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Altinity Stable for ClickHouse 21.8
- 1: Altinity Stable for ClickHouse 21.8.15
- 2: Altinity Stable for ClickHouse 21.8.13
- 3: Altinity Stable for ClickHouse 21.8.12
- 4: Altinity Stable for ClickHouse 21.8.11
- 5: Altinity Stable for ClickHouse 21.8.10
- 6: Altinity Stable for ClickHouse 21.8.8
1 - Altinity Stable for ClickHouse 21.8.15
Based on upstream/v184.108.40.206-lts.
ClickHouse release v220.127.116.11-altinitystable as compared to community ClickHouse v18.104.22.168:
Changes compared to the Community Build
- Bug Fix: Fixed issue with merging configs that have and root XML tags. (backport of ClickHouse@213ecae) (via #114).
- Bug Fix: Backport of ClickHouse#31823 to 21.8: Fix invalid cast of nullable type when nullable primary key is used (via #110)
- Build/Testing/Packaging Improvement: Various macOS compilation and packaging fixes/backporting (via #108)
- Build/Testing/Packaging Improvement: Minor test improvements (via afb4a0a, 4c35386)
Changes compared to Altinity Stable 22.214.171.124
- Fix segfault while parsing ORC file with corrupted footer. Closes ClickHouse#33797 via ClickHouse#33984 Kruglov Pavel.
- Fix usage of functions array and tuple with literal arguments in distributed queries. Previously it could lead to Not found columns exception. ClickHouse#33938 (Anton Popov).
- Fix s3 table function reading empty file. Closes ClickHouse#33008 via ClickHouse#33037 (Kseniia Sumarokova).
- Fix hdfs url check that didn’t allow using HA namenode address. Bug was introduced in ClickHouse#31042. ClickHouse#32976 (Kruglov Pavel).
- Server might fail to start if database with MySQL engine cannot connect to MySQL server, it’s fixed. Fixes ClickHouse#14441 via ClickHouse#32802 (tavplubix).
2 - Altinity Stable for ClickHouse 21.8.13
ClickHouse release v126.96.36.199-altinitystable as compared to v188.8.131.52-altinitystable:
Some replication queue entries might hang for
temporary_directories_lifetime(1 day by default) with
Part ... (state Deleting) already exists, but it will be deleted soonor similar error. It’s fixed. Fixes #29616. #32201 (tavplubix).
GET_PARTentry might hang in replication queue if part is lost on all replicas and there are no other parts in the same partition. It’s fixed in cases when partition key contains only columns of integer types or
Date[Time]. Fixes #31485. #31887 (tavplubix).
Change configuration path from
keeper_server.coordination_settings.session_timeout_mswhen constructing a
KeeperTCPHandler- Same with
operation_timeout. #31859 (JackyWoo).
Changes compared to the Community Build
- Fix invalid cast of Nullable type when nullable primary key is used. (Nullable primary key is a discouraged feature - please do not use). This fixes #31075 #31823 Amos Bird).
3 - Altinity Stable for ClickHouse 21.8.12
ClickHouse release v184.108.40.206-altinitystable as compared to v220.127.116.11-altinitystable:
Bug Fixes (user-visible misbehaviour in official stable or prestable release)
- Fixed functions
notEmptywith the arguments of
UUIDtype. Fixes #31819. #31883 (Anton Popov).
- Fixed possible assertion
../src/IO/ReadBuffer.h:58: bool DB::ReadBuffer::next(): Assertion '!hasPendingData()' failed.in TSKV format. #31804 (Kruglov Pavel).
- Fixed usage of
Buffertable engine with type
Map. Fixes #30546. #31742 (Anton Popov).
- Fixed race in JSONEachRowWithProgress output format when data and lines with progress are mixed in output. #31736 (Kruglov Pavel).
there are no such cluster hereerror on execution of
ON CLUSTERquery if specified cluster name is name of
Replicateddatabase. #31723 (tavplubix).
input_format_allow_errors_ratiodid not work for parsing of domain types, such as
IPv4, it’s fixed. Fixes #31686. #31697 (tavplubix).
RENAME TABLEquery worked incorrectly on attempt to rename an DDL dictionary in
Ordinarydatabase, it’s fixed. #31638 (tavplubix).
- Fix invalid generated JSON when only column names contain invalid UTF-8 sequences. #31534 (Kevin Michel).
nullptrin STS credentials provider for S3. #31409 (Vladimir Chebotarev).
- Remove not like function into RPNElement. #31169 (sundyli).
- Fixed bug in Keeper which can lead to inability to start when some coordination logs was lost and we have more fresh snapshot than our latest log. #31150 (alesapin).
- Fixed abort in debug server and
DB::Exception: std::out_of_range: basic_stringerror in release server in case of bad hdfs url by adding additional check of hdfs url structure. #31042 (Kruglov Pavel).
4 - Altinity Stable for ClickHouse 21.8.11
ClickHouse release v18.104.22.168-altinitystable FIXME as compared to v22.214.171.124-altinitystable
CompiledExpressionCachelimit elements size using
compiled_expression_cache_elements_sizesetting. #30667 (Maksim Kita).
- Made query which fetched table structure for PostgreSQL database more reliable. #30477 (Kseniia Sumarokova).
Bug Fixes (user-visible misbehaviour in official stable or prestable release)
StorageMergewith aliases and where (it did not work before at all). Closes #28802. #31044 (Kseniia Sumarokova).
Querywith quoted identifiers. This allows to have spaces in json path. Closes #30971. #31003 (Kseniia Sumarokova).
formatRowfunction with not row formats led to segfault. Don’t allow to use this function with such formats (because it doesn’t make sense). #31001 (Kruglov Pavel).
max_partition_size_to_dropcheck in case of
ATTACH PARTITION ... FROMand
MOVE PARTITION ...#30995 (Amr Alaa).
- Fixed set index not used in
AND/ORexpressions when there are more than two operands. This fixes #30416 . #30887 (Amos Bird).
- Fixed ambiguity when extracting auxiliary ZooKeeper name from ZooKeeper path in
ReplicatedMergeTree. Previously server might fail to start with
Unknown auxiliary ZooKeeper nameif ZooKeeper path contains a colon. Fixes #29052. Also it was allowed to specify ZooKeeper path that does not start with slash, but now it’s deprecated and creation of new tables with such path is not allowed. Slashes and colons in auxiliary ZooKeeper names are not allowed too. #30822 (tavplubix).
- Fixed a race condition between
REPLACE/MOVE PARTITIONand background merge in non-replicated
MergeTreethat might cause a part of moved/replaced data to remain in partition. Fixes #29327. #30717 (tavplubix).
WHEREin case of always true
PREWHERE. #30668 (Azat Khuzhin).
- Functions for case-insensitive search in UTF8 strings like
countSubstringsCaseInsensitiveUTF8might find substrings that actually does not match is fixed. #30663 (tavplubix).
- Limit push down optimization could cause a error
Cannot find column. Fixes #30438. #30562 (Nikolai Kochetov).
- Fixed exception handling in
parallel_view_processing. This resolves issues / prevents crashes in some rare corner cases when that feature is enabled and exception (like
Memory limit exceeded ...) happened in the middle of materialized view processing. #30472 (filimonov).
- Fixed segfault which might happen if session expired during execution of
REPLACE PARTITION. #30432 (tavplubix).
preallocateoption from layout config. #30246 (Maksim Kita).
[I]LIKEfunction. Closes #28661. #30244 (Nikolay Degterinsky).
- Support nullable arguments in function
initializeAggregation. #30177 (Anton Popov).
- Fixed data-race between
StorageLog. #29946 (Azat Khuzhin).
- Fixed hanging DDL queries on Replicated database while adding a new replica. #29328 (Kevin Michel).
- Fixed bad optimizations of
ORDER BYif it contains
WITH FILL. This closes #28908. This closes #26049. #28910 (alexey-milovidov).
- Fixed queries to external databases (i.e. MySQL) with multiple columns in
(k,v) IN ((1, 2))) (but note that this has some backward incompatibility for the
clickhouse-copiersince it uses alias for tuple element). #28888 (Azat Khuzhin).
- Fixed “Column is not under aggregate function and not in GROUP BY” with
PREWHERE(Fixes: #28461). #28502 (Azat Khuzhin).
NOT-INindex optimization when not all key columns are used. This fixes #28120. #28315 (Amos Bird).
Bug Fixes (user-visible misbehaviour in official stable or prestable release
5 - Altinity Stable for ClickHouse 21.8.10
Release notes for Altinity Stable 21.8.10
ClickHouse release 21.8.10 as compared to v21.8.8
- Update zoneinfo files to 2021c. #29925 (alexey-milovidov).
- Allow symlinks to files in user_files directory for file table function. #30309 (Kseniia Sumarokova).
- Fix shutdown of
AccessControlManager. Now there can’t be reloading of the configuration after AccessControlManager has been destroyed. This PR fixes the flaky test test_user_directories/test.py::test_relative_path. #29951 (Vitaly Baranov).
- Allow using a materialized column as the sharding key in a distributed table even if
insert_allow_materialized_columns=0:. #28637 (Vitaly Baranov).
- FlatDictionary, HashedDictionary fix bytes_allocated calculation for nullable attributes. #30238 (Maksim Kita).
Memorydatabase might reappear after server restart, it’s fixed (#29795). Also added
force_remove_data_recursively_on_dropsetting as a workaround for
Directory not emptyerror when dropping
Ordinarydatabase (because it’s not possible to remove data leftovers manually in cloud environment). #30054 (tavplubix).
- Fix crash of sample by
tuple(), closes #30004. #30016 (Flynn).
- Fix possible data-race between
StorageStripeLog. #29959 (Azat Khuzhin).
- Fix system tables recreation check (fails to detect changes in enum values). #29857 (Azat Khuzhin).
Timeout exceeded: elapsed 18446744073.709553 secondserror that might happen in extremely rare cases, presumably due to some bug in kernel. Fixes #29154. #29811 (tavplubix).
- Fix bad cast in
ATTACH TABLE ... FROM 'path'query when non-string literal is used instead of path. It may lead to reading of uninitialized memory. #29790 (alexey-milovidov).
- Fix concurrent access to
GROUP BY(leads to SIGSEGV). #29782 (Azat Khuzhin).
- Fixed incorrect behaviour of setting
materialized_postgresql_tables_listat server restart. Found in #28529. #29686 (Kseniia Sumarokova).
- Condition in filter predicate could be lost after push-down optimisation. #29625 (Nikolai Kochetov).
- Fix rare segfault in
ALTER MODIFYquery when using incorrect table identifier in
x.y.z...Fixes #29184. #29573 (alesapin).
- Fix bug in check
pathStartsWithbecuase there was bug with the usage of
The behavior is undefined if the second range is shorter than the first range.. #29531 (Kseniia Sumarokova).
- In ODBC bridge add retries for error Invalid cursor state. It is a retriable error. Closes #29473. #29518 (Kseniia Sumarokova).
- Fix possible
Block structure mismatchfor subqueries with pushed-down
HAVINGpredicate. Fixes #29010. #29475 (Nikolai Kochetov).
- Avoid deadlocks when reading and writting on JOIN Engine tables at the same time. #30187 (Raúl Marín).
- Fix INSERT SELECT incorrectly fills MATERIALIZED column based of Nullable column. #30189 (Azat Khuzhin).
- Fix null deference for
GROUP BY WITH TOTALS HAVING(when the column from
HAVINGwasn’t selected). #29553 (Azat Khuzhin).
6 - Altinity Stable for ClickHouse 21.8.8
A few months ago we certified ClickHouse 21.3 as an Altinity Stable release. Since then, we have worked on newer releases and run them in-house. We completed several new features, and even more have been added by community contributors. We were running ClickHouse 21.8 to power our public datasets at Altinity.Cloud instance and testing it in our environments. We have also performed a comprehensive QA of ClickHouse 21.8 to make sure upgrades go smoothly. As of 21.8.8 we are confident in certifying 21.8 as an Altinity Stable release.
This release is a significant upgrade since the previous Altinity Stable release. It includes 1472 pull requests from 224 contributors. Please look below for the detailed release notes.
Major new features since the previous stable release 21.3
A new release introduces a lot of changes and new functions. The full list is available in the Appendix, so refer to this section for more detail. The following new features are worth mentioning on the front page:
- SQL features:
DISTINCT ONa subset of columns
- Partial support of SQL/JSON standard
- Arrays in dictionaries are now supported
- Arrays and nested data types are now supported for Parquet and Arrow formats
- DateTime64 extended range, Now dates between 1925 to 2283 years are supported. a)
- Security features:
- Disk level encryption
- Kerberos authentication for HTTP protocol a)
- Active Directory groups mapping for LDAP user directory a)
- Replication and Cluster improvements:
- ClickHouse Keeper (experimental) – in-process ZooKeeper replacement
- SYSTEM RESTORE REPLICA – a handy tool that makes life easier in the unfortunate occasion if ZooKeeper metadata is lost a)
- Support for MySQL/PostgreSQL clusters when using mysql/postgresql table functions
- Zero-copy replication for S3 tables (see Altinity blog post for details)
- Parts movement between shards (experimental)
- MergeTree features:
MaterializedPostgreSQLdatabase engine for replication from PostgreSQL
- HDFS disk support (experimental)
- Allow to catch Kafka errors into a separate stream (see the KB article on this)
- YAML configuration format as an alternative to XML
As usual with ClickHouse, there are many performance and operational improvements in different server components.
a) - contributed by Altinity developers.
Backward Incompatible Changes
The following changes are backward incompatible and require user attention during an upgrade:
- Users of
LowCardinality(Nullable(...))can not safely downgrade to versions older than 21.4. Data in tables with columns of those types inserted / merged by 21.8 will be lost after the downgrade.
- Values of
UUIDtype cannot be compared with integers. For example, instead of writing
uuid != 0type
uuid != '00000000-0000-0000-0000-000000000000'
toStartOfIntervalFunctionwill align hour intervals to midnight (in previous versions they were aligned to the start of unix epoch). For example,
toStartOfInterval(x, INTERVAL 11 HOUR)will split every day into three intervals:
- It’s not possible to rollback to the older ClickHouse version after executing
ALTER ... ATTACHquery as the old servers would fail to process the new command entry
ATTACH_PARTin the replicated log.
- The behaviour of
remote_url_allow_hostshas changed. In previous versions the empty section did nothing, in 21.8 it will block access to all external hosts. Remove this section from the configuration files after an upgrade if you experience issues with url() or s3() functions.
- If you will downgrade to version before 21.1 clickhouse will not be able to start automatically – you will need to remove the system.*_log tables manually to downgrade
- There is an issue with uniqueState(UUID) in AggregatingMergeTree tables, and can be corrected by replacing
in MATERIALIZED VIEWs
with uniqState(sipHash64(uuid))and change data type for already saved data from
AggregateFunction(uniq, UInt64). For more information see the following:
There were several changes between versions that may affect the rolling upgrade of big clusters. Upgrading only part of the cluster is not recommended.
- Distributed queries with explicitly defined large sets are now executed differently. Compatibility setting
legacy_column_name_of_tuple_literalmay be enabled during the rolling upgrade of the cluster. Otherwise distributed queries with explicitly defined sets at IN clause may fail during upgrade.
ATTACH PART[ITION]queries may not work during cluster upgrade
Other Important Changes
ClickHouse embedded monitoring has become a bit more aggressive. It now collects several system stats, and stores them in the table
system.asynchronious_metric_log. This can be visible as an increase of background writes, storage usage, etc. To return to the old rate of metrics refresh / flush, adjust those settings in
<asynchronous_metrics_update_period_s> 60 </asynchronous_metrics_update_period_s> <asynchronous_metric_log> <flush_interval_milliseconds> 60000 </flush_interval_milliseconds> </asynchronous_metric_log>
Alternatively, metric_log and asynchronous_metric_log tables can be completely disabled:
<yandex> <asynchronous_metric_log remove="1"/> <metric_log remove="1"/> </yandex>
Some new ClickHouse features are now enabled by default. It may lead to a change in behaviour, so review those carefully and disable features that may affect your system:
In the previous releases we recommended disabling
optimize_on_insert. This recommendation stays for 21.8 as well as inserts into
AggregatingMergeTree can slow down.
Known issues in 21.8.8
The development team continues to improve the quality of the 21.8 release. The following issues still exist in the 21.8.8 version and may affect ClickHouse operation. Please inspect them carefully to decide if those are applicable to your applications:
system.events for event = 'Merge'are overstated. ClickHouse incorrectly increments this counter.
Timeout exceeded: elapsed 18446744073.709553 secondserror that might happen in extremely rare cases, presumably due to some bug in kernel.
You may also look into a GitHub issues using a special v21.8-affected label.
ClickHouse Altinity Stable Releases are based on the community versions. For more information on installing ClickHouse from either the Altinity Stable builds or the community builds, see the ClickHouse Altinity Stable Release Build Install Guide.
Please contact us at email@example.com if you experience any issues with the upgrade.
- DateTime functions:
timeZone, timeZoneOf, timeZoneOffset, timezoneOf, toTimezone
- JSON processing functions:
JSON_EXISTS, JSON_QUERY, JSON_VALUE
simpleJSONExtractBool, simpleJSONExtractFloat, simpleJSONExtractInt, simpleJSONExtractRaw, simpleJSONExtractString, simpleJSONExtractUInt, simpleJSONHas
- String functions:
leftPad, lpad, leftPadUTF8
rightPad, rpad, rightPadUTF8
- Array functions:
- Aggregate functions
readWktMultiPolygon, readWktPoint, readWktPolygon, readWktRing
- Type related:
toUInt128, toUInt128OrNull, toUInt128OrZero
partitionId– that corresponds to
_partition_id virtualcolumn added to MergeTree tables
New table functions
s3Cluster– see our blog article that highlights this one
New table engines
ExternalDistributed– allows to query MySQL or PostgreSQL clusters
New metrics and events
The table has also got a lot of new metrics for a host monitoring rather than ClickHouse.
New system tables
- database, table, name, type, expr, granularity
- database, table, task_name, task_uuid, create_time, part_name, part_uuid, to_shard, update_time, state, num_tries, last_exception
projection_parts– same as parts but with extra ‘parent_*’ columns
projection_parts_columns– same as parts_columns but with extra ‘parent_*’ columns
New columns in system tables
key.names, key.types, found_rate
last_error_time, last_error_message, last_error_trace, remote
- multiple columns
uuid, min_time, max_time
- Settings (Map replaces Settings.Names/Values arrays), ProfileEvents (Map replaces ProfileEvents.Names/Values arrays), current_database
projections, initial_query_start_time, initial_query_start_time_microseconds, Settings (Map replaces Settings.Names/Values arrays), ProfileEvents (Map replaces ProfileEvents.Names/Values arrays)
initial_query_start_time_microseconds, Settings (Map replaces Settings.Names/Values arrays), ProfileEvents (Map replaces ProfileEvents.Names/Values arrays)
grantees_any, grantees_list, grantees_except
|Name||Old value||New value||Description|
|max_parts_to_merge_at_once||100||Max amount of parts which can be merged at once (0 - disabled). Doesn’t affect OPTIMIZE FINAL query.|
|max_replicated_fetches_network_bandwidth||0||The maximum speed of data exchange over the network in bytes per second for replicated fetches. Zero means unlimited.|
|max_replicated_sends_network_bandwidth||0||The maximum speed of data exchange over the network in bytes per second for replicated sends. Zero means unlimited.|
|min_bytes_to_rebalance_partition_over_jbod||0||Minimal amount of bytes to enable part rebalance over JBOD array (0 - disabled).|
|non_replicated_deduplication_window||0||How many last blocks of hashes should be kept on disk (0 - disabled).|
|part_moves_between_shards_delay_seconds||30||Time to wait before/after moving parts between shards.|
|part_moves_between_shards_enable||0||Experimental/Incomplete feature to move parts between shards. Does not take into account sharding expressions.|
|replicated_fetches_http_connection_timeout||0||HTTP connection timeout for part fetch requests. Inherited from default profile http_connection_timeout if not set explicitly.|
|replicated_fetches_http_receive_timeout||0||HTTP receive timeout for fetch part requests. Inherited from default profile http_receive_timeout if not set explicitly.|
|replicated_fetches_http_send_timeout||0||HTTP send timeout for part fetch requests. Inherited from default profile http_send_timeout if not set explicitly.|
|remote_fs_execute_merges_on_single_replica_time_threshold||10800||When greater than zero only a single replica starts the merge immediately when merged part on shared storage and ‘allow_remote_fs_zero_copy_replication’ is enabled.|
|Type||Name||Old value||New value||Description|
|settings||allow_experimental_bigint_types||0||1||Obsolete setting, does nothing.|
|settings||allow_experimental_codecs||0||If it is set to true, allow to specify experimental compression codecs (but we don't have those yet and this option does nothing).|
|settings||allow_experimental_database_materialized_postgresql||0||Allow to create database with Engine=MaterializedPostgreSQL(…).|
|settings||allow_experimental_funnel_functions||0||Enable experimental functions for funnel analysis.|
|settings||allow_experimental_map_type||0||1||Obsolete setting, does nothing.|
|settings||allow_experimental_projection_optimization||0||Enable projection optimization when processing SELECT queries|
|settings||async_socket_for_remote||0||1||Asynchronously read from socket executing remote query|
|settings||background_schedule_pool_size||16||128||Number of threads performing background tasks for replicated tables, dns cache updates. Only has meaning at server startup.|
|settings||compile_aggregate_expressions||1||Compile aggregate functions to native code.|
|settings||compile_expressions||0||1||Compile some scalar functions and operators to native code.|
|settings||cross_to_inner_join_rewrite||1||Use inner join instead of comma/cross join if possible|
|settings||database_replicated_always_detach_permanently||0||Execute DETACH TABLE as DETACH TABLE PERMANENTLY if database engine is Replicated|
|settings||distributed_ddl_entry_format_version||1||Version of DDL entry to write into ZooKeeper|
|settings||distributed_ddl_output_mode||throw||Format of distributed DDL query result|
|settings||distributed_directory_monitor_split_batch_on_failure||0||Should StorageDistributed DirectoryMonitors try to split batch into smaller in case of failures.|
|settings||distributed_push_down_limit||0||If 1, LIMIT will be applied on each shard separatelly. Usually you don't need to use it, since this will be done automatically if it is possible, i.e. for simple query SELECT FROM LIMIT.|
|settings||experimental_query_deduplication_send_all_part_uuids||0||If false only part UUIDs for currently moving parts are sent. If true all read part UUIDs are sent (useful only for testing).|
|settings||external_storage_max_read_bytes||0||Limit maximum number of bytes when table with external engine should flush history data. Now supported only for MySQL table engine, database engine, dictionary and MaterializeMySQL. If equal to 0, this setting is disabled|
|settings||external_storage_max_read_rows||0||Limit maximum number of rows when table with external engine should flush history data. Now supported only for MySQL table engine, database engine, dictionary and MaterializeMySQL. If equal to 0, this setting is disabled|
|settings||force_optimize_projection||0||If projection optimization is enabled, SELECT queries need to use projection|
|settings||glob_expansion_max_elements||1000||Maximum number of allowed addresses (For external storages, table functions, etc).|
|settings||group_by_two_level_threshold_bytes||100000000||50000000||From what size of the aggregation state in bytes, a two-level aggregation begins to be used. 0 - the threshold is not set. Two-level aggregation is used when at least one of the thresholds is triggered.|
|settings||handle_kafka_error_mode||default||Obsolete setting, does nothing.|
|settings||http_max_field_name_size||1048576||Maximum length of field name in HTTP header|
|settings||http_max_field_value_size||1048576||Maximum length of field value in HTTP header|
|settings||http_max_fields||1000000||Maximum number of fields in HTTP header|
|settings||http_max_uri_size||1048576||Maximum URI length of HTTP request|
|settings||insert_null_as_default||1||Insert DEFAULT values instead of NULL in INSERT SELECT (UNION ALL)|
|settings||legacy_column_name_of_tuple_literal||0||List all names of element of large tuple literals in their column names instead of hash. This settings exists only for compatibility reasons. It makes sense to set to 'true', while doing rolling update of cluster from version lower than 21.7 to higher.|
|settings||max_distributed_depth||5||Maximum distributed query depth|
|settings||max_replicated_fetches_network_bandwidth_for_server||0||The maximum speed of data exchange over the network in bytes per second for replicated fetches. Zero means unlimited. Only has meaning at server startup.|
|settings||max_replicated_sends_network_bandwidth_for_server||0||The maximum speed of data exchange over the network in bytes per second for replicated sends. Zero means unlimited. Only has meaning at server startup.|
|settings||min_count_to_compile_aggregate_expression||3||The number of identical aggregate expressions before they are JIT-compiled|
|settings||normalize_function_names||1||0||Normalize function names to their canonical names|
|settings||odbc_bridge_connection_pool_size||16||Connection pool size for each connection settings string in ODBC bridge.|
|settings||optimize_functions_to_subcolumns||0||Transform functions to subcolumns, if possible, to reduce amount of read data. E.g. 'length(arr)' -> 'arr.size0', 'col IS NULL' -> 'col.null'|
|settings||optimize_fuse_sum_count_avg||0||Fuse aggregate functions sum(), avg(), count() with identical arguments into one sumCount() call, if the query has at least two different functions|
|settings||optimize_move_to_prewhere_if_final||0||If query has
|settings||optimize_skip_unused_shards_limit||1000||Limit for number of sharding key values, turns off optimize_skip_unused_shards if the limit is reached|
|settings||optimize_skip_unused_shards_rewrite_in||1||Rewrite IN in query for remote shards to exclude values that does not belong to the shard (requires optimize_skip_unused_shards)|
|settings||output_format_arrow_low_cardinality_as_dictionary||0||Enable output LowCardinality type as Dictionary Arrow type|
|settings||postgresql_connection_pool_size||16||Connection pool size for PostgreSQL table engine and database engine.|
|settings||postgresql_connection_pool_wait_timeout||5000||Connection pool push/pop timeout on empty pool for PostgreSQL table engine and database engine. By default it will block on empty pool.|
|settings||prefer_column_name_to_alias||0||Prefer using column names instead of aliases if possible.|
|settings||prefer_global_in_and_join||0||If enabled, all IN/JOIN operators will be rewritten as GLOBAL IN/JOIN. It's useful when the to-be-joined tables are only available on the initiator and we need to always scatter their data on-the-fly during distributed processing with the GLOBAL keyword. It's also useful to reduce the need to access the external sources joining external tables.|
|settings||query_plan_enable_optimizations||1||Apply optimizations to query plan|
|settings||query_plan_filter_push_down||1||Allow to push down filter by predicate query plan step|
|settings||s3_max_single_read_retries||4||The maximum number of retries during single S3 read.|
|settings||sleep_in_send_data_ms||0||Time to sleep in sending data in TCPHandler|
|settings||sleep_in_send_tables_status_ms||0||Time to sleep in sending tables status response in TCPHandler|
Also, please refer to the release notes from the development team available at the following URLs:
- 21.4 release notes: https://clickhouse.com/docs/en/whats-new/changelog/#clickhouse-release-21-4
- 21.5 release notes: https://clickhouse.com/docs/en/whats-new/changelog/#clickhouse-release-21-5-2021-05-20
- 21.6 release notes: https://clickhouse.com/docs/en/whats-new/changelog/#clickhouse-release-21-6-2021-06-05
- 21.7 release notes: https://clickhouse.com/docs/en/whats-new/changelog/#clickhouse-release-v21-7-2021-07-09
- 21.8 release notes: https://clickhouse.com/docs/en/whats-new/changelog/#clickhouse-release-v21-8-2021-08-12