clintropolis commented on code in PR #15173: URL: https://github.com/apache/druid/pull/15173#discussion_r1378261970
########## docs/do-not-merge.md: ########## @@ -0,0 +1,815 @@ +<!--Intentionally, there's no Apache license so that the GHA fails it. This file is not meant to be merged. +--> + +Apache Druid 28.0.0 contains over $NUMBER_FEATURES new features, bug fixes, performance enhancements, documentation improvements, and additional test coverage from $NUMBER_OF_CONTRIBUTORS contributors. + +See the [complete set of changes](https://github.com/apache/druid/issues?q=is%3Aclosed+milestone%3A28.0+sort%3Aupdated-desc+) for additional details, including bug fixes. + +Review the [upgrade notes](#upgrade-notes) and [incompatible changes](#incompatible-changes) before you upgrade to Druid 28.0.0. + +# Important changes and deprecations + +In Druid 28.0.0, we have made substantial improvements to querying to make the system more ANSI SQL compatible. This includes changes in handling NULL and boolean values as well as boolean logic. At the same time, the Apache Calcite library has been upgraded to the latest version. While we have documented known query behavior changes, please read the [upgrade notes](#upgrade-notes) section carefully. Test your application before rolling out to broad production scenarios while closely monitoring the query status. + +## SQL compatibility + +Druid continues to make SQL query execution more consistent with how standard SQL behaves. However, there are feature flags available to restore the old behavior if needed. + +### Three-valued logic + +Druid native filters now observe SQL [three-valued logic](https://en.wikipedia.org/wiki/Three-valued_logic#SQL) (`true`, `false`, or `unknown`) instead of Druid's classic two-state logic when you set the following configuration values: + +* `druid.generic.useThreeValueLogicForNativeFilters = true` +* `druid.expressions.useStrictBooleans = true` +* `druid.generic.useDefaultValueForNull = false` + +[#15058](https://github.com/apache/druid/pull/15058) + +### Strict booleans + +`druid.expressions.useStrictBooleans` is now enabled by default. +Druid now handles booleans strictly using `1` (true) or `0` (false). +Previously, true and false could be represented either as `true` and `false` as well as `1` and `0`, respectively. +In addition, Druid now returns a null value for Boolean comparisons like `True && NULL`. + +If you don't explicitly configure this property in `runtime.properties`, clusters now use LONG types for any ingested boolean values and in the output of boolean functions for transformations and query time operations. + +This change may impact your query results. For more information, see [SQL compatibility in the upgrade notes](#sql-compatibility-1). + +[#14734](https://github.com/apache/druid/pull/14734) + +### NULL handling + +`druid.generic.useDefaultValueForNull` is now disabled by default. +Druid now differentiates between empty records and null records. +Previously, Druid might treat empty records as empty or null. + +This change may impact your query results. For more information, see [SQL compatibility in the upgrade notes](#sql-compatibility-1). + +[#14792](https://github.com/apache/druid/pull/14792) + +## SQL planner improvements + +Druid uses Apache Calcite for SQL planning and optimization. Starting in Druid 28.0.0, the Calcite version has been upgraded from 1.21 to 1.35. This upgrade brings in many bug fixes in SQL planning from Calcite. As part of the upgrade, the behavior of type inference for [dynamic parameters](#dynamic-parameters) and the [recommended syntax for UNNEST](#new-syntax-for-sql-unnest) have changed. + +### Dynamic parameters + +The behavior of type inference for dynamic parameters has changed. To avoid any type interference issues, explicitly `CAST` all dynamic parameters as a specific data type in SQL queries. For example, use: + +```sql +SELECT (1 * CAST (? as DOUBLE))/2 as tmp +``` + +Do not use: + +```sql +SELECT (1 * ?)/2 as tmp +``` + +### New syntax for SQL UNNEST + +The recommended syntax for SQL UNNEST has changed. We recommend using CROSS JOIN instead of commas for most queries to prevent issues with precedence. For example, use: + +```sql +SELECT column_alias_name1 FROM datasource CROSS JOIN UNNEST(source_expression1) AS table_alias_name1(column_alias_name1) CROSS JOIN UNNEST(source_expression2) AS table_alias_name2(column_alias_name2), ... +``` + +Do not use: + +```sql +SELECT column_alias_name FROM datasource, UNNEST(source_expression1) AS table_alias_name1(column_alias_name1), UNNEST(source_expression2) AS table_alias_name2(column_alias_name2), ... +``` + +## Async query and query from deep storage + +[Query from deep storage](https://druid.apache.org/docs/latest/querying/query-deep-storage/) is no longer an experimental feature. When you query from deep storage, more data is available for queries without having to scale your Historical services to accommodate more data. To benefit from the space saving that query from deep storage offers, configure your load rules to unload data from your Historical services. + +## MSQ queries for realtime tasks + +The MSQ task engine can now include real time segments in query results. To do this, use the `includeSegmentSource` context parameter and set it to `REALTIME`. + +[#15024](https://github.com/apache/druid/pull/15024) + +## MSQ support for UNION ALL queries + +You can now use the MSQ task engine to run UNION ALL queries with `UnionDataSource`. + +[#14981](https://github.com/apache/druid/pull/14981) + +## Ingest from multiple Kafka topics to a single datasource + +You can now ingest streaming data from multiple Kafka topics to a datasource using a single supervisor. +You configure the topics for the supervisor spec using a regex pattern as the value for `topicPattern` in the IO config. If you add new topics to Kafka that match the regex, Druid automatically starts ingesting from those new topics. + +If you enable multi-topic ingestion for a datasource, downgrading will cause the Supervisor to fail. +For more information, see [Stop supervisors that ingest from multiple Kafka topics before downgrading](#stop-supervisors-that-ingest-from-multiple-kafka-topics-before-downgrading). + +[#14424](https://github.com/apache/druid/pull/14424) +[#14865](https://github.com/apache/druid/pull/14865) + +## SQL UNNEST and ingestion flattening + +The UNNEST function is no longer experimental. UNNEST lets you flatten and explode data during batch ingestion. For more information, see [UNNEST](https://druid.apache.org/docs/latest/querying/sql/#unnest) and [Unnest arrays within a column](https://druid.apache.org/docs/latest/tutorials/tutorial-unnest-arrays/). + +You no longer need to include the context parameter `enableUnnest: true` to use UNNEST. + +[#14886](https://github.com/apache/druid/pull/14886) + +## Window functions (experimental) + +You can use [window functions](https://druid.apache.org/docs/latest/querying/sql-window-functions) in Apache Druid to produce values based upon the relationship of one row within a window of rows to the other rows within the same window. A window is a group of related rows within a result set. For example, rows with the same value for a specific dimension. + +Enable window functions in your query with the `enableWindowing: true` context parameter. + +[#15184](https://github.com/apache/druid/pull/15184) + +## Concurrent append and replace (experimental) + +Druid 28.0.0 adds experimental support for concurrent append and replace. +This feature allows you to safely replace the existing data in an interval of a datasource while new data is being appended to that interval. One of the most common applications of this is appending new data to an interval while compaction of that interval is already in progress. +For more information, see [Concurrent append and replace](https://druid.apache.org/docs/latest/data-management/automatic-compaction#concurrent-append-and-replace). + +Segment locking will be deprecated and removed in favor of concurrent append and replace that is much simpler in design. With concurrent append and replace, Druid doesn't lock compaction jobs out because of active realtime ingestion. + +# Functional area and related changes + +## Web console + +### Added UI support for segment loading query context parameter + +The web console supports the `waitUntilSegmentsLoad` query context parameter. + + + +[#15110](https://github.com/apache/druid/pull/15110) + +### Added concurrent append and replace switches + +The web console includes concurrent append and replace switches. + +The following screenshot shows the concurrent append and replace switches in the classic batch ingestion wizard: + + +The following screenshot shows the concurrent append and replace switches in the compaction configuration UI: + + +[#15114](https://github.com/apache/druid/pull/15114) + +### Added UI support for ingesting from multiple Kafka topics to a single datasource + +The web console supports ingesting streaming data from multiple Kafka topics to a datasource using a single supervisor. + + + +[#14833](https://github.com/apache/druid/pull/14833) + +### Other web console improvements + +* You can now copy query results from the web console directly to the clipboard [#14889](https://github.com/apache/druid/pull/14889) +* The web console now shows the execution dialog for `query_controller` tasks in the task view instead of the generic raw task details dialog. You can still access the raw task details from the ellipsis (...) menu [#14930)](https://github.com/apache/druid/pull/14930) +* You can now select a horizontal range in the web console time chart to modify the current WHERE clause [#14929](https://github.com/apache/druid/pull/14929) +* You can now set dynamic query parameters in the web console [#14921](https://github.com/apache/druid/pull/14921) +* You can now edit the Coordinator dynamic coonfiguration in the web console [#14791](https://github.com/apache/druid/pull/14791) +* You can now prettify SQL queries and use flatten with a Kafka input format [#14906](https://github.com/apache/druid/pull/14906) +* A warning now appears when a CSV or TSV sample contains newlines that Druid does not accept [#14783](https://github.com/apache/druid/pull/14783) +* You can now select a format when downloading data [#14794](https://github.com/apache/druid/pull/14794) +* Improved the clarity of cluster default rules in the retention dialog [#14793](https://github.com/apache/druid/pull/14793) +* The web console now detects inline queries in the query text and lets you run them individually [#14810](https://github.com/apache/druid/pull/14801) +* You can now reset specific partition offsets for a supervisor [#14863](https://github.com/apache/druid/pull/14863) + +## Multi-stage query + +### Support for multiple result formats + +Query from deep storage now supports multiple result formats. +Previously, the `/druid/v2/sql/statements/` endpoint only supported results in the `object` format. Now, results can be written in any format specified in the `resultFormat` parameter. +For more information on result parameters supported by the Druid SQL API, see [Responses](https://druid.apache.org/docs/latest/api-reference/sql-api#responses). + +[#14571](https://github.com/apache/druid/pull/14571) + +### Broadened access for queries from deep storage + +Users with the `STATE` permission can interact with status APIs for queries from deep storage. Previously, only the user who submitted the query could use those APIs. This enables the web console to monitor the running status of the queries. Users with the `STATE` permission can access the query results. Review Comment: i personally think we should combine stuff as much as possible - i kind of felt like i was re-reading stuff i had already read in a few places, which is why i brought this up -- This is an automated message from the Apache Git Service. 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