencies and does not require Docker.
- Adds a prompt to allow the removal of an existing `clickhouse` download when using "curl | sh" download of ClickHouse. Prompt is "ClickHouse binary clickhouse already exists. Overwrite? [y/N]". [#46859](https://github.com/ClickHouse/ClickHouse/pull/46859) ([Dan Roscigno](https://github.com/DanRoscigno)).
- Fix error during server startup on old distros (e.g. Amazon Linux 2) and on ARM that glibc 2.28 symbols are not found. [#47008](https://github.com/ClickHouse/ClickHouse/pull/47008) ([Robert Schulze](https://github.com/rschu1ze)).
- Prepare for clang 16. [#47027](https://github.com/ClickHouse/ClickHouse/pull/47027) ([Amos Bird](https://github.com/amosbird)).
- Added a CI check which ensures ClickHouse can run with an old glibc on ARM. [#47063](https://github.com/ClickHouse/ClickHouse/pull/47063) ([Robert Schulze](https://github.com/rschu1ze)).
- Add a style check to prevent incorrect usage of the `NDEBUG` macro. [#47699](https://github.com/ClickHouse/ClickHouse/pull/47699) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Speed up the build a little. [#47714](https://github.com/ClickHouse/ClickHouse/pull/47714) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Bump `vectorscan` to 5.4.9. [#47955](https://github.com/ClickHouse/ClickHouse/pull/47955) ([Robert Schulze](https://github.com/rschu1ze)).
- Add a unit test to assert Apache Arrow's fatal logging does not abort. It covers the changes in [ClickHouse/arrow#16](https://github.com/ClickHouse/arrow/pull/16). [#47958](https://github.com/ClickHouse/ClickHouse/pull/47958) ([Arthur Passos](https://github.com/arthurpassos)).
- Restore the ability of native macOS debug server build to start. [#48050](https://github.com/ClickHouse/ClickHouse/pull/48050) ([Robert Schulze](https://github.com/rschu1ze)). Note: this change is only relevant for development, as the ClickHouse official builds are done with cross-compilation.

#### Bug Fix (user-visible misbehavior in an official stable release)[​](#bug-fix-user-visible-misbehavior-in-an-official-stable-release-9 "Direct link to Bug Fix (user-visible misbehavior in an official stable release)")
2023 Changelog

- A few query rewrite optimizations: `sumIf(123, cond) -> 123 * countIf(1, cond)`, `sum(if(cond, 123, 0)) -> 123 * countIf(cond)`, `sum(if(cond, 0, 123)) -> 123 * countIf(not(cond))` [#44728](https://github.com/ClickHouse/ClickHouse/pull/44728) ([李扬](https://github.com/taiyang-li)).
- Improved how memory bound merging and aggregation in order on top query plan interact. Previously we fell back to explicit sorting for AIO in some cases when it wasn't actually needed. [#45892](https://github.com/ClickHouse/ClickHouse/pull/45892) ([Nikita Taranov](https://github.com/nickitat)).
- Concurrent merges are scheduled using round-robin by default to ensure fair and starvation-free operation. Previously in heavily overloaded shards, big merges could possibly be starved by smaller merges due to the use of strict priority scheduling. Added `background_merges_mutations_scheduling_policy` server config option to select scheduling algorithm (`round_robin` or `shortest_task_first`). [#46247](https://github.com/ClickHouse/ClickHouse/pull/46247) ([Sergei Trifonov](https://github.com/serxa)).